Questions You Should Know about Aluminum Alloy Welding Wire

If you want to learn more, please visit our website.

Welding aluminum

Aluminum in its pure form is a relatively soft metal that has many uses, but which requires the addition of an alloy or alloys to increase its strength and to add other qualities suitable for different applications. Common alloys are: copper, magnesium, silicon, manganese and zinc. They are identified by their series numbers:

• Wrought Series Alloy groups
• 1xxx 99% minimum aluminum purity
• 2xxx copper
• 3xxx manganese
• 4xxx silicon
• 5xxx magnesium
• 6xxx magnesium-silicon
• 7xxx zinc
• 8xxx other
• 5xxx magnesium
• 6xxx magnesium-silicon
• 7xxx zinc
• 8xxx other

Aluminum, especially thin-gauge aluminum, presents some unique welding challenges. For many, GTAW is the preferred process, but GMAW offers some obvious benefits: higher deposition rates, less operator training and higher productivity. With these benefits come a few challenges, namely wire feeding and selecting the right type of filler metal and equipment. These challenges can be easily met, however, by knowing the answers to some common questions.

Frequently asked questions 

What is the best wire for welding aluminum?      

While filler metal for steel is typically chosen by matching the tensile strengths, strength is only one of the considerations when choosing an aluminum filler metal. Typically, there are several different aluminum filler metals that would be acceptable to use when welding aluminum base materials. In choosing a filler metal, consider:

-Base metal composition
-Ease of welding
-Joint design
-Dilution (when the filler wire and base metal combine in the weld puddle to create a different chemical make up in the weld)
-Strength of the weld
-Hot cracking sensitivity
-Ductility
-Corrosion in service
-Color matching, if the material is anodized
-Elevated service temperature (150-350 Fahrenheit)

Different filler metals address these considerations to varying degrees. In general, if strength is the primary consideration, the filler metal should closely match the base metal in tensile, yield and ductility.

Most consumable manufacturers, as well as the American Welding Society (AWS), offer information listing the relative values of these considerations of their filler metals for each base alloy. Always make sure to use an aluminum filler metal selection chart to address the weld properties listed above.

Are there any general-purpose aluminum welding wires?

Traditionally, welders have relied on AWS and wires, as they can be used with the most widely used aluminum alloy base metals. Hobart, however, offers an alternative to filler metals to increase strength and quality. The MaxalMig®  aluminum wire offers approximately 20% higher tensile strength and doesn&#;t rely on diluting the aluminum base material to gain strength. This feature often allows welders to make smaller, single-pass welds and still get reliable strength. It also helps minimize the risk of distortion since heat input is lower. 

Featured content:
10 Facts You Should Know about Electric Vehicles
T-Top fabrication Aluminum vs. Stainless
Top Benefits of Using ER70S-3 0mm Welding Wire Explained

Jinertai contains other products and information you need, so please check it out.

Are there any special storage considerations for aluminum filler metal wire?

Aluminum as a filler metal has the same oxidation problems as all aluminum. When left open, either on the shelf or installed on the welder, aluminum filler wire will oxidize, which can lead to an erratic arc. The oxidation adds resistance, can produce smut and can change the wire&#;s ability to feed smoothly. Many operators have spent a great deal of time adjusting tension settings, changing contact tips or checking the shielding gas trying to fix the problem when it was the oxidized wire that was at fault.

How do I eliminate &#;birdnesting&#; and other wire feeding problems?

Because of its low columnar strength, feeding aluminum wire has been likened to pushing a wet noodle through a straw. Birdnesting, or the tangling of the wire between the drive roll and the liner, is a common, time-consuming and costly problem. Clearing it requires the operator to stop welding, cut the wire, discard the wire in the gun and re-feed new wire through the liner. It also may require cleaning or changing the contact tip because of the burnback caused when the wire stops feeding.

There are several ways to feed aluminum wire: Push only, spool gun, push-pull system and continuous feed push-only system.

