TIP TIG welding is 100 to 500% faster than TIG with superior quality than traditional TIG - Pulsed MIG - FCAW

TIP TIG Welding

 

TIG Welding Aluminum - Tips.

Tig Welding Aluminum Part 2




THE RELEVANCE TO WELD PROCESS CONTROL: In the nineteen nineties, Ed set the first multi-robot robot line in North America, to weld a large aluminum application as seen with ABB robots welding aluminum golf cart frames, (above photo). Ten years later, in contrast to more than 80% of the robots in the auto industry welding "carbon steel" parts, the four robots welding aluminum frames achieved much greater robot production efficiency, less down time and less weld rework.

In 2008, the robots and the MIG weld equipment have far surpassed the welding needs of today's applications, with this in mind, one can only wonder how much robot MIG weld quality and productivity improvement could be made in the auto / truck industry, if management focussed on process welding expertise as provided in Ed's robot weld process control training resources.


Ed set the robot welds on this golf cart frame and also trained
the ship yard welders on flux cored welding for this ship in Philadelphia.

 



1990s: A GREAT CONCERN WITH ROBOTS AND ALUMINUM WELDS WAS WIRE FEED ISSUES AND WIRE BURN BACKS TO THE CONTACT TIPS: TO GET THEIR ROBOT CONTRACT, CLUB CAR REQUIRED THAT ROBOT COMPANIES PERFORM A WELD TEST THAT REQUIRED A ROBOT PROVIDE 10,000 ROBOT ARC STARTS ON ALUMINUM SHEET METAL, RESULTING IN NO MORE THAN 10 WIRE BURN BACKS OR 10 WIRE FEED ISSUES WITH 0.046 ALUM WIRE.

NOTE, THIS TEST HAD TO BE DONE "WITHOUT THE USE OF PUSH PULL GUNS".

USING THE BEST PULSED POWER SOURCE (OTC) AVAILABLE) IN THE 1990s AND STILL ONE OF THE BEST PULSED UNITS AVAILABLE IN 2008, ED COMPLETED THE ROBOT MIG ALUMINUM WELD TEST. HE ACTUALLY GOT TO 7000 ARC STARTS WITHOUT A SINGLE WIRE BURN BACK. ED WAS WORKING WITH THE HIGHLY QUALIFIED ABB ROBOT PERSONNEL IN FORT COLLINS CO. USING ABB ROBOTS, A TRADITIONAL MIG GUN (NO PUSH PULL), AN OTC POWER SOURCE, AN ALCO TECH WIRE DEREELER, HARD PLASTIC LINERS AND OF COURSE AT THAT TIME HE APPLIED 35 YEARS OF MIG WELD PROCESS WELDING EXPERTISE TO THE ROBOT PROGRAM.

(Ed was the senior weld engineer for ABB Robotics Div. Fort Collins. CO).




 

Weld production efficiency can be greatly influenced
when you have robots working together

Problem with multi-robot weld cells. When one robot has a weld
issue that has to be rectified, the other 3 will not be working.

 

The robot application had four ABB robots in a single cell working together on a complex aluminum golf cart frame. No push-pull guns were utilized and the wire feed distance from the feeders to the guns was typically 20 to 30 feet. The customer was concerned that with the typical aluminum wire feed and arc start issues with aluminum that four robots working together involved some risk. To attain confidence in the project the customer requested a test phase with a robot producing ten thousand arc starts with no more than ten arc ignition issues.

I set the initial aluminum test data to ensure no weld start issues and after 7000 arc starts without a single burn back or arc ignition issue, the customer was satisfied that ABB should get the contract. I then established the robots welds
to compensate for the aluminum gage part fit and gap issues and of course provided optimum start and stop data. Each of the ABB robots produced approx. 30 to 40 welds per-frame.

[] ABB provided an automatic torch alignment system. The ABB system can make 3-D and angular calculation via its BullsEye automatic TCP calibration system.

[] The ABB Bulls Eye system automatically adjusts the TCP program to the torch, eliminating the need for touchups and minimizing down time

[] The ABB system also provided automatic error-handling capability-a necessary feature when robots are in close proximity the robots complete almost 130 welds on each frame.

[] ABB used robot I/O between all four robots. If one robot had an error, it communicated the error the other three. The other robots would then finish the weld they are doing, but will not move to the
next weld until they receive a "clear to go" signal. In the meantime, the robot with the error automatically goes to a service position where an operator checks the problem.

Programming four robots to weld simultaneously on a small frame application was a challenge easily handled by ABB. Adding to the complexity was the need to program error handling as well as welding. Each group of welds had to have its own error handler program, so developers had to keep in mind the path of each robot and make sure that it wouldn't cross the path of another robot.

[] The robots used regular MIG guns, push pull guns were not necessary.

[] For optimum wire feed, we set Alco Tech dee-reelers and hard plastic liners.




The aluminum robot production began in early 1998. Since that time, the company has produced more than 100,000 aluminum golf cart frames. Two people operate the system, one loads a fixture in one cell, while the robots are welding in the other cell. Arc on time for the 130 welds on the cart frames was approx. 6 minutes as compared with 27 minutes for the welders to manually weld the frames.

This 11 year old project, is in 2008 welding aluminum frames with multi-robots in close proximity and attaining far superior robot weld quality and production efficiency than the majority of robot "carbon steel" frame weld applications as found in global auto / truck plants.

 

 


IRRESPECTIVE OF THE "NEW" WELD APPLICATION YOU ARE WORKING ON TODAY. IT'S LIKELY SOMEONE IN THE PAST HAS PRODUCED THE WELDING RESULTS YOU ARE SEARCHING FOR.

KEEP IN MIND THAT WELD SKILLS HAVE MINIMAL IMPACT ON ROBOT WELD QUALITY AND PRODUCTIVITY. IN CONTRAST, WELD PROCESS KNOWLEDGE AND WELD EQUIPMENT / CONSUMABLE KNOWLEDGE WILL OVERCOME THE GREATEST ROBOT / AUTOMATED WELD CHALLENGES. Ed Craig 1989




ESAB / ABB Arcitec / Aluminum Weld Issues.

Robot Welds on Ford
6061 Aluminum Car Seats.



During 2000, I was requested by an engineer at VAW a tier one supplier to analyze the welding performance of their ABB robot and ESAB Arcitec welding equipment. This plant produces extruded aluminum parts. The aluminum welded car seats were for Ford. The car seats and parts required small welds which were made on thin gage 6061 aluminum.

Since the installation of the robot cells, continuous production of optimum weld quality parts has been impossible due to the issues documented in this report. Weld reject rates averaged sixty percent and the robot down time per hour averaged 20 to 30 minutes. This was one of those situations in which the ESAB welding power source selected was simply not capable for the application. For the rest of the Aluminum story click here.




