Cleaning aluminum for welding

[damae]

Does preheating aluminum with a propane torch contaminate the cleaned aluminum surfaces? I'm told that for TIG welding, cleaning is VERY important. Should I be cleaning the aluminum again after it is preheated? I have been using an angle grinder with stainless wire wheel to remove the annodized coating on my practice aluminum extrusions.

I'm starting to make decent looking lap-joint welds on clean 1/8" aluminum extrusion. (I'm also very good at coating tungsten with aluminum!)

I'm new to TIG welding and have practiced for a total of just a few hours. Recently, I attempted to butt weld two 1/2" thick aluminum plates of unknown aluminum grade (perhaps 6061?). I knew the thickness would be a problem, so I cleaned very carefully and preheated the pieces with a propane torch. Then I cranked the amperage up and proceeded to make a mess of the weld. The weld ended up very drossy and dull. It was hard to break the surface tension of the molten aluminum sitting on top of the butt weld, which is the way it acted when I was trying to weld dirty (not cleaned) aluminum.

Any ideas as to my problem? Could be that I'm welding on a 6xxx series aluminum with 4xxx wire? Or does the propane flame cause some contamination of the weld surfaces?

[thkoutsidthebox]

One possibility is that if you brush too hard with the stainless wire brush you can drive the oxidized surface particles into the metal, and when you begin to weld they are still there waiting to cause problems. This might be a possibility because of using the brush on the grinder. Maybe try manually brushing the surface instead. The wire AFIK does have to be appropriate to your type of aluminium plate. Take this with a pinch of salt as I have limited experience. The question about the propane flame is very interesting. Unfortunately I can't offer an answer but am looking forward to seeing what others say.

[ezg55]

When TIG welding aluminum it if best to clean using IPA to insure that all oils, paint, etc are removed. Mechanical cleaning is only needed when the aluminum has been anodized. Grind the weld area using a grinding wheel made for aluminum. You can find this grinding wheel at your welding supply store. It is dangerous to use a grinding wheel designed for carbon steel on aluminum because the aluminum can build up on the wheel and overheat causing it to shatter. Pre-heating thick aluminum plate is ok since it will remove any residual moisture and make it easier to weld. Do not exceed 600 degrees Fahrenheit or quench the aluminum while hot since this will anneal the metal and make it soft.
Avoid contamination of the weld area by not removing the TIG torch shielding gas or the filler rod from the weld area for a few seconds after you stop the weld. Also during the welding process try to keep the filler rod close to the TIG cup to prevent the filler rod from being exposed to air which will oxidize it. As you move the rod back into the weld puddle you will cause contamination of the weld area. A good TIG welder can lay a bead, with a 36 inch filler rod, feeding with one hand without stopping with perfect weld width and height. Keep up the practice.

[ViperTX]

Also....only use the stainless steel brush on Aluminum....and brush in only one direction....

your welding supply store will tell which wire to use....it all depends on whether you're to anodize or plate the aluminum afterwards...

[damae]

Thanks to all for the great comments so far! TIG is very exciting and I'm committed to learning how to do it!

Originally Posted by ezg55 ...Mechanical cleaning is only needed when the aluminum has been anodized....

On the extruded aluminum, I was using the stainless wire wheel to strip the annodization. I thought that brushing is also needed to remove oxidation, even if the aluminum is not annodized and appears clean. Will the alcohol remove the oxidation too? Or is removing the oxidation not as neccessary as I thought it was?

Thanks for the tip not to exceed 600F -- I think it was well below that temperature, but next time I'll use an infrared thermometer to verify. Also a good reminder to keep the filler rod in the argon stream -- which I did not do. I'll try again following these tips!

Originally Posted by ezg55 ... A good TIG welder can lay a bead, with a 36 inch filler rod, feeding with one hand without stopping with perfect weld width and height. Keep up the practice.

Feeding the whole 36 inch rod in one go? That's impressive. I tried to do this, but my feed hand keeps ending up 1" from the weld and so I have to stop. I'm still a bit awkward trying to walk my hand back along the filler rod without stopping. When I try it, I foul the tungsten with the filler rod as it bounces around.

One technique that worked was backing off the foot pedal, just barely maintaining the arc until the weld cools with the filler rod still in the puddle. When the puddle gets solid enough (about 2 seconds), I can move my hand back another 10" easily because the business end of the filler rod is stuck in the puddle and won't bounce around. Since the arc is still going, I just ease back onto the pedal and the aluminum pools again instantly. Anyone else do this? I have a feeling it's a bad habbit, but don't know better yet. =)

Originally Posted by ViperTX Also....only use the stainless steel brush on Aluminum....and brush in only one direction....your welding supply store will tell which wire to use....it all depends on whether you're to anodize or plate the aluminum afterwards...

Another good point. I use Quimby welding supply in Portland; they are very knowledgeable and were poised to suggest the perfect filler rod for my base metal.... if only I knew what it the base metal was.

Originally Posted by thkoutsidthebox One possibility is that if you brush too hard with the stainless wire brush you can drive the oxidized surface particles into the metal, and when you begin to weld they are still there waiting to cause problems.....