Push only: Feeding aluminum wire through a push-only system can be difficult, but it can be done on a limited basis. It requires u-groove drive rolls to provide more surface contact with the wire, adequate drive-roll pressure and the ability to keep the gun cable straight. Any resistance in the line will likely cause the wire to misfeed. Thicker wire, such as 1/16 inch, may be fed consistently in a push-feed system. But for thinner gauges, such as .030 inch, push feeding is not very dependable.

Spool gun: Welding aluminum with a spool gun, such as the Spoolmate&#; or Spoolmatic® series of guns, eliminates the possibility of birdnesting by putting a 4-inch (1-pound) spool on the gun, so the wire only feeds a few inches. Spool guns can accommodate aluminum wire diameters from .023 to 1/16 inch and allow the operator to use longer cables (15-50 foot).

A spool gun needs to have the roll changed after every pound of wire is used, compared with the 16- or 22-pound spool on a push-pull system. In tight spaces, the spool may limit access, requiring the operator to use a longer stickout. If the operator is using several pounds of aluminum per day, the few minutes needed to change spools can add up. Also, the chance of burnback exists when the end of a spool is reached, so many operators stop when a few turns are left on the spool.

Push-pull gun: With a push-pull gun, a motor in the gun pulls the wire through the liner, while the motor in the welder or feeder control becomes an assist motor. By maintaining consistent tension on the wire, the push-pull system helps eliminate birdnesting. It is more ergonomic than the spool gun since the weight of the spool is not in the operator&#;s hands.

Also, the spool needs to be changed less often than on a spool gun and allows the purchase of larger spools. A push-pull gun also allows cables up to 50 feet long. The only disadvantage to push-pull systems is their relatively higher price tag, but the increased productivity and the financial advantage of buying larger spools usually provide a quick return on investment. When you compare the cost of 16 1-pound spools of .035-inch aluminum filler wire with one 16-pound spool of the same diameter wire, plus the time to change 16 spools versus one spool, you&#;ll see that for high-volume use, a push-pull system makes financial sense. 

A welding distributor, picked at random, lists a price for a 1-pound spool of .035-inch aluminum wire as $11.46. A 16-pound roll lists for $170.24, which works out to a difference of $0.82 per pound. Now, add the time for 16 spool changes (and possibly burnbacks) for the spool gun as compared with one change for the larger spool. At five minutes to change a spool, that&#;s 80 minutes of extra time for each 16 pounds of filler wire used.

Continuous-feed push system: This is a relatively new addition to the field. This type of system uses a special drive system that maintains continuous contact with the wire and eliminates the possibility of birdnesting since there is no gap between the drive rolls and the liner. While it is limited to pushing the wire 15 feet, the gun is lighter than either the spool gun or the push-pull gun and requires no additional maintenance.

Check out this article for more MIG welding aluminum best practices.

Which transfer mode should I use when MIG welding aluminum?

The short-circuit transfer mode is not recommended for aluminum. It&#;s almost impossible to obtain good fusion and the weld will be prone to breaking or cracking. It should certainly not be used when appearance or strength is an issue.

In spray transfer, molten droplets are smoothly transferred from the electrode to the puddle. The arc is very smooth and stable and produces a nice appearance with good fusion at the sides. Since it involves high heat, burn-through can be an issue on thin (1/8 inch or less) material, so it requires a faster travel speed and a thin-gauge (.030-inch) filler wire to keep the heat input down.

With pulsed welding, or pulsed MIG, you&#;re always in spray transfer mode; the wire will transfer across the arc, then drop to a lower amperage, allowing the puddle to cool while maintaining the arc. This allows for out-of-position welding, and the pulse agitates the weld puddle, aiding the cleaning action. Because the heat input can be better controlled, (on some machines, you can even shape the pulse waves) you can weld thinner-gauge material and use a larger-diameter wire (up to 3/64 inch), with a decreased chance of burn-through and increased deposition rates.

Because you can use 3/64-inch filler wire to weld thin-gauge material, you not only increase the deposition rate and aid feeding by using a stiffer wire, you can save money on filler wire. The same distributor who charges $170.24 for a 16-pound      spool of .035-inch aluminum filler wire (see above), charges $200.20 for a 22-pound      spool of 3/64-inch wire &#; a difference of $0.63 per pound. Add in the decreased time and materials for rejected parts, and pulsed MIG may look like an attractive alternative, depending on your particular application.      
 
