Improving casting performance by extending feeding action in long-freezing range cast aluminum alloys

摘要

The dispersed form of porosity observed in long-freezing range cast aluminum alloys has important effects on their mechanical behavior. In particular, ductility, fracture toughness, fatigue crack initiation and propagation are affected. Consequently, there is an ongoing interest in characterizing the form and distribution of such porosity in castings destined to become critical components in aerospace and automobile systems, alike. In the light of this interest, the porosity patterns associated with simple bar and plate-type castings have recently been reexamined. Quite apart from the relative moduli and volumes of castings and the risers feeding them, the local pressurization of risers was pointed out as being a further important factor in controlling such porosity profiles. The present paper discusses recent work on the effects of microporosity on mechanical behavior, and goes on to discuss the background to local pressurization, and indicates how it enhances the effect of parameters describing the local thermal environment in the casting, such as the popular Niyama criterion.