There are more than 400 wrought aluminum alloys,
and over 200 aluminum alloys in the forms of
castings and ingots registered with
the Aluminum Association.



 

Wrought Aluminum Alloy Designations have 4 digits.


Aluminum Alloying Elements.
Aluminum is alloyed with a number elements to provide improved weldability, strength and corrosion resistance. The primary elements that alloy with aluminum are;

[] copper,
[] silicon,
[] manganese,

[] magnesium,
[] zinc.




Aluminum Alloys


First digit is principle aluminum alloy. First digit also describes the aluminum series. Ksi is ultimate tensile strength range.

1XXX

> 99% Aluminum

non heat treatable

10-27 ksi

2XXX

Alu - Copper approx.
2 - 10% provides strength and allows precipitation hardening. Watch for weld solidification cracking

heat treatable

27-62 ksi


3XXX

Alu-Manganese. Provides increased strength

non heat treatable

16-41 ksi

4XXX

Alu-Silicon. Reduces melting temperature, welds more fluid. When combined with magnesium provides an alloy that can be heat treated.

Both heat treatable and none heat treatable

25-55 ksi


5XXX

Alu - Magnesium. Increases strength

none heat treatable

18-51 ksi

6XXX

Alu Magnesium and Silicon
Creates a unique compound magnesium silicide Mg2Si. Allows special heat treat properties, suitable for extrusion components

heat treatable

18 - 58 ksi

7XXX

Alu- Zinc. When you add zinc copper and magnesium you get a heat treatable alum alloy of very high strength. Watch for stress corrosion cracking. Some alloys MIG weldable some not

heat treatable

32 -88 ksi

 

None Heat Treatable Aluminum Alloys. With these alloys it's possible to increase the alum strength through cold working or strain hardening. To attain the desired strength, a mechanical deformation must first occur in the aluminum structure, the deformation will result in increased resistance to strain producing both higher strength and lower ductility.

These alloys are different from "heat-treatable alloys" as the non-heat treatable alloys cannot form second-phase precipitates for improved strength. Non-heat-treatable alloys cannot achieve the high strengths characteristics of heat treatable precipitation-hardened alloys.

The absence of precipitate-forming elements in the low- to moderate-strength, non-heat-treatable alloys is beneficial from a welding perspective as many of the alloy additions needed for HEAT TREATABLE precipitation hardening, copper plus magnesium, or magnesium plus silicon can lead to hot cracking during welding. The heat affected zone (HAZ) mechanical properties are higher in not-heat treatable alloys as the HAZ is not compromised by coarsening or dissolution of precipitates.

Non Heat Treatable wrought aluminum alloys can be placed into one of four groups,

1xxx Al (Al 99% minimum purity)
3xxx Al + Mn
4xxx Al + Si (some exceptions)
5xxx Al + Mg

TIG and MIG Filler alloys used to join non-heat-treatable alloys typically come from three alloy groups:

1xxx
4xxx
5xxx

Commonly used TIG and MIG filler alloys for none heat treatable alloys include,

1100, 1188,
4043, 4047,
5554, 5654, 5183, 5356, 5556.

When MIG or TIG welding "non-heat treatable" aluminum alloys, note that the HAZ will be annealed during the weld. The none heat treatable alloys are annealed during welding in the 600-700 F, range, the time required at this temperature is short. The alum welds will have minimal impact on the transverse ultimate tensile strength of a groove weld as the annealed HAZ of the none heat treatable alum alloys will usually be the weakest area of the weld joint.

Weld procedure qualification for the none heat treat alloys is typically based on the minimum tensile strength of the alum base alloy in its annealed condition.

When welding the non-heat-treatable alloys microstructure damage will occur in the HAZ. The HAZ damage in non-heat-treatable alloys is how
ever minimal effecting both recrystallization / grain growth. In contrast with the heat treatable alloys the mechanical properties loss is extensive.

When welding all aluminum alloys, please note: To help retain the properties in the Aluminum HAZ locations, always use low to conservative TIG or MIG weld parameters, think low weld heat. Low weld heat is one of the great real world benefits of using the pulsed MIG weld transfer mode on aluminum applications.

For the none heat treatable series that require strength, the 5xxx- alloys are popular for applications where good joint strengths can be obtained in the as-welded condition without the need for post-weld heat treatment.

The 1xxx, 3xxx, and 5xxx series wrought aluminum alloys are non-heat treatable and are strain hardenable only.


 

____________________________________________________________


Heat treatable aluminum alloys attain their optimum mechanical properties through thermal controlled heat treatment.

The 2xxx, 6xxx, and 7xxx series wrought aluminum alloys are heat treatable. In contrast the
4xxx series consist of both heat treatable and non-heat treatable alloys, beware of hot
cracking with some of these alloys.

Heat treatable alloys attain their mechanical properties through thermal treatment. Solution heat treatment and artificial aging are the most common methods.

Solution Heat Treatment is the process of heating to temperatures (around 990 Deg. F). In this temperature range the alloying elements or compounds go into solution. After heating the part is quenched typically in in water. The quench produces a supersaturated solution at room temperature. Solution heat treatment is usually followed by aging.

Aging.
The precipitation of a portion of the elements or compounds from a supersaturated solution in order to yield the required properties.

Heat treatable aluminum alloys after welding. These alloys through "post heat treatment" after welding can regain the strength lost during the welding process. When post heat-treat is applied to these alloys the heat must place the alloy elements into solid solution. The second step is provide controlled cooling after the heat treatment, this produces a supersaturated solution. The third and final step in the heat treat process is to maintain the welded part at a low temperature. The time has to be long enough to allow a controlled amount of precipitation of the aluminum alloying elements.

The affect of a weld on a heat treated alum alloy HAZ is partially annealed and overaged, remember the higher the weld joules (volts - amps- travel speed) with heat treatable alloys, the lower the as welded strength of HAZ locations.

With heat treatable or none heat treatable aluminum alloys, the differences between the MIG and TIG heat affected weld zones (HAZ) and the base metal affected by the weld heat can be significant.

With none heat treatable aluminum alloys in the 1xxx - 3xxx - 4xxx - 5xxx series, the reduction of the HAZ tensile strength is typically predictable under normal weld conditions. In contrast the HAZ area strength with heat treatable alloys 2xxx - 6xxx - 7xxx can be reduced below the minimum tensile strength required for the parts when the welding heat is excessive during the weld. Higher tensile strength from the filler and reduced strength from the part influenced by the annealing effect of the weld and you have hot cracking in the HAZ of the base metal.


Alum Designations. Aluminum alloys can be classified by a temper designation.

O = Annealed,
T = Thermally treated,
F = As fabricated,
H = Strain hardened;
W = Solution heat-treated which can designated both heat treatment, or cold working aging.