Pulsed MIG is simple to use and a very easy process to train operators to make quality welds with &#; much easier than it is to train a TIG operator. Plus, the appearance of a pulsed MIG weld can rival that of a TIG weld.    

I think Lawrence is on to something with his comments...

On another not, I found this article while reading some of the articles in the archive for the Fabricator:

http://www.thefabricator.com/article/aluminumwelding/succeed-at-welding-thick-aluminum-with-the-right-material-preparation-filler-choice-and-equipment

And as I was reading this, a couple of things jumped out at me regarding your situation...

Question: What are some equipment considerations?

Hoes: Water-cooled GTAW [gas tungsten arc welding] torches and GMAW [gas metal arc welding] guns should be considered for production welding of aluminum when amperage exceeds 150. Lighter air-cooled GTAW torches, GMAW spool guns, and push-pull systems sometimes will work for intermittent welding in this range, but will overheat when working at the higher amperage and duty cycles needed for production work.

Question: How do you prepare base materials and filler materials?

Burns: Materials need to be free of oil, grease, and moisture. Edges need to be more rounded than on thin materials to prevent premature melting, which causes lack of fusion (LOF) and lack of penetration (LOP). Often extended lands are used to get good fusion at the root, and the groove may be formed into a U shape.

Filler metals typically are from 3&#;32 (it should be 3/64" or at least 1/16th" diameter) to 3&#;16 in. These require special equipment and handling because of the springiness of the wire. When using large-diameter wire, note the duty cycle and be aware that most welding equipment such as torches and power supplies are rated using CO2, not argon or argon/helium mixes, which increase the heat to the gun and lower the duty cycle.

My question is:"If you are working from a WPS, is the filler metal dia. an essential variable in let's say AWS D1.2?" if not, then why not change to a thicker diameter and a more robust GMAW gun along with using an argon/helium mix (Is this a nonessential variable too?) so you don't need to increase the current and you control your HAZ better as well as the weld cooling down slower? i ask this because currently I'm not familiar with AWS D1.2.

Hoes: Oxide removal is also critical. As aluminum is stored, the oxide layer thickens, absorbs hydrogen, and traps impurities that can be absorbed into the weld puddle. Hydrogen, readily absorbed into liquid aluminum weld metal, turns to porosity when the weld solidifies.

Remove oxide with a clean stainless steel brush. Be careful not to use too much pressure if using a power tool. A power brush can dig into the aluminum, roll it over, and burnish it, trapping contaminants under the surface. Use grinding wheels and sanding discs that are designed for aluminum to minimize contamination. Machining instead of grinding can result in a cleaner surface, but remove all coolants or lubricants before welding. Paint and coatings also need to be removed from the weld area. Before brushing, clean and degrease with acetone, nonchlorinated brake cleaners, or citrus degreasers to avoid spreading contaminants. There are stronger cleaning solvents on the market, but exercise caution to use them safely.

Aluminum welding consumables should be properly stored to avoid shop dirt contamination and excessive oxide formation. This is especially important with GMAW consumables because the insulating oxide layer can cause problems with electrical contact between the aluminum electrode and the copper contact tip. Also, a large amount of surface area on small-diameter wires forces more contaminants into the weld deposit. GTAW cut-to-length consumables can be cleaned, but it is impossible with GMAW wire.

Question: What causes cracking? What prevents it?

Burns: Two things cause hot, or solidification, cracking. The first is stress-related. When the filler material solidifies at a temperature equal to or below that of the base material, stress caused by the metal shrinkage pulls on the molten pool or weld metal and causes cracking. The second is more of a chemistry issue. Alloys such as the 6XXX series that have a wide liquidus/solidus temperature range are more prone to cracking. The temperature difference creates a mushy range during solidification, forming coherent interlocking dendrites that result in voids between the grains. As the coherence range widens, it becomes more prone to what might resemble microcracking in the weld.

Stress corrosion cracking (SCC) is basically a chemistry issue in which some alloy elements, often accelerated by heat, have a galvanic reaction to each other. This is called metallurgical susceptibility. Environmental atmosphere and temperature contribute to this reaction that can lead to failure when stress is added.

