In the nineteen nineties, Ed set the first multi-robot, 4 robot cell in
North America, to weld an aluminum part as seen in the above photo
IN 2008, MIG WELDING ALUMINUM IS A MORE SIMPLE TASK THAN MIG WELDING CARBON STEELS. WITH CARBON STEELS WE STILL HAVE WELD WIRE SIZES AND WELD TRANSFER MODE CHOICES. SHORT CIRCUIT, SPRAY AND PULSED OFFER UNIQUE WELD BENEFITS FOR CARBON STEELS. WITH ALUMINUM WELDS YOU SIMPLY PICK AN 0.046 WIRE AND USE ONE OF FOUR PULSED SETTINGS FOR ALL ALUMINUM WELDS.
Ed set the aluminum robot welds on this golf cart frame and trained
the ship yard welders on flux cored welding for this ship in Philadelphia
ALUMINUM GOLF CARTS:
1990s: THE GREAT CONCERN WITH ROBOTS AND ALUMIUM WELDS WAS WIRE BURN BACKS TO THE CONTACT TIPS: TO GET A 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 AND WITHOUT THE USE OF PUSH PULL GUNS.
Ed was working as the senior weld engineer for ABB Robotics Div. Fort Collins. CO.
USING THE BEST PULSED POWER SOURCE AVAILABLE (OTC) IN THE 1990s AND STILL THE BEST PULSED EQUIPMENT AVAILABLE IN 2008, ED COMPLETED THE 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 WELD EXPERTISE TO THE ROBOT PROGRAM.
The robot 's greatest weld challenge is
when you have robots working together
If one robot has a weld issue the other 3 go down
1990s: Fort Collins. CO. Four ABB robots in one cell working together on a complex, thin gage, aluminum golf cart frame. No push-pull guns and a customers requirement of minimum robot down time and minimum weld rework made this an interesting welding project. Each of the ABB robots was responsible for up to 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 was a challenge for 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, Alco Tech dee-reelers and hard plastic liners. Ed set weld data that compensated for the common aluminum gage part fit and gap issues and of course optimum start and stop data.
The aluminun robot line began production in early 1998. Since that time, the company has produced more than 50,000 aluminum golf cart frames. Two people operate the system one loads a fixture while the robots are welding in the other. Arc on time for the 130 welds on the cart frames is approx 6 minutes. When you add the load and unload parts time the total cycle time is 12 minutes as compared with 27 minutes to manually weld the frames.
This 10 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.
|
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.
| First
digit is principle aluminum alloy. First digit also describes the aluminum series.
Ksi is ultimate tensile strength range. | |||
|
> 99% Aluminum |
non heat treatable |
10-27 ksi |
|
Alu - Copper
approx. | heat treatable | 27-62 ksi |
|
Alu-Manganese. Provides incr eased strength | non heat treatable | 16-41 ksi |
|
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 |
|
Alu - Magnesium. Increases strength | none heat treatable | 18-51 ksi |
|
Alu Magnesium
and Silicon | heat treatable | 18 - 58 ksi |
|
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 |
The typical weld characteristics of steel or stainless don't apply when welding aluminum. Aluminum has higher thermal conductivity and lower melting temperatures, both factors will influence weld solidification, weld burn through potential and warpage problems.
None Heat Treatable 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 + MgFiller alloys used to join non-heat-treatable alloys typically come from three alloy groups:
1xxx
4xxx
5xxx
Commonly used filler alloys for none heat treatable alloys include,
1100, 1188,
4043, 4047,
5554, 5654, 5183, 5356, 5556.
When 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 however 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. 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 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.
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.
[] 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 non-magnetic 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.
[] 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 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 Porosity and Hydrogen. Aluminium 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 vapour from the 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 hot cracking is a result of high thermal stresses, weld shrinkage and metallurgical reactions while the aluminum weld metal solidifies.
ALUMINUM 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 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.
[e] 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 with 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 knowlege and a clean
weld surface and you wont produce weld 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 molecules, the fore hand (push) technique, mechanical cleaning, wire brushing, solvents and chemical etching are used for the oxide removal.
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 sensititivity 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.
Aluminum Welding
The reason why aluminum is specified for so many jobs is aluminum alloys can provide unique physical properties.
Weight. Aluminum is three times lighter than steel and yet aluminum can provide higher strength when alloyed with specific elements.
Conductivity. Aluminum can conduct electricity six times better than steel. The high electrical conductivity makes the effect of electrical wire stick-out in MIG welding less of a concern when compared to steel MIG welding.
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.
None Magnetic. Since its non-magnetic, arc blow is not a problem during aluminum welding.
Thermal Conductivity. With a thermal conductivity rate that is five times higher than steel and the aluminum welds
Aluminum alloys that are difficult to weld.
Alloys that may be sensitive to hot cracking are found in the 2xxx series, 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 dissimiler alum alloys as extending the coherance 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.Five Common Aluminum, MIG Filler Welding Metals:
5356 - 4043 - 1100 - 5556 - 4047Usually 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"?
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.
Weld Strength and Weld Heat Considerations:
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,
[2] excess preheating,
[3] slow weld speeds,
[4] weld weaves,
[5] oversized welds,
[6] multi-pass welds.
[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 transvers 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.
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 and 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). Ifluenced 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. Pease 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.