I'll order a stainless handheld brush and try it.

Originally Posted by thkoutsidthebox The question about the propane flame is very interesting. Unfortunately I can't offer an answer but am looking forward to seeing what others say.

Yes, I would love to hear if anyone has had success TIGing aluminum after preheating with a flame! I plan to do a lot of aluminum, so this will be a handy thing to know.

[thkoutsidthebox]

Originally Posted by damae Will the alcohol remove the oxidation too? Or is removing the oxidation not as neccessary as I thought it was?

Using solvents by themselves is a recognised alternative method to prep aluminium. Just ensure its the correct solvents. Some more experienced people Im sure can elaborate on this.

[damae]

Originally Posted by thkoutsidthebox Using solvents by themselves is a recognised alternative method to prep aluminium. Just ensure its the correct solvents. Some more experienced people Im sure can elaborate on this.

Thanks for the tip, I didn't know it could be done with solvents alone. I'll ask my welding supply store next time I place an order.

[damae]

According to the experts at Quimby Welding Supply, my local supplier, preheating with any kind of flame will contaminate the weld seriously enough that it will need cleaning after applying the flame.

They recommend only applying a clean heat source such as an electric heating blanket (the welding specific kind, not the bedroom kind). An electric stove element will also work, but tranfering preheated pieces of aluminum from the kitchen to the garage might be tricky!

I'll try again without preheating and see if I have better results.

[mxtras]

You will likely see extremely limited benefit from your preheating efforts unless the material is wet. While it is necessary to preheat many of the more uncommon, high strength Aluminums prior to and during welding, with the more common extruded, structural alloys (6061, 6063) it is not required. Heating it to just 150 or 200 will drive out the moisture which is the only real benefit you will realize with preheating those alloys. In other words - don't worry about the preheat - you are wasting your effort in my opinion.

Look into "Alumi-brite" - it is a phosphoric acid cleaning solution for weld prep. I only use it occaisionally for heavily oxididized materials. It works really well on copper, by the way. 99% of the time, I simply put a fresh bevel on the edges and weld and I weld a lot of Aluminum extrusions.

To help keep you filler rod still, try resting it in the joint - just ahead of the arc where it won't melt but still in the shield. When the base is ready, advance it into the puddle then back it off just a bit but leave it in contact with the work - this will help you keep it steady. You can get a rythym going and make a nice, even bead. Play with the torch 'attack' angle and the filler rod angle to find a comfortable system for how you like to advance. You are pushing, right?

ER4043 is the filler for 6061 and 6063. You are in for a rude awakening if you are planning to anodize, though. The weld anodizes so-so, the parent metal anodizes ok but the HAZ does not anodize hardly at all (6061 and 6063 don't anodize all that great to begin with). 5053 is a different story and if you are planning to anodize, you might want to use this "architectural" alloy with the appropriate filler.

Scott

[thkoutsidthebox]

The following is quoted from the Lincoln electric site. It covers pretty much everything we've mentioned above:

A Guide to Aluminum Welding
Reprinted courtesy of Welding Design and Fabrication magazine.
Equipment Selection, Material Prep, Welding Technique...
A Guide to Aluminum Welding
Reprinted courtesy of Welding Design and Fabrication magazine.

Follow the rules of thumb offered here for selecting welding equipment, preparing base materials, applying proper technique, and visually inspecting weldments to ensure high-quality gas-metal-and gas tungsten-arc welds on aluminum alloys.
Even for those experienced in welding steels, welding aluminum alloys can present quite a challenge. Higher thermal conductivity and low melting point of aluminum alloys can easily lead to burnthrough unless welders follow prescribed procedures. Also, feeding aluminum welding wire during gas-metal-arc-welding (GMAW) presents a challenge because the wire is softer than steel, has a lower column strength, and tends to tangle at the drive roll.

To overcome these challenges, operators need to follow the rules of thumb and equipment-selection guidelines offered here...

Gas-metal-arc-welding:
Base-metal preparation: To weld aluminum, operators must take care to clean the base material and remove any aluminum oxide and hydrocarbon contamination from oils or cutting solvents. Aluminum oxide on the surface of the material melts at 3,700 F while the base-material aluminum underneath will melt at 1,200 F. Therefore, leaving any oxide on the surface of the base material will inhibit penetration of the filler metal into the workpiece.
To remove aluminum oxides, use a stainless-steel bristle wire brush or solvents and etching solutions. When using a stainless-steel brush, brush only in one direction. Take care to not brush too roughly: rough brushing can further imbed the oxides in the work piece. Also, use the brush only on aluminum work-don't clean aluminum with a brush that's been used on stainless or carbon steel. When using chemical etching solutions, make sure to remove them from the work before welding.
To minimize the risk of hydrocarbons from oils or cutting solvents entering the weld, remove them with a degreaser. Check that the degreaser does not contain any hydrocarbons.