Hoes: When the amperage is turned off quickly at the end of a weld, the puddle solidifies quickly and leaves a concave crater that pulls apart and cracks when it shrinks. Some advanced GMAW machines have crater-fill features with which the machine continues to weld at a reduced current for a period of time after releasing the trigger. This fills the crater and ends the weld with a convex bead, which is not prone to cracking. When using equipment without a crater-fill feature, double-back at the end of the weld to leave the crater on the weld. With manual GTAW, backing off the current with the foot pedal and adding a little extra filler metal at the end of the weld can also fill the crater.

TIG welds often have a tendency to crack if there is not enough filler metal, especially when working with crack-sensitive alloys like the 6XXX series. Dilute enough filler metal into the puddle to change the weld chemistry. Starving the puddle by not adding enough filler metal often leads to cracks. 6XXX alloys never should be autogenously welded (without filler). The silicon-alloyed 4XXX filler metal is less crack-sensitive than the commonly used 5XXX alloys but should not be used on alloys that contain more than 21&#;2 percent magnesium. The commonly used alloy is one of the only ones in the magnesium-alloyed family that can be welded with the 4XXX filler metals.

Question: What visible signs indicate a good weld? A bad weld?

Burns: Sometimes a good-looking weld is not a good weld. Unfortunately, the best way to evaluate a weld is to cut it apart, look at the depth of penetration, fusion, and porosity level. While we can&#;t use this method without destroying every weld, using known welding codes, such as those published by CWB and AWS, and following qualifying procedures increase the probability of achieving quality results.

Hoes: Look at bead shape. A good weld will be flat to slightly convex, without concave shapes or hollows between the ripples or in the crater, and have good wash-in at the toes. Check carefully for cracks using dye-penetrant inspection. If welds are ropey or convex, it is usually an indication that not enough energy was provided to the weld and cold procedures or undersized equipment was used. This is often an indication of possible LOF (Lack Of Fusion).

Question: How can a welder minimize the heat-affected zone (HAZ)?

Burns: Larger wire, fast travel speeds, and fewer passes all reduce the HAZ.
Hoes: High currents and helium additions to the shielding gas add energy when welding to increase travel speed, which reduces the HAZ. Use stringers, no weaving.

Question: How does shielding gas affect the thick weld?

Burns: In thick aluminum welding, helium is often added to argon to increase heat input. This can flatten the weld bead, increase root width penetration, and reduce porosity.

Hoes: Helium/argon gas mixtures, often utilized when GTAW on material over 1&#;4 in. thick and GMAW on material over 1&#;2 in. thick, transfers more heat to the weld than argon, which aids in welding thicker sections of aluminum. The broader bead profile resulting from the helium addition is not as deep in the middle, but it solidifies slower and allows some of the hydrogen to escape, reducing porosity.

Be sure there are no drafts or breezes removing gas from the weld area, leaks in the system, loose fittings, or spatter buildup in the nozzle. Check the purity of the gas. Contaminated gas really shows up with aluminum welding. Low-pressure tanks, below 500 lbs., can cause problems. Change them.

Question: How can a welder avoid wire feed problems?

Burns: Welding thick material with large-diameter wire can cause overheating of the contact tip if the weld gun or torch is not sufficiently cooled. The result could be loss of contact to the wire as well as excessive buildup at the exit of the contact tip. Use the proper equipment.

Hoes: Larger wire is going to feed easier than smaller wire when pushing. Use aluminum contact tips that are slightly oversized to accommodate the expansion of the aluminum wire as it heats up. Be sure the guide tube is plastic and the U-groove drive rolls are polished to prevent wire damage. The brake should be loose enough for the roll to spin freely without dumping wire when welding stops. Drive roll tension should be set back compared to what is used for steel.

Question: What extra steps should be taken to provide a safe environment?

Burns: Recognize that current must increase substantially to perform thick welds. With this increase in amperage, the heat and light given off as byproducts can result in burns from both temperature and ultraviolet light. Sufficient protection should be in place for both.

