Aluminum Castings repaired:
Aluminum Alloy castings scrapped in the foundry since of surface defects and lack of dimensional integrity can be recovered by welding apart from if they present massive porosity.
Gas tungsten arc welding (GTAW) with high frequency stabilized Alternating Current is usually used to fix sound castings. Inclusions are supposed to be disallowed by taking care to avoid touching the surface with the pure tungsten electrode.
Argon with or without helium can be used as a shield. Helium helps produce a hotter arc if essential. To arrange for welding one should remove defects, particularly cracks, by dry chipping with a rounded tool or by hand milling, to get a smooth area. One ought to by no means attempt to weld on the original casting outside rough surface with no first removing the oxidized coating.
Removal of oil and grease is performed using steam degreasing or clean solvents. Use of acid etch is not suggested. If impregnation was applied, it should be removed previous to welding. A spotless stainless steel wire brush should be used to clean thick oxide layers just earlier than welding.
Filler material alloy is regularly the same as that of the casting. Preheating is wanted only in outstanding cases to conquer difficulties.
On correctly prepared surfaces of sound castings, with oxide coatings thoroughly cleaned, one should be able to weld as with no trouble as on wrought alloys. It would be fine practice to look for cracks in the weld by using penetrant inspection.
Radiographic check may be necessary by contract in sure cases.
If the original castings are to be warmth treated, also the fixed ones should go after the same procedure. Weld repairing of heat treated casting would impair their mechanical properties.
The possibility of repair of aluminum alloy castings that were previously heat treated and machined is doubtful since of stresses and deformations likely to develop during welding.
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