What is Cast Aluminum
Cast Aluminum is used for making engine blocks, motors casing and many other parts in automobiles due to their lightweight compare to steel. Aluminum alloys are classified into two main types: casting alloys & wrought alloys. Aluminum castings are mostly made by pressure-die, and molding methods. Casting alloys also have a system of four-digit designations as given in below Table:
TIG or MIG welding of Aluminum casting
Welding of aluminum casting can be carried out using TIG welding or GMAW (MIG Welding). The selection of the welding wire for aluminum is based on the casting type or its series i.e. 2000 series of 3000 and so on.
Generally, ER4043 is good to weld many types of aluminum casting used in engine blocks using TIG or MIG welding. ER5356 is another option. TIG or MIG with AC polarity shall be used for any type of aluminum welding either new welds or repair welds.
Stick welding of Cast Aluminum
The surface cleanliness and removal of the oxide layer is one of the most important pre-requirement for welding aluminum. Oil, or other organic materials, as well as a heavy oxide film on the rod, will interfere with the coalescence of the weld and also are sources of porosity. Because of this, it is necessary to clean the welding rod before putting them in the weld.
Stick welding of cast aluminum is not much popular & stick welding electrodes are available in limited types in the market.
Preheating for aluminum casting welding
Preheating is not required for thin aluminum but usually as cast aluminum is having a high thickness, it is advised to preheat it before welding. As aluminum has high heat conductivity, heat dissipates very fast so preheating around 200-250 Deg F is good otherwise you can have a lack of fusion issues. Interpass temperature is not an issue for aluminum welding.
Preheat is recommended for thicker sections or whenever sufficient penetration can not be achieved due to the high thermal conductivity of the aluminum.
So, if any of the above issues are being faced, a preheat temperature of 150 to 200°C can be applied. Also, when repairing 5XXX (Al-Mg) grades, it can crack in the weld or HAZ area. Following a preheat in these conditions is very beneficial to mitigate the cracking inter-alia to using the right filler wire.
TIG- MIG welding parameters for welding
TIG welding parameters for cast aluminum welding are given in the below table.
MIG welding parameters for cast aluminum repair are given in the below table.
TIG welding of aluminum is welded using AC polarity mostly with pure argon (AWS A5.32 or ISO 14175 – I1) as gas shielding. Sometimes, helium (AWS A5.32 – I2 gas) is mixed with argon gas for gas shielding up to a maximum of 25% to enhance the arc efficiency to melt thicker aluminum parts.
Helium increases the arc heat thus improving the welding penetration when welding aluminum alloys. Pure aluminum tungsten electrodes are used for TIG welding of aluminum to give improved cleaning action during welding.
DCEP polarity is also used for aluminum welding but not much. It is good for welding thin sheet aluminum materials but it requires thicker tungsten electrodes to carry the high current needed for aluminum welding.