Always clean aluminum base material before welding to remove the oxide layer. Use a stainless steel wire brush used only for cleaning aluminum. A biodegradable aluminum cleaner and brightener is also available, try Weldmark WM781 for rapid and effortless cleaning and removal of aluminum oxides, grease and dirt from aluminum before welding.
The most common wire type for aluminum mig welding is ER4043 for all purpose work. ER5356 is a stiffer wire, easier to feed, and is used when more rigid, higher strength weld properties are needed. If you experience wire feeding problems with aluminum, one thing you can try is a contact tip that is one size bigger than your wire. The larger hole size in the contact tip will allow for heat expansion of the welding wire.
The best feeding of aluminum wire is done with a spool gun. If you cant use a spool gun, use the shortest gun possible and keep the gun as straight as possible. Use only argon shielding gas. Use a push gun technique when welding aluminum.
Why is preheat sometimes required before welding?
Preheating the steel to be welded slows the cooling rate in the weld area. This may be necessary to avoid cracking of the weld metal or heat affected zone. The need for preheat increases with steel thickness, weld restraint, the carbon/alloy content of the steel, and the diffusible hydrogen of the weld metal. Preheat is commonly applied with fuel gas torches or electrical resistance heaters.
All welding machines use cables, lugs and work clamps. If you ensure to use the correct size of cable (based on the maximum output of your welder), the cables and fittings will last considerable longer and provide for cleaner welds. A good weld requires a good ground, make sure all ground clamp and machine connections are tight and secure.
Stickout means the distance from the mig welding tip (contact tip) to the arc. Not the distance from the gas nozzle to the arc! Too long a stickout will soften the arc and make the weld pile up. When welding, the tip should be recessed 1/8 from the gas nozzle and keep the stickout no more than 3/8 to ½ to the work piece.
The contact tip is the only place that MIG wire gets its power. A dollar-a-day contact tip change will save you hundreds of dollars in grinding or re-work. Change your tip daily for stable feeding, reduced spatter, and a smooth weld.