Wrought aluminum alloys are alloys that are rolled from ingot or extruded. Alloys can also be divided into a cast group of alloys. Cast alloys are those used to manufacture parts from molten alloys of aluminum poured into molds. Cast alloys are precipitation hardenable but never strain hardenable. The weldability of cast alloys is affected by casting type - permanent mold, die cast, and sand. A three-digit number, plus one decimal i.e. 2xxx designates the copper cast alloys.

 

 

 



Cast Aluminum Alloy Designations:



Aluminum Casts have three digits and one decimal place (XXX.X).

XXX .X (.X - .O = casting - .1 or .2 = ingot)
If a capital letter precedes the numbers this is a modified version.

First digit of cast aluminum alloys is the principle alloy. First digit also describes the aluminum series.

1XXX

99% Min Alum

2XXX

Copper

3XXX

Silicon + Cu and or magnesium

4XXX

Silicon

5XXX

Magnesium

6XXX

Unused Series

7XXX

Zinc

8XXX

Tin

9XXX

Other Elements

Weldable grades of aluminum castings are
319.0, 355.0, 356.0, 443.0, 444.0, 520.0, 535.0, 710.0 and 712.0.

 

Aluminum Physical Properties. Lets look at how aluminum compares to steels.

[] The typical weld characteristics of steel or stainless don't apply when mig or tig welding aluminum. Aluminum has higher thermal conductivity and lower melting temperatures, both factors will influence weld solidification, weld burn through potential and warpage problems.

[] Aluminum is three times lighter than steel and yet can offer high strength when alloyed with the right elements.

[] Aluminum can conduct electricity six times better than steel and nearly 30 times better than stainless steel.

[] Aluminum provides excellent corrosion resistance.

[] Aluminum is easy to cut and form.

[] Aluminum is nontoxic for food applications.

[] Aluminum is nonmagnetic therefore arc blow is not a problem during welding.

[] Aluminum has a thermal conductivity rate five times higher than steel. The high thermal conductivity creates a great heat sink which can create insufficient weld fusion on parts over 4 mm and weld burn through issues on parts less than 3 mm. The weld fusion concerns is one reason to consider spray transfer instead of pulsed on specific alum applications.

[] Aluminum provides welds that are less less viscous which is a problem when trying to get weld fusion with the short circuit mode. Pulsed MIG is beneficial on all thin aluminum applications. The viscosity is beneficial when using spray or pulsed transfer for all position welds.

[] Aluminum has a low melting point 1,200 degrees F, this is more than half that of steel. For a given MIG wire diameter the transition short to spray weld current for aluminum is much lower than it is for steel.

 

Aluminum Descriptions.


1XXX. Minimum 99% aluminum.
This very low strength series is considered none-heat treatable and is used primarily for bus bars and some pipe and chemical tanks. This alloy provides superior corrosion resistance. Alloys with purity levels greater than 99,5% are used for electrical conductors (for example alloy 1350). 1XXX series are easily welded with 1100 and 4043 alloys.

2XXX. Alu-Copper provide approx. 2 to 6% Cu with small amounts of other elements. The Cu increases strength and enables precipitation hardening. The 2XXX series is mainly used in the aerospace industry. Most of the 2XXX alloys have poor weldability due to their sensitivity to hot cracking. These alloys are generally welded with 4043 or 4145 series filler electrodes. These filler metals have low melting points which help reduce the probability of hot cracking. Exceptions to this are alloys 2014, 2219 and 2519, which are readily welded with 2319 filler wires. Hot cracking sensitivity in these Al-Cu alloys increases as copper is added up to 3% and decreases when the copper is above 4.5% Be wary of Alloy 2024 as it is crack sensitive.

3XXX. Alu-Manganese when added to aluminum produces a moderate strength, none-heat treatable series typically used for radiators, cooking pans, air conditioning components and beverage containers and storage equipment. The 3XXX series is improved through strain hardening which provides improved corrosion properties and improved ductility. Typically welded with 4043 or 5356 electrode, the 3XXX series is excellent for welding and not prone to hot cracking. The moderate strength of this series prevent these alloys from being utilized in specific fabrication or structural applications.

4XXX. Alu-Silicon reduces melting temperature improves fluidity. The most common use is as a welding filler material. The 4xxx-series alloys have limited industrial application in wrought form. If magnesium added it produces a precipitation hardening, heat treatable alloy. The 4XXX series has good weldability and can be a non-heat-treatable and heat treatable alloy. Used for castings, weld wires. The 4xxx wires are more difficult to feed than the 5xxx series.

5XXX. Alu-Magnesium increases mechanical properties through solid solution strengthening and improves strain hardening potential. These alloys have excellent weldability with a minimal loss of strength. The 5 XXX series has lower tendency for hot cracking. The 5XXX series provide the highest strength of the nonheat-treatable aluminum alloys. These alloys are used for cryo vessels, chemical storage tanks, auto parts, pressure vessels at elevated temperatures, cryogenic vessels as well as structural applications, railway cars, trailers, dump trucks and bridges because of the corrosion resistance. 5xxx looses ductility when welded with 4xxx series fillers due to formation of Mg2Si.

5xxx Series and Weld Crack Sensitivity: The 5xxx typically while welding with or without filler metal have low crack sensitivity. Usually the filler metal will have a little more Mg than the base metals being welded. Be wary of 5052 especially if TIG welding without a filler metal, use a high Mg filler like 5356 for the 5052 alloy. All aluminum concave fillet welds and concave craters are sensitive to hot cracks.

6XXX. Alu-Magnesium & Silicon (magnesium-silicides) combine to serve as alloying elements for this medium-strength, heat-treatable series. 6XXX are principally used in automotive, pipe, structural, railings and extruded parts. This series can be prone to hot cracking, but this problem can be overcome by the correct choice of joint and filler metal and weld procedures that minimize weld heat input. This series can be welded with either 5XXX or 4XXX series, adequate dilution of the base alloys with selected filler alloy is essential. 4043 electrode is the most common filler metal for this series. Be wary of liquation cracking in the HAZ when using specific 5xxx alloys. See Liquation cracking above notes.

6xxx Crack Sensitivity:
As many of the 6xxx alloys have 1.0% magnesium silicide, these alloys are crack sensitive. Avoid welding without filler metal and do not use a 6xxx material as a filler metal. Using 4xxx or 5xxx filler metals reduces crack sensitivity as long as sufficient weld metal is added and good weld dilution occurs with the 6xxx base metals. Avoid weld joints in which minimal weld dilution occurs, a vee prep is superior to a square groove. All 6xxx aluminum applications that have concave welds and concave craters are sensitive to hot cracks.

