"An Inverse Distribution of Hardness in T5-Heat Treated Al-