Hoes: Extra precautions should be taken to protect your eyes and skin and surrounding personnel. ANSI-approved safety glasses with side shields should be worn by surrounding personnel and as secondary protection from UV light under your hood. Higher levels of ozone result from thick aluminum welding conditions and enter your breathing zone. Adequate ventilation should be used to keep fume levels in conformance with OSHA standards while using caution not to exhaust shielding gas from the weld. Reference ANSI Z49.1.

The entire article really jumped out at me because it was fundamentally sound and logical... The basics... So take it and see if anything jumps out at you jsdwelder.

Here's the link:

http://www.thefabricator.com/article/aluminumwelding/succeed-at-welding-thick-aluminum-with-the-right-material-preparation-filler-choice-and-equipment

Here's another good article that can be used also to help your situation:

Aluminum welding Q&A: About soot, porosity, and equipment:

http://www.thefabricator.com/article/aluminumwelding/aluminum-welding-qa-about-soot-porosity-and-equipment

This one jumped out at me:

Q: My company fabricates a variety of aluminum products, and sometimes we find porosity in the welds after cutting and etching. We have checked our argon gas shielding carefully and find it adequate. We have also consulted the aluminum material suppliers, both raw plate and sheet and filler wire. They all have recommended cleaning processes, which we now employ. However, we continue to find porosity in our welds periodically. Is it possible the GMAW power source is influencing this contamination?

A: Unless the arc your present welding equipment generates is extremely erratic, you probably do not have a machine problem. Electricity generated in the arc is not contaminated. However, there is a type of pulse GMAW transfer available in some new generations of GMAW machines that can help eliminate this problem. This process superimposes a low-frequency pulse in combination with the normal high-speed pulse frequency. Certain low frequencies actually agitate the molten weld puddle at a rate that allows typically trapped gases or impurities to escape.

This low-frequency process offers several additional advantages. Low-frequency weld puddle agitation has been found to reduce grain growth in aluminum materials, which minimizes weld cracking susceptibility. The most obvious benefit is the weld surface appearance. The lower frequency provides a weld bead that looks very similar to GTAW welding but at the speed of the GMAW process.

Check with power source manufacturers to find out which offer this process. Ask suppliers for data to confirm a reduction or elimination of porosity and reduction of crack susceptibility. Also request a demonstration to see if the machine provides the GTAW-like bead appearance.

An oldie but a goodie: How to recognize, minimize weld smut:

http://www.thefabricator.com/article/aluminumwelding/how-to-recognize-minimize-weld-smut

Here's another one:

Tackling aluminum GMAW - Technology advancements in power sources simplify aluminum welding:

http://www.thefabricator.com/article/aluminumwelding/tackling-aluminum-gmaw

And this one which can be important in your case:  Age before welding in T6:

Frank Armao discusses why weld strength increases when incorporating an aging cycle prior to welding in the T6 temper...

http://www.thefabricator.com/article/aluminumwelding/age-before-welding-in-t6

Which filler wire is best for welding -T6 aluminum, or ?:

http://www.thefabricator.com/article/aluminumwelding/which-filler-wire-is-best-for-welding--t6-aluminum--or-r

And this: Achieving T6 designation for :

http://www.thefabricator.com/article/aluminumwelding/achieving-t6-designation-for-

Let's not forget this either: Preparing, testing bend samples:

http://www.thefabricator.com/author/frank-armao?page=2

Here's a little reference article covering aluminium H and T temper designations:

http://www.thefabricator.com/article/aluminumwelding/welding-aluminum

Now, if all of these factors have been covered and you still have issues then I wish you good luck in solving your problem.