7XXX. Alu-Zinc when added to aluminum with magnesium and copper permits precipitation hardening and produces the highest strength heat-treatable aluminum alloy. These alloys are primarily used in the aircraft industry, armored vehicles and bike frames. The weldability of the 7XXX series is compromised in higher copper grades, as many of these grades are crack sensitive (due to wide melting ranges and low solidus melting temperatures.) And susceptible to stress corrosion cracking. Grades 7005 and 7039 are weldable with 5XXX fillers.

7xxx Crack Sensitivity:
The 7xxx Al-Zn-Mg alloys (typically welded with 5356 avoid 4043) resist hot cracking better than the 7xxx Al-Zn-Mg-Cu alloys.

8XXX. Other elements that are alloyed with aluminum (i.e. lithium) all fall under this series. Most of these alloys are not commonly welded, though they offer very good rigidity and are principally used in the aerospace industry. Filler metal selection for these heat-treatable alloys include the 4XXX series.

 

 


Panasonic weld equipment issues
and lack of aluminum welding process expertise:







The company I visited welds 6xxx series, extruded aluminum, thin gage parts. They had purchased a Panasonic VR OOGAL 11robot, with a Panasonic 350 amp Panastar RA 350 pulsed power source. For the welds they used an 0.046, 4043 wire and argon. The MIG wire spool was mounted on top of the robot, and they used a regular four-drive roll feeder with a water-cooled gun. The problem robot welds were short lengths, 5/8 to ¾ long. The robot welds are made on aluminum square tubes 0.070 thick. The 6xxx tubes are welded to a thicker alum part 3/16 thick. Since they purchased the robot the completed welds never look consistent over their short lengths. All the thin tube welds were made with the same weld data, yet in the same locations on the parts, some welds look fluid while other welds look cold. Most of the welds ended up with a black and dirty appearance yet the push gun angle is correct. These welds caused so many issues the company was ready to give up the robot and go back to manual TIG. For the rest of the story, click here.

 


A Combination of Balance Wave Control Power Source and
TIP-TIG
Wire Feeder is the ultimate tool to attain consistent
optimum aluminum welds with minimum weld skills.



Aluminum Welding Tips and Information

 

Aluminum alloys provide unique physical properties.

Weight. Aluminum is three times lighter than steel and yet aluminum can provide higher strength when alloyed with specific elements.

None Magnetic.
Since aluminum is nonmagnetic, arc blow is not a problem during aluminum welding.

Thermal Conductivity. With a thermal conductivity rate that is five to six times higher than steel and the aluminum welds watch out for lack of weld fusion especially at the weld starts. With alum being more sluggish and less fluid, aluminum can be welded in all positions with spray and pulsed with relative ease. In contrast to steel the high conductivity of aluminum acts as a heat sink making weld fusion and weld penetration more difficult to achieve on parts > 4 mm.. However on thin parts, the rapid build up of heat in the alum parts can add to high weld fluidity and weld burn through potential.



 

 

 

Aluminum Porosity and Hydrogen. When MIG or TIG welding aluminum, the weld decision maker should always be aware that this is one of the metals most susceptible to porosity.Hydrogen dissolved in the liquid weld metal will try to escape as the aluminum solidifies and the trapped hydrogen will result in weld porosity which is often extensive. The main cause of porosity in aluminum welds is the absorption of hydrogen in the weld pool which forms gas pores in the solidifying weld metal. The most common sources of hydrogen are hydrocarbons and moisture from contaminants on the aluminum base metal and on the filler wire surface. Also water vapor from the MIG or TIG shielding gas will provide the same results.

Hydrogen cracking is common with carbon steels but hydrogen cracking will not occur with aluminum. Hot cracking or solidification cracking is a primary cause for aluminum cracks.


ALUMINUM Welds and Solidification Cracking.

Alum Solidification cracks can happen due to thermal expansion and contraction during the aluminum these factors generates high stresses sometimes tearing the weld apart..


Common causes of alum solidification cracks.


[a] incorrect choice of alum weld consumable.

[b] Concave welds, undersize welds, and welds with insufficient weld throat. (The weld throat depth must be sufficient to compensate for the weld contraction stresses).

[c] Weld joints too rigid.

[d] Poor weld weld geometry.

[e] Poor weld joint design. Weld restraint and weld stresses can be reduced by focussing on the weld edge prep, the weld sequence.

[f] Excess weld heat, watch weld pass sequence and on multi-pass welds consider interpass temperature control.

Solidification cracking is reduced with the selection of crack-resistant filler metal like the 4xxx and 5xxx filler metal. Be wary when choosing the filler metal to specifically reduce weld cracking, as the weld metal may provide lower strength than the parent metal and will not respond to heat treatment if applied.

ALUMINUM Liquation Cracking. In contrast to hot cracking which occurs in the weld, while MIG or TIG welding aluminum liquation cracking will occur in the heat affected zone (HAZ). With liquation cracking low melting point films are formed at the grain boundaries and these films (liquid elements)cannot withstand the contraction stresses during the weld metal solidification. Heat treatable alloys, like the 6xxx and 7xxx series are sensitive to liquation cracking. To reduce the potential for liquation cracking, consider a weld wire with a lower melt temperature than the parent metal. With alloy 6061 - 6082, liquation cracking can occur in the partially melted zone when a weld with good dilution is made with 5356 or similar filler metal is utilized. In contrast when welding the same alloys with 4043 liquation cracking should not occur.

 

 



All it takes is a little TIG - MIG weld process knowledge
to not produce welds like this.




Aluminum Oxides. Aluminum will combine with oxygen to form an aluminum oxide layer. This layer will form instantly as the aluminum surface is ground or machined. The aluminum oxide layer while very thin can also be very porous. The oxide layer will readily trap moisture, oil, grease and other materials adding to the potential for hydrogen pickup. The aluminum oxide layer provides excellent corrosion resistance, however this layer must be removed before welding as it prevents fusion due to its higher melting point (3700 degrees F). The weld arc gas molecules, the fore hand (push) technique, mechanical cleaning, wire brushing, solvents and chemical etching and voltage control are used for the oxide removal. One of the best practices to attain clean alum MIG welds is to use the lowest possible voltage which assures a short arc length, and a concentrated plasma which is beneficial for the oxide removal.

Aluminum alloys that are difficult to weld.

Alloys that may be sensitive to hot cracking are found in the 2xxxseries, alum-copper and in the 7xxx series alum-zinc.

With the 2xxx series hot cracking sensitivity increases with Cu < 3% and decreases with Cu > 4.5%. Avoid weld practices that promote high heat input as grain boundary segregation cracking potential.

7xxx alloys that contain Al-Zn-Mg like 7005 resist hot cracking and have better mechanical weld properties than Al-Zn-Mg-Cu alloys like 7075 that contain small amounts of Mg and Cu
which extend the coherance range increasing the crack sensitivity. Zirconium is added to refine grain size and reduce crack potential. Electrode 5356 is often recommended for this group as the magnesium helps prevent cracking. The 4043 electrode would provide excess Si promoting brittle Mg2Si particles in the welds.

