To perform MIG welding on aluminum, there are specific setting that you will need to use. Aluminum can conduct heat five times more faster than steel does. Because of this, aluminum welding require a higher wire feed speed than for steel welding.
For aluminum welding, the wire feed speeds are three or four times faster than those use for welding mild steel. Additionally, you must use an amperage chart to determine the correct amperage for the welding job. The correct amperage depend on the thickness of the aluminum that you are welding and the size of the wire that you use.
How to MIG Weld Aluminum
If you dont use the correct amperage for the job, you may encounter several problem with your weld. The thickness of the aluminum and the diameter of the aluminum wire that you use will determine the setting that you must use for your weld. For delicate work, you can use 0.030-inch aluminum wire.
For structural work, you may use 0.047-inch aluminum wire. You should match the diameter of the wire to the thickness of the aluminum to ensure that your welding process is repeatable. Additionally, you must use the correct type of aluminum filler wire for the type of aluminum alloy being welded.
For instance, ER4043 aluminum wire contain silicon that makes it easier to weld thin aluminum. For jobs that require high strength, ER5356 aluminum wire is use. Different aluminum alloys has different strengths, so the filler wire must match the requirements of the aluminum that is being welded.
The type of MIG gun that you use will also factor into your aluminum welding settings. Aluminum wire is soft, and aluminum wire can kink within the liner of the MIG gun. Standard MIG guns use liners made of steel.
Using steel liners can damage the soft aluminum wire if the distance between the aluminum wire and the MIG gun is greater than 10 feet. Using a spool gun can avoid this problem. A spool gun mounts the aluminum wire directly onto the MIG gun handle.
Using a spool gun is helpful for welding short run on thin aluminum sheet metal. For thicker aluminum metal or for welding at long distances from the MIG gun, you should use a push-pull system. A push-pull system has a motor mount within the handle of the MIG gun that pulls the aluminum wire.
This motor within the handle help to eliminate the friction that prevents aluminum wire from feeding smooth through the MIG gun. Aluminum naturaly develop an oxide layer called Al2O3. This oxide layer melts at a much higher temperature than the aluminum metal itself.
To weld aluminum, you must remove this oxide layer. To do this, use a dedicated stainless steel brush to scrub the oxide layer off of the aluminum metal. Wipe the aluminum metal with acetone before and after welding it.
Do not use iron brushes to clean the metal because the iron can rust the aluminum. Additionally, you must weld the aluminum within thirty minutes of having been cleaned with the stainless steel brush. The oxide layer will grow back on the aluminum if you wait to weld it for too long.
If the thickness of the aluminum metal is greater than 0.25 inch, the metal will naturaly act as a heat sink for the welding torch. To avoid this, preheat the aluminum to between 200 and 300 degrees Fahrenheit prior to welding. There are several defects that can develop during the MIG welding of aluminum metal.
Porosity can occur within the weld and is cause by water or incorrect gas settings for the weld. To avoid porosity during welding of aluminum metal, use 100% pure argon gas at a flow rate of between 20 and 30 cubic feet of gas per hour. Never use any CO2 gas mixes for welding aluminum metal because CO2 mixes is for welding carbon steel and not aluminum.
For thin aluminum metal, burn through can be an issue. This occurs when too much heat from the welding torch melt the thin metal. Use stitch welds or copper backing bar to avoid burn through for thin aluminum metal.
The sound that the welding torch makes while welding the aluminum metal can also reveal welding problems. A smooth hiss from the welding torch indicates that the welding torch is in the proper mode for welding aluminum metal, called spray transfer mode. A popping sound from the weld indicates that the voltage need to be increased along with the wire feed speed.
