How to Weld Cast Aluminum With a MIG

Always wear proper safety equipment such as hood and gloves when welding.

Welding on cast aluminum material with a MIG welder is done all the time, but there are a few things to keep in mind. First, welding aluminum requires a lot of heat, so you'll need a good 220-volt unit that can bring high amperage. Second, aluminum is very picky about how it welds when it is dirty, so a thorough cleaning is necessary before any MIG aluminum welding.

Things You'll Need

• 220-volt welder
• Spool gun
• Aluminum wire
• Argon tank

Instructions

1. Clean the surface of the aluminum with a wire brush and a strong solvent like acetone. Aluminum oxidizes extremely easily, and unlike the rust on steel, it is not as readily visible to the naked eye. It is imperative that the surface be as clean as possible so that the MIG gun can strike a decent arc when power is applied. Don't forget to clean the area where you intend to attach the ground clamp, as well.

2. Install aluminum wire into the MIG machine. It is not possible to weld aluminum material with solid steel or flux core wire, as they will not bond well with the aluminum and the weld will not be very strong. Your MIG welder will need to have a spool gun installed as well, because the aluminum wire is too soft to push from the machine, and therefore must be pulled toward the gun. Also, you must use pure argon in the welding tank for the aluminum weld to be fully protected for welds up to one half-inch thick. For materials thicker than a half-inch, use a 50/50 helium/argon mix so that the spark stays hotter for deeper penetration.

3. Ensure that the voltage and amperage settings on your MIG welder are set to high. You'll need at least 180 amps to weld the aluminum properly, and thick material will require more. If your welder is a 180- to 210-amp unit, you should do just fine. If the aluminum is approaching one half-inch thick or more, it is strongly recommended to preheat the material with a torch beforehand so that the MIG welder can penetrate as it should. Normally, a 300- to 400-degree preheating temperature will work fine.

4. Weld the material. It is very important to take your time and move slow when welding aluminum, because the material dissipates heat very quickly, and will cause the weld to be weak if the gun is moved too quickly. Move in a slow, back and forth or "C"-shaped motion with the tip of the gun, which should be angled toward the direction of the weld so that best penetration is achieved.

References

• Welder's Handbook, RevisedHP1513: A Guide to Plasma Cutting, Oxyacetylene, ARC, MIG and TIG Welding; Richard Finch; 2007