Be careful when welding dissimilar alum alloys as extending the coherence range increases the crack sensitivity. When welding alloys that do have good weldability like welding a 5xxx alloy to a 2xxx base alloy or a 2xxx filler on a 5xxx alloy and vice a versa you can end up with high Mg and Cu and increase the coherence range increasing the crack sensitivity.


F
ive Common Aluminum MIG Filler Welding Metals:

5356 - 4043 - 1100 - 5556 - 4047

Usually the filler metal selected should be similar in composition to the base metal alloy for example a 1XXX filler wire for welding 1XXX - 3XXX-series base metal alloys. Special consideration is however required when weldability is an issue. Weldability of non-heat-treatable aluminum alloys should be measured in resistance to hot cracking and porosity potential. Hot cracking issues are encountered when welding with alloys sensitive to cracking, alloys subject to excess heat or parts that are highly constrained.

Cracking issues can occur when low strength weld alloys like 1XXX are used to join 5XXX alloys (or vice versa) or when welding dissimilar metals with different strengths. The best filler metals when hot cracking occurs is to use 4xxx fillers.


When considering an aluminum MIG filler metal make sure you ask the right filler metal questions.



What's the best alum filler for "corrosion resistance"?

What's the best alum filler to "match the color" of the base metal?

What's the best alum filler for carrying "high weld current"?

What's the best alum filler for "good weld crack resistance"?

What's the best alum filler for the "desired strength"?

What's the best alum filler for "high temp or low temp service"?

Weld mechanical properties such as yield, tensile strength and elongation are affected by the choice of aluminum base and filler alloys.

With groove welds, the heat affected zone (HAZ) dictates the strength of the joint. The non-heat-treatable aluminum alloys HAZ will be annealed and their HAZ will be the weakest point.

Heat-treatable alloys require much longer periods at annealing temperatures combined with slow cooling to completely anneal them so that weld strength is less affected. When welding alum please remember that preheating, excess interpass temperatures and and excess weld heat from over sized welds, slow weld speeds and weaving all increase temperature and time at temperature all can influence the strength levels that will be attained.

In contrast to groove welds the fillet weld strength is dependent on the composition of the filler alloy used to weld the joint. For example the selection of 5XXX instead of 4XXX can provide twice the weld strength.

 


When to use either
4043 or 5356 filler wire?

 

4043 aluminum filler wire is an aluminum wire with 5% silicon. This wire was developed for welding the 6xxx series aluminum alloys. 4043 may also be used to weld the 3xxx series or 2xxx alloys. 4043 is also used for welding castings.


[] 4043 has a lower melting point and provides more weld fluidity than 5xxx series filler alloys. 4043 will provide cleaner "less black soot because it doesn't contain magnesium.

[] 4043 is often preferred by welders as it provides better weld wetting, smoother weld surface more stable transfer and is also less sensitive to weld cracking when welding the 6xxx series base alloys.

[] 4043 provides more weld penetration than 5356, however the 4043 will produce welds with less shear strength and ductility than those made using 5356.

[] 4043 is used for applications when the service temp above 150 F, in contrast 5356 is not suited to applications where prolonged heat is applied.

[] 4043 is not well suited for welding Al-Mg 5xxx alloys and should not be used with 5xxx alloys with > 2.5% Mg, alloys such as 5083, 5086 or 5456 as excess magnesium-silicide (Mg2Si) can develop in the weld structure decreasing ductility and increasing crack sensitivity. (One exception to this 4043 rule is when welding the 5052 alloy which has a low magnesium content.)

[] When shear strength is the concern consider 5xxx rather than 4xxx filler metals.

[] As welded 4043 will provide lower ductility than 5356, this is important if you are shaping the welded part after welding to remember this fact.

[] For MIG wire feedability note the 4043 or 1100 are softer than 5356 so expect more wire feed issues.

 

5356 wire is an aluminum wire with 5% magnesium. This is the most common aluminum filler wire due to superior strength, ductility and superior MIG wire feedability. 5356 was developed to weld the 5xxx structural alloys and also the 6xxx series extrusions. Do not use the 5356 on castings as they are high in silicon. 5356 is not suited to weld applications in which the service temperatures exceed 150 degrees Fahrenheit (65 degrees Celsius). The formation of Al2Mg at elevated temperatures at the grain boundaries makes the alloys prone to stress corrosion. For components that will be anodized after welding, 5356 is recommended for the best color match, in contrast 4043, will turn black when anodized.

Aluminum Weld Strength and Weld Heat Considerations:

As mentioned, typically the resulting HAZ of a groove weld will determine the strength of the joint and usually a variety of filler alloys will match or exceed this strength requirement. However, there are many other factors for consideration when welding the heat treat or non-heat treatable alloys.

Heat treatable alloys require a specific time at temperature to fully reduce their strength. The strength reduction in the heat treatable alloy may be minimal or extensive during the welds, defendant on the weld procedures and technique and fixtures utilized. The amount of strength loss due to weld heat is influenced by both time / temperature. Faster weld speed or smaller welds produce less weld heat in the weld area. Fixtures that provide heat sinks lower the weld heat input. The lower the weld heat the higher the as welded strength.

The following can add unnecessary weld heat and require consideration on the influence of weld heat on aluminum alloys;

[1] lack of interpass weld temperature controls on, multi-pass welds.
[2] excess preheating,
[3] slow weld speeds,
[4] wide (8 mm) weld weaves,
[5] oversized welds,(>6 mm fillets),
[6] welding thin parts or many welds concentrated is a small area,
[7] unnecessary high weld current and voltage.


Shear or Tensile Strength. In contrast to aluminum groove welds, the fillet weld strength is mostly dependent on the composition of the alum filler alloy used. The fillet joint strength is based on shear strength which can be affected considerably by filler alloy selection.

When welding alum structural applications and considering the 5xxx series or 4xxx series filler metals, the tensile strength of groove welds differences may be minimal. However serious consideration is required when considering the shear strength of aluminum "fillet welds". The approx. transverse shear strength of 4043 is around 15 ksi while the shear strength of 5356 is approx. 26 ksi. The bottom line the 5356 provides superior ductility and shear strength.

WIRE TYPE AND FILLET WELD SIZE: Alcotec reports that tests have shown that a required shear strength value in a fillet weld in 6061 base alloy required a 1/4 inch (6 mm) fillet weld with 5556 filler compared to a 7/16. (11 mm) fillet with 4043 filler alloy to meet the same required shear strength. This can mean the difference between a one run fillet and a three run fillet to achieve the same strength.