Respectfully,
Henry

I think Lawrence is on to something with his comments...On another not, I found this article while reading some of the articles in the archive for the Fabricator:And as I was reading this, a couple of things jumped out at me regarding your situation...Water-cooled GTAW [gas tungsten arc welding] torches and GMAW [gas metal arc welding] guns should be considered for production welding of aluminum when amperage exceeds 150. Lighter air-cooled GTAW torches, GMAW spool guns, and push-pull systems sometimes will work for intermittent welding in this range, but will overheat when working at the higher amperage and duty cycles needed for production work.Materials need to be free of oil, grease, and moisture. Edges need to be more rounded than on thin materials to prevent premature melting, which causes lack of fusion (LOF) and lack of penetration (LOP). Often extended lands are used to get good fusion at the root, and the groove may be formed into a U shape.Filler metals typically are from 3&#;32 (it should be 3/64" or at least 1/16th" diameter) to 3&#;16 in. These require special equipment and handling because of the springiness of the wire. When using large-diameter wire, note the duty cycle and be aware that most welding equipment such as torches and power supplies are rated using CO2, not argon or argon/helium mixes, which increase the heat to the gun and lower the duty cycle.Oxide removal is also critical. As aluminum is stored, the oxide layer thickens, absorbs hydrogen, and traps impurities that can be absorbed into the weld puddle. Hydrogen, readily absorbed into liquid aluminum weld metal, turns to porosity when the weld solidifies.Remove oxide with a clean stainless steel brush. Be careful not to use too much pressure if using a power tool. A power brush can dig into the aluminum, roll it over, and burnish it, trapping contaminants under the surface. Use grinding wheels and sanding discs that are designed for aluminum to minimize contamination. Machining instead of grinding can result in a cleaner surface, but remove all coolants or lubricants before welding. Paint and coatings also need to be removed from the weld area. Before brushing, clean and degrease with acetone, nonchlorinated brake cleaners, or citrus degreasers to avoid spreading contaminants. There are stronger cleaning solvents on the market, but exercise caution to use them safely.Aluminum welding consumables should be properly stored to avoid shop dirt contamination and excessive oxide formation. This is especially important with GMAW consumables because the insulating oxide layer can cause problems with electrical contact between the aluminum electrode and the copper contact tip.Two things cause hot, or solidification, cracking. The first is stress-related. When the filler material solidifies at a temperature equal to or below that of the base material, stress caused by the metal shrinkage pulls on the molten pool or weld metal and causes cracking. The second is more of a chemistry issue. Alloys such as the 6XXX series that have a wide liquidus/solidus temperature range are more prone to cracking. The temperature difference creates a mushy range during solidification, forming coherent interlocking dendrites that result in voids between the grains. As the coherence range widens, it becomes more prone to what might resemble microcracking in the weld.Stress corrosion cracking (SCC) is basically a chemistry issue in which some alloy elements, often accelerated by heat, have a galvanic reaction to each other. This is called metallurgical susceptibility. Environmental atmosphere and temperature contribute to this reaction that can lead to failure when stress is added.When the amperage is turned off quickly at the end of a weld, the puddle solidifies quickly and leaves a concave crater that pulls apart and cracks when it shrinks. Some advanced GMAW machines have crater-fill features with which the machine continues to weld at a reduced current for a period of time after releasing the trigger. This fills the crater and ends the weld with a convex bead, which is not prone to cracking. When using equipment without a crater-fill feature, double-back at the end of the weld to leave the crater on the weld. With manual GTAW, backing off the current with the foot pedal and adding a little extra filler metal at the end of the weld can also fill the crater.TIG welds often have a tendency to crack if there is not enough filler metal, especially when working with crack-sensitive alloys like the 6XXX series. Dilute enough filler metal into the puddle to change the weld chemistry. Starving the puddle by not adding enough filler metal often leads to cracks. 