Question: I am using a 115V MIG welder. I have had great success using it to weld steel up to 0.25-in. thick, and want to try it on 6061 0.188-in. thick aluminum. I purchased the aluminum welding kit, installed it correctly, set the polarity to DC+ for MIG, used 100% argon gas, cleaned the surface of the aluminum with a new Scotchbrite pad, and set the feed and voltage per the owner's manual. I am also using the highest voltage and wire-feed speed listed in the manual. With everything set correctly, and a gas flow rate of 20 - 30 standard cubic feet per hour (SCFH), I still get no penetration, and the wire just balls-up at the tip and falls off in a glob on the aluminum surface. What am I doing wrong?
Answer: Your welder does not have enough power to weld aluminum this thick. Your instruction manual probably lists a maximum aluminum thickness of 0.105-in. (10 ga). You need more power to weld aluminum than steel because of aluminum's high thermal conductivity.

If you must weld the 0.188-in. thick aluminum and can't afford a bigger power supply, preheat the entire aluminum part to 300° F using a propane torch, kitchen oven, or whatever else is available and appropriate. Preheating aluminum is typically considered a last resort to solve lack-of-penetration because overheating softens the aluminum.

Do not to use Scotchbrite for pre-weld cleaning of aluminum. It deposits a residue that causes a lot of porosity in the weld. Instead, wipe the parts with a degreasing solvent such as acetone or paint thinner. Allow the solvent to evaporate, then remove any heavy aluminum oxide by using a new, stainless steel wire brush on the joint.

Question: Is it possible to weld the type of cast aluminum most Asian automobile wheels are made of? I want to cut a lip off the edge of one rim and weld it onto another. What do I need to do this?
Answer: Give up on this idea and buy a new wheel. The cast wheel is heat treated to obtain a high strength and you have no way to do this. Your weld and its heataffected zone will be significantly weaker than the rest of the wheel, even to the point of being dangerous.

Question: Can SAE1144 steel be welded? If so, what should I use?
Answer: This material is a "free machining" grade of steel and therefore is considered unweldable because its sulfur content is 0.08% to 0.13%. Sulfur causes solidification cracking (also referred to as "hot cracking") in welds and is characterized by a crack at the weld bead centerline. Because sulfur has a low melting point, it is the last material to solidify. Therefore, it gets swept into the middle of the weld during solidification. The shrinkage stress that occurs before the material is fully solidified is what causes the centerline crack.

Good rules of thumb for sulfur content in steel weldability:

  • 0% - 0.05% sulfur makes for good weldable steels.
  • 0.05% - 0.10% sulfur is difficult to weld without cracking.
  • Greater than 0.10% is unweldable.

Because SAE 1144 steel has a relatively high sulfur content, my advice is don't attempt to weld SAE 1144 steel.

This column is sponsored by Penton and the Lincoln Electric Co, Cleveland. Dave Barton is a senior welding engineer in the Application Engineering Group of The Lincoln Electric Co. He oversees welding procedure development for both new technology and existing products, performs failure analyses for customers, and serves as a consultant on welding application problems. Barton has been with Lincoln Electric for 21 yr. Send your questions for Mr. Barton in care of WDF by e-mail to: askdav@penton.com.