Chapter G.9 - Aluminium casting alloys

Abstract

Experience shows that copper-free aluminium casting alloys generally have better pitting corrosion resistance than wrought alloys processed by rolling or extrusion. This would be due to the fact that the oxide film of the ‘foundry skin’ is more resistant than that of wrought semi-finished products. In general, copper-free silicon aluminium casting alloys with or without magnesium have very good resistance to atmospheric corrosion. The corrosion resistance of aluminium casting alloys depends on several parameters: metal source – primary or recycled metal, casting mode, metal quality, modification route used for aluminium–silicon alloys, copper content, iron content. Aluminium–silicon–magnesium castings alloys and wrought aluminium–magnesium alloys have excellent stress corrosion resistance. Copper has a very strong influence on the filiform corrosion resistance of A356.0 alloy. Aluminium–copper casting alloys have many similarities with wrought alloys: the propagation of stress corrosion cracking is intergranular, the high content of certain alloying elements such as zinc, magnesium and copper, separately or together, sensitizes the cast alloys, silicon-containing and over-aged copper-containing alloys have excellent resistance to corrosion and stress corrosion, residual or sometimes in-service stresses are the main cause of stress corrosion.