Heat treating aluminium-silicon-magnesium castings - in two stages to improve dimensional stability

摘要

Heat treatment is to dimensionally stabilise hypoeutectic Al-Si-Mg alloy castings esp. large sand castings. The treatment involves >=2 stages. The first is holding at 300-340, esp. 320 degrees C for 4-8, esp. 6h and the second is holding at 210-240, esp. 225 degrees C for 6-10, esp. 8h. The heat treatment improves the machinability and esp the dimensional stability during machining or subsequent use notably when the parts are exposed to temps. above room temp. for long periods. The parts are used in machines with rotating parts where the play between rotating parts has to be as small as possible for reasons of fluid tightness.