Ductility and alum welds may be a consideration if forming is to be performed after welding or if the alum weld is going to be subjected to impact loading. Also ductility should be given consideration when bend tests are applied during weld procedure qualification.

In contrast to the 5xxx series, the 4xxx series filler alloys provide lower weld ductility, this is addressed with special requirements within the code or standards relating to the weld test sample thickness, bending radius, and material condition.

Corrosion Resistance: Most aluminum base alloy filler alloy combinations provide satisfactory protection for against general exposure to the atmosphere. One filler alloy developed for use within a specific corrosive environment, is the 5654 alloy. The 5654 alloy was developed to weld storage tanks that contain hydrogen peroxide. The difference in alloy performance can vary based upon the type of exposure. Filler alloy charts ratings are typically based on fresh and salt water only. Corrosion resistance can be a complex subject when looking at service in specialized high corrosive environments, and may necessitate consultation with engineers from within this specialized field. Good contact Alcotec.

Service Temperature: Stress corrosion cracking (SCR) is an undesirable condition which can result in premature failure of a welded component. One condition which can assist in the development of SCR is Magnesium segregation at the grain boundaries of the material. This condition can be developed in the Mg alloys of over 3 % through the exposure to elevated temperature. When considering service at temperatures above 150 Deg F, we must consider the use of filler alloys which can operate at these temperatures without any undesirable effects to the welded joint. Filler alloys 5356, 5183, 5654 and 5556 all contain in excess of 3 % Mg, typically around 5%. Therefore, they are not suitable for temperature service. Alloy 5554 has less than 3 % Mg and was developed for high temperature applications. Alloy 5554 is used for welding of 5454 base alloy which is also used for these high temp applications. The Al – Si (4xxx series) filler alloys may be used for some service temperature applications dependent on weld performance requirements. More info contact Alcotec.

Color Match After Anodizing: The color of an aluminum alloy when anodized depends on its composition. Silicon in aluminum causes a darkening of the alloy when chemically treated during the anodizing process. If 5% silicon alloy 4043 filler is used to weld a 6061 application, and the welded assembly is anodized, the weld becomes black and is very apparent. A similar weld in 6061 with 5356 filler does not discolor during anodizing, so a good color match is obtained.

Post Weld Heat Treatment: Typically, the common heat treatable base alloys, such as 6061-T6, lose a substantial proportion of their mechanical strength after welding. Alloy 6061-T6 has typically 45,000 PSI tensile strength prior to welding and typically 27,000 PSI in the as-welded condition. Consequently, on occasion its desirable to perform post weld heat treatment to return the mechanical strength to the manufactured component.

If post weld heat treatment is the option, it is necessary to evaluate the filler alloy used with regards to its ability to respond to the heat treatment. Most of the commonly used filler alloys will not respond to post weld heat treatment without substantial dilution with the heat treatable base alloy. This is not always easy to achieve and can be difficult to control consistently. For this reason, there are some special filler alloys which have been developed to provide a heat treatable filler alloy which guarantees that the weld will respond to the heat treatment.

Filler alloy 4643 was developed for welding the 6xxx series base alloys and developing high mechanical properties in the post weld heat-treated condition. This filler alloy was developed by taking the well-known alloy 4043 and reducing the silicon and adding .10 to .30 % magnesium. This chemistry introduces Mg2Si into the weld metal and provides a weld that will respond to heat treatment.

Filler alloy 5180 was developed for welding the 7xxx series base alloys. It falls within the Al-Zn-Mg alloy family and responds to post weld thermal treatments. It provides very high weld mechanical properties in the post weld heat-treated condition. This alloy is used to weld 7005 bicycle frames and will respond to heat treatment without dilution of the thin walled tubing used for this high performance application. Other heat treatable filler alloys have been developed including 2319, 4009, 4010, 4145, 206.0, A356.0, A357.0, C355.0 and 357.0 for the welding of heat treatable wrought and cast aluminum alloys.

Work Hardening is used to produce strain-hardened tempers in none-heat treatable alum alloys. (Increases strength). This is influenced by mechanical energy leading to deformation. As the deformation occurs the alum alloy becomes stronger, harder and less ductile.


Precipitation Hardening
(artificial aging). Precipitation heat treat precedes solution heat treat. Hold alloys at a specific temp long enough to allow constituents to enter into solid solution, then cool rapidly to hold constituents to remain in solid solution Artificial aging follows.The alloy is reheated to a lower temp and holding for a specific time. This heat treat produces superior mechanical properties. Please note on the heat treatable alloys that have undergone this treatment, the weld metal heat will change the mechanical properties in both the HAZ and base metal.

 

 

Aluminum Filler Metal Information:
Aluminum
Filler
International SpecsChemistryMelt
Temp
Yield Tensile

Electrode
1050A

ISO / Germany A199.5
France A5
Italy P-AP5


  
 
 

Electrode
1100

ESAB OK 18.01
Conarcao A400S
Pacweld 421 AA

Al 99% - Mn0.05 Cu 0.05 - 0.2
Si - Fe0.95
Zn 0.10
1190 to 1215F
643 to 657C

5 ksi
34MPA

13 ksi
90 MPa

Electrode
1100 - H12

   

15 ksi


16 ksi

Electrode
1100 - H14

   

17 ksi

18 ksi

ER filler 1100 used to weld all 1XXX alloys plus 3003
and 5005 alloys

Electrode
1188

UNS A91188Al 99.8%
Si 0,06, Fe 0.06
Cu 0.005,
Mn 0.01,
Zn 0.03. Ti0.01

1215F
657C

  

Electrode
2319

UNS A 92319
used for Al lithium aircraft alloy 2090

2319 is heat treatable good strength ductility on Al Cu Casts

don't use 2319 on 5XXX
Cu 5.8 - 6.8
Si 0.2 / Fe0.3
Mn0.2-0.4
Mg 0.02
Zn 0.1
Ti 0.1 - 0.2
1010 to 1190F

543 to 643C
 

2319 used on 2219 2014 plus alum copper cast alloys

Dont use on 5XXX

ER4XXX TIG - MIG ALUMINUM ELECTRODES.