6XXX alloys never should be autogenously welded (without filler). The silicon-alloyed 4XXX filler metal is less crack-sensitive than the commonly used 5XXX alloys but should not be used on alloys that contain more than 21&#;2 percent magnesium. The commonly used alloy is one of the only ones in the magnesium-alloyed family that can be welded with the 4XXX filler metals.Sometimes a good-looking weld is not a good weld. Unfortunately, the best way to evaluate a weld is to cut it apart, look at the depth of penetration, fusion, and porosity level. While we can&#;t use this method without destroying every weld, using known welding codes, such as those published by CWB and AWS, and following qualifying procedures increase the probability of achieving quality results.Look at bead shape. A good weld will be flat to slightly convex, without concave shapes or hollows between the ripples or in the crater, and have good wash-in at the toes. Check carefully for cracks using dye-penetrant inspection. If welds are ropey or convex, it is usually an indication that not enough energy was provided to the weld and cold procedures or undersized equipment was used. This is often an indication of possible LOF (Lack Of Fusion).Larger wire, fast travel speeds, and fewer passes all reduce the HAZ.In thick aluminum welding, helium is often added to argon to increase heat input. This can flatten the weld bead, increase root width penetration, and reduce porosity.Helium/argon gas mixtures, often utilized when GTAW on material over 1&#;4 in. thick and GMAW on material over 1&#;2 in. thick, transfers more heat to the weld than argon, which aids in welding thicker sections of aluminum. The broader bead profile resulting from the helium addition is not as deep in the middle, but it solidifies slower and allows some of the hydrogen to escape, reducing porosity.Be sure there are no drafts or breezes removing gas from the weld area, leaks in the system, loose fittings, or spatter buildup in the nozzle. Check the purity of the gas. Contaminated gas really shows up with aluminum welding. Low-pressure tanks, below 500 lbs., can cause problems. Change them.Welding thick material with large-diameter wire can cause overheating of the contact tip if the weld gun or torch is not sufficiently cooled. The result could be loss of contact to the wire as well as excessive buildup at the exit of the contact tip. Use the proper equipment.Larger wire is going to feed easier than smaller wire when pushing. Use aluminum contact tips that are slightly oversized to accommodate the expansion of the aluminum wire as it heats up. Be sure the guide tube is plastic and the U-groove drive rolls are polished to prevent wire damage. The brake should be loose enough for the roll to spin freely without dumping wire when welding stops. Drive roll tension should be set back compared to what is used for steel.Recognize that current must increase substantially to perform thick welds. With this increase in amperage, the heat and light given off as byproducts can result in burns from both temperature and ultraviolet light. Sufficient protection should be in place for both.Extra precautions should be taken to protect your eyes and skin and surrounding personnel. ANSI-approved safety glasses with side shields should be worn by surrounding personnel and as secondary protection from UV light under your hood. Higher levels of ozone result from thick aluminum welding conditions and enter your breathing zone. Adequate ventilation should be used to keep fume levels in conformance with OSHA standards while using caution not to exhaust shielding gas from the weld. Reference ANSI Z49.1.The entire article really jumped out at me because it was fundamentally sound and logical... The basics... So take it and see if anything jumps out at you jsdwelder.Here's the link:Here's another good article that can be used also to help your situation:Aluminum welding Q&A: About soot, porosity, and equipment:This one jumped out at me:Unless the arc your present welding equipment generates is extremely erratic, you probably do not have a machine problem. Electricity generated in the arc is not contaminated. However, there is a type of pulse GMAW transfer available in some new generations of GMAW machines that can help eliminate this problem. This process superimposes a low-frequency pulse in combination with the normal high-speed pulse frequency. Certain low frequencies actually agitate the molten weld puddle at a rate that allows typically trapped gases or impurities to escape.This low-frequency process offers several additional advantages. Low-frequency weld puddle agitation has been found to reduce grain growth in aluminum materials, which minimizes weld cracking susceptibility. The most obvious benefit is the weld surface appearance. The lower frequency provides a weld bead that looks very similar to GTAW welding but at the speed of the GMAW process.Check with power source manufacturers to find out which offer this process. Ask suppliers for data to confirm a reduction or elimination of porosity and reduction of crack susceptibility. Also request a demonstration to see if the machine provides the GTAW-like bead appearance.An oldie but a goodie: How to recognize, minimize weld smut:Here's another one:Tackling aluminum GMAW - Technology advancements in power sources simplify aluminum welding:And this one which can be important in your case: Age before welding in T6:Frank Armao discusses why weld strength increases when incorporating an aging cycle prior to welding in the T6 temper...Which filler wire is best for welding -T6 aluminum, or ?:And this: Achieving T6 designation for :Let's not forget this either: Preparing, testing bend samples:Here's a little reference article covering aluminium H and T temper designations:Now, if all of these factors have been covered and you still have issues then I wish you good luck in solving your problem.Respectfully,Henry

If you are looking for more details, kindly visit Aluminum Alloy Welding Wire.