Preheating: Preheating the aluminum workpiece can help avoid weld cracking. Preheating temperature should not exceed 230 F-use a temperature indicator to prevent overheating. In addition, placing tack welds at the beginning and end of the area to be welded will aid in the preheating effort. Welders should also preheat a thick piece of aluminum when welding it to a thin piece; if cold lapping occurs, try using run-on and run-off tabs.

The push technique: With aluminum, pushing the gun away from the weld puddle rather than pulling it will result in better cleaning action, reduced weld contamination, and improved shielding-gas coverage.

Travel speed: Aluminum welding needs to be performed "hot and fast." Unlike steel, the high thermal conductivity of aluminum dictates use of hotter amperage and voltage settings and higher weld-travel speeds. If travel speed is too slow, the welder risks excessive burnthrough, particularly on thin-gage aluminum sheet.

Shielding Gas: Argon, due to its good cleaning action and penetration profile, is the most common shielding gas used when welding aluminum. Welding 5XXX-series aluminum alloys, a shielding-gas mixture combining argon with helium - 75 percent helium maximum - will minimize the formation of magnesium oxide.

Welding wire: Select an aluminum filler wire that has a melting temperature similar to the base material. The more the operator can narrow-down the melting range of the metal, the easier it will be to weld the alloy. Obtain wire that is 3/64- or 1/16- inch diameter. The larger the wire diameter, the easier it feeds. To weld thin-gage material, an 0.035-inch diameter wire combined with a pulsed-welding procedure at a low wire-feed speed - 100 to 300 in./min - works well.

Convex-shaped welds: In aluminum welding, crater cracking causes most failures. Cracking results from the high rate of thermal expansion of aluminum and the considerable contractions that occur as welds cool. The risk of cracking is greatest with concave craters, since the surface of the crater contracts and tears as it cools. Therefore, welders should build-up craters to form a convex or mound shape. As the weld cools, the convex shape of the crater will compensate for contraction forces.

Power-source selection: When selecting a power source for GMAW of aluminum, first consider the method of transfer -spray-arc or pulse.
Constant-current (cc) and constant-voltage (cv) machines can be used for spray-arc welding. Spray-arc takes a tiny stream of molten metal and sprays it across the arc from the electrode wire to the base material. For thick aluminum that requires welding current in excess of 350 A, cc produces optimum results.
Pulse transfer is usually performed with an inverter power supply. Newer power supplies contain built-in pulsing procedures based on and filler-wire type and diameter. During pulsed GMAW, a droplet of filler metal transfers from the electrode to the workpiece during each pulse of current. This process produces positive droplet transfer and results in less spatter and faster follow speeds than does spray-transfer welding. Using the pulsed GMAW process on aluminum also better-controls heat input, easing out-of-position welding and allowing the operator to weld on thin-gage material at low wire-feed speeds and currents.

Wire feeder: The preferred method for feeding soft aluminum wire long distances is the push-pull method, which employs an enclosed wire-feed cabinet to protect the wire from the environment. A constant-torque variable-speed motor in the wire-feed cabinet helps push and guide the wire through the gun at a constant force and speed. A high-torque motor in the welding gun pulls the wire through and keeps wire-feed speed and arc length consistent.
In some shops, welders use the same wire feeders to deliver steel and aluminum wire. In this case, the use of plastic or Teflon liners will help ensure smooth, consistent aluminum-wire feeding. For guide tubes, use chisel-type outgoing and plastic incoming tubes to support the wire as close to the drive rolls as possible to prevent the wire from tangling. When welding, keep the gun cable as straight as possible to minimize wire-feed resistance. Check for proper alignment between drive rolls and guide tubes to prevent aluminum shaving.
Use drive rolls designed for aluminum. Set drive-roll tension to deliver an even wire-feed rate. Excessive tension will deform the wire and cause rough and erratic feeding; too-little tension results in uneven feeding. Both conditions can lead to an unstable arc and weld porosity.

Welding guns: Use a separate gun liner for welding aluminum. To prevent wire chaffing, try to restrain both ends of the liner to eliminate gaps between the liner and the gas diffuser on the gun.
Change liners often to minimize the potential for the abrasive aluminum oxide to cause wire-feeding problems.
Use a contact tip approximately 0.015 inch larger than the diameter of the filler metal being used - as the tip heats, it will expand into an oval shape and possibly restrict wire feeding. Generally, when a welding current exceeds 200 A use a water-cooled gun to minimize heat buildup and reduce wire-feeding difficulties.

[zcases]

Using 5356 filler will allow you to anodize 6061..........

[damae]

Scott, thanks for the tips on preheating, Alumi-brite, pushing technique and annodizing! I hadn't planned to annodize any of my work yet at least not until I get beyond practicing and my welds start to look good. I am starting to see the great importance of selecting the right filler rod. Yes, I'm using the push technique, but badly.

Thkoutsidethebox, thanks for your tips also. I read through the equivalent Miller guide on aluminum welding, but reading it in more than one place helps. The guide you posted seems to be for MIG, but I imagine the section on cleaning and preheating applies to TIG as well.

Zcases, thanks for the filler rod suggestion. I'll refer back to this thread when the time for annodizing comes.

Thanks to all for your generous help!