ER 4043 - 4047
Moderate stren
gth good corrosion resistance.
(Less strength than 5356)
ER 4043 - 4047 Low sensitivity to cracking while welding
ER 4043 - 4047 Lower weld ductility than 1XXX - 2XXX - 5XXX
ER 4043 - 4047 Can weld 1XXX - 3XXX - 6XXX 2014 / 2219 / 005 /5052 / 7005 /
7039 Al - Si and Al - Si - Mg casts

Electrode
4043

Germany ISO S - ALSi5
Italy S-AlSi5
France A- S5

"don't" use to weld high Mg 5XXX 5083 - 5086- 5456

ESAB 0K18.04
Packweld 425/AA
Thysen UnAlSi5
Century 331 400
Conarco A408

Si 4.5 - 6
Fe 0.8, Cu 0.3
Mn 0.05
Mg 0,05, Zn 0.1
Ti 0.2
1155F
623 C

10 ksi
69 Mpa

Moderate strength good corrosion resistance

Low sensitivity to cracks while welding

Lower ductility than 1XXX
2XXX
5XXX


21 ksi
145 Mpa

Can use on 1XXX
3XXX
6XXX
2014
2219
5005
5052
7005
7039
Al-SI + Al Si Mg casts

Electrode
4043 - 18

   

39 ksi
270 MPa

41 ksi
285 MPa

On thin alum sheet 4047 is used as an alternative to 4043

Electrode
4047

Germany ISO
S- AlSi12
Italy S-AlSi12
France A-S12
Si 11 - 13
Fe 0.8, Cu 0.3
Mn 0.15, Mg 0.1
Zn 0.2
1050F
565C
 

Moderate strength good corrosion resistance

Low sensitivity to cracks while welding

Lower ductility than 1XXX
2XXX
5XXX

Can use on 1XXX
3XXX
6XXX
2014
2219
5005
5052
7005
7039
Al-SI + Al Si Mg casts. Faster feeeze than 4043 can prevent formation of crater cracks

Electrode
4145

Si 9.3 - 10.7
Fe 0.8
Cu 3.3 -4.7
Mg/Mn/Cr 0.15
Zn 0.2
970F
 

Low sensitivity to weld cracks on 2XXX

Good for
Al - Cu
Al -Si- Cu
cast alloys responds to heat treat

can repalce 4043 4047 will result in lower ductility

ER 4145 Low sensitivity to weld cracking on 2XXX alloys
ER 4145 Good for Al - Cu Al Si Cu Cast Alloys. Responds to heat treat. ER 4145 Can replace ER 4043 4047, will however have lower ductility
.

Electrode
4643

Si 3.6 - 4.6
Fe 0.8, Cu 1.1
Mg 0.1 - 0.3
Zn 0.1, Mn 0.05
Ti 0.15
1065 to 1175F
573 to 635C
4043 is a goodchoice for the welding of heat-treatable alloys especially the 6XXX series. 4043 has a lower melting point and more fluidity than the 5XXX series filler alloys. 4043 has good welability. 4043 wires are also less sensitive to weld cracking with the 6XXX series base alloys. 4043 is suitable for sustained elevated temperature service, above 150 deg F (65 deg C).


KEEP THE ALUM CLEAN BEFORE WELDING. Aluminum has a great affinity for hydrogen, which can be picked up from many sources, dirt, paint, moisture, markers, lubricants, etc. All mentioned can form hydrocarbons causing serious porosity which can weaken the weld.

WELD POROSITY IS MORE OF A CONCERN WITH ALUMINUM THAN IT IS WITH STAINLESS OR STEEL. THE REASON STAINLESS AND CARBON STEEL TYPICALLY HAVE MUCH GREATER YIELD STRENGTH.

To clean aluminum, consider degreasing solvents and clean stainless steel brushes. Caution some grinding wheels will contaminate aluminum, (use wheels recommended for alum). Also on heat treatable alloys, plasma gouging and cutting can cause micro cracks on component edges, (remove edges with grinder)

ER5XXX TIG-MIG ELECTRODES:

ER 5XXX Higher strength than other aluminum electrodes
ER 5XXX used to weld 5XXX - 6XXX - 7005 alloys
Don't use ER5XXX filler on 2XXX alloys
ER 5XXX Higher Mg Higher strength and crack sensitivity decreases
ER 5XXX Pre heat and interpass max temp 150F 65C

Electrode
5056

ISO/Germany AlMg5
France A-G5MC
Italy P-AG5
    

Electrode
5083

ISO /Germany
AlMg4.5Mn
France A-G4,5MC
   

Electrode
5154

ISO AlMg3.5
Germany AlMg3
France A-G3C
   

Electrode
5183

Germany S-AlMg4.5Mn
France AlMg4.5Mn
Mg 4.3 - 5.2
Si/Fe 0.4
Cu 0.1
Mn 0.5 -1
Cr 0.05 -0.25
Zn 0.25
Ti 0.15
1075 to 1180F
579 TO 637 C
 Dont use on high temp applications
5183 is for welding high magnesium alloys to meet higher tensile strength requirements than 5356.
Use on 5083 and 5654 base materials when required tensile strengths are >40,000 psi (276 MPa) or greater. Typical applications are in the marine and cryogenic industries, and high strength structural aluminum fabrication.


REDUCE THE ALUMINUM "BLACK OXIDES"

The black soot that frequently occurs with MIG aluminum welds, is a combination of aluminum and magnesium alloys that combine with oxygen and form oxides that appear black. The oxides that form have a lower boiling point than the arc temperature, they evaporate and condense on the weld or HAZ area. Expect more soot from higher magnesium alloys. For example the common 5356 filler metal can provide more soot than E4043 filler metal.

Excess soot is usually an indication of weld porosity issues. The soot can caused and corrected by the following.

[A]
INSUFFICIENT WELD ENERGY. TO ASSIST IN THE REMOVAL OF THE ALUM SURFACE OXIDES. INCREASE WELD CURRENT / WIRE FEED OR DECREASE WIRE SIZE FOR MORE CURRENT DENSITY.

[B] ARC LENGTH THAT IS TOO LONG. INSUFFICIENT PLASMA ARC ENERGY CONCENTRATION FOR THE SURFACE OXIDE REDUCTION.
REDUCE THE ARC LENGTH BY LOWERING WELD VOLTS.

[C] INCORRECT WELD GUN ANGLE. ENSURE THE FOREHAND (PUSH) TECHNIQUE IS USED TO DIRECT THE ARC TO BREAK UP THE ALUM OXIDE SKIN IN FRONT OF THE WELD. BACK HAND (PULL) WILL PROVIDE THE WORST RESULTS.

[D] INSUFFICIENT GAS COVERAGE. USE 40 TO 60 CUFT/HR AND ENSURE THE GAS CUP IS A LITTLE WIDER THAN THE WELD AND HEAT AFFECTED ZONE WIDTH. IF USING HELIUM ENSURE HELIUM FLOW METER IS USED AND ENSURE HELIUM FLOW RATE IS A MINIMUM OF 45 CUFT/HR

[E] WELD SPEED TO FAST. MAY NOT ALLOW ADEQUATE BREAKUP OR REMOVAL OF ALUMINUM SURFACE OXIDES.

[F] ALUM SURFACE CONTAMINATED. NEEDS CLEANING.

[G] CYLINDER GAS CONTAMINATED, TYPICALLY DUE TO POOR DISTRIBUTOR GAS FILLING PRACTICE WHICH LEAVES EITHER CO2, OXYGEN OR MOISTURE IN THE CYLINDERS.

Electrode
5356

Germany France S - AlMg5
Italy S-ALMG5

ESAB OK 18.15
Pacweld 430A
Conarco A404
Thyssen UnAlMg5
Mg 4.5 - 5.5
Cu 0.1
Ti 0.06 - 0.2
Cr/Mn 0.05-0.2
Zn 0.1
Si 0.25 / Fe 0.4
1180F
637C

Dont use on high temp applications. 5356 is a great general purpose filler alloy designed for the welding of 5XXX series alloys when <40,000 psi (276 MPa) tensile strength is required.

5183 and 5556 sometimes used as an alternative to 5356

Electrode
5454

ISO AlMg3Mn
Germany AlMg2.7Mn
France A-G2.5MC
    

Electrode
5554

Italy S-AlMg3MnCu 0.1,
Mn0.05-1
Mg 2.4 - 3
Cr/Ti 0.05-0.2
Zn 0.25
1115 to 1195F
601 to 646C
  

Electrode
5556

ISO -
AlMg5.2MnCr
Germany
AlMg5

ESAB OK 18.6
Pacweld 431 AA
Conarco A4045
Mg 4.7 - 5,5
Si 0.25, Fe0.4
Cu 0.1,
Mn 0.5 - 1
Cr 0.05 -0.2
Zn 0.25
Ti 0.05 -0.2
1180F
637C
 

5556 weld deposits will provide matching tensile strengths for the 5XXX alloys, such as 5083 and 5654. Contains increased amounts of magnesium and manganese. Dont use on high temp applications

Electrode
5654

Mg 3.1 - 3.9
Cu 0.05,
Mn0.01
Cr 0.15-0.35
Ti 0.05 -0.15
Zn 0.02
dont use on high temp applications

    



ALUMINUM WELD TIPS AND DATA:

THIS ALUMINUM MIG WIRES A BARGAIN.

If you get your aluminum MIG wire at a bargain price, its likely you will have weld consequences. To test an aluminum MIG wire, take two 1/4 alum plates, six inches long. Start a 3/16, horizontal fillet weld approx. one inch from the end of the plate. Make the weld is four inches long. Don't weave use fore hand. After the weld has cooled, put welded plate in vice and use hammer to fold the plates in on the weld.

In contrast to steel welds, a good, alum weld with proper side wall fusion should break in most cases in the weld metal. Examine the broken weld surface for porosity. Clean looking, small pore porosity is found in the best of aluminum welds. Blackish looking small porosity often results from lubricants from the material surface. Small gray, oxidized weld porosity often results from air trapped in the joint or oxygen from the gas cylinders or lines. Extensive shiny porosity may be an indication of moisture pickup. Ensure synthetic impermeable hoses are used for your aluminum MIG gas delivery rather than neoprene or rubber hoses.

Weld porosity can be blamed on many materials that can contaminate both the weld wires and base metals. With aluminum, hydrogen is the prime cause. The bottom line keep the plates clean and at the ambient shop temperature. If necessary for your application grind the weld edges. Provide a protective cover for the alum weld wires. When the weld wires are not in use store in clean dry area. Good manufacturers of aluminum MIG wires will use extensive manufacturing controls to ensure you have a clean consistent MIG wire. There is a price to be paid for this weld wire quality. Compare your bargain priced aluminum wire with a quality and consistent product from a company like Alcotec.

 

 

Aluminum, Oxidation, Hydrogen and Porosity.
Aluminum has a high maximum solubility for hydrogen atoms in the liquid form and a low solubility at the solidification point.

Hydrogen dissolved in the liquid weld metal will try to rise out of the weld during the aluminum solidification. Some hydrogen gas pores will be trapped and porosity will occur.

Aluminum combines with oxygen to form an aluminum oxide layer. This micro surface layer will form instantaneously if the oxide is removed by machining or grinding. The oxide layer is porous and can easily trap moisture, oil, grease and other materials. The aluminum oxide layer provides excellent corrosion resistance, but must be removed before welding as it prevents fusion due to its much high melting point point than the aluminum alloy .

Arc polarity, plasma molecular action, mechanical cleaning, solvents and chemical etching are all used to attack the oxide layer. When MIG welding if the layer is not removed sufficiently a black soot will appear either side of the weld. To eliminate the soot, first try to lower the arc length (voltage) as this makes the MIG plasma more dense which provides a more concentrated plasma cleaning action.

The majority of aluminum weld porosity results from entrapped hydrogen gas in the weld pool. Hydrogen is highly soluble in molten aluminum. Hydrogen can be derived from many sources.

[a] Hydrogen from base metal contaminates, hydrocarbons, lubricant, oils dirt, grease, moisture, paints and compressed air and contaminates from pneumatic cleaning tools or cleaning brushes.

[b] Hydrogen from lubricant contaminates on the alum weld wire surface.

[c] Hydrogen from moisture, water leaks in water cooled torches. Water from the gas cylinders. Water from the porous, hydrated, alum oxide layer on the base metal surface.

[d] Hydrogen that results from high humidity, condensation on parts and weld wires.

[e] Hydrogen that results from contaminates from grinding wheels.


To minimize hydrogen and weld porosity potential consider, cleaning, degreasing, stainless wire brushes or carbide wheels to remove the oxide surface. Remember you can always find porosity in the alum weld, the real question is how much is acceptable and what inspection and weld process control method will be used to control the porosity.

To reduce aluminum weld porosity potential, slow down the weld solidification rate to allow the hydrogen to exit. Reduce alum weld porosity with the following 11 points.

[1] To remove the alum surface oxide consider a die grinder (>30,000-rpm) rotary, coarse carbide file. An effective cleaning solution is acetone, beware highly flammable..

[2] Increasing weld parameters, with MIG increase the wire feed rate.

[3] Increase weld size.

[4] Avoid weaves.

[5] Slow down weld travel speed.

[6] Use smaller diameter MIG wires.

[7] Evaluate the weld procedure so that weld heat and weld sequence is used as a tool for porosity reduction.

[8] Use lowest possible MIG weld voltage. Low weld voltage results in short arc lengths which create more energy in the arc plasma providing improved arc cleaning action of the surface alum oxides.

[9]Use a higher energy gas mix like 60 helium - 40 argon. The helium requires higher weld voltage. The 60 helium mix is superior to the common 75 helium 25 argon mix, as the the higher argon content helps stabilize the arc and provides superior weld cleaning action.

[10] Don't use MIG wire wipes clipped on the wire.

[11] Don't use anti spatter within 2 inches of the weld. If you know how to set a weld you would not use anti-spatter.




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Continue TIG WELDING ALUMINUM Section 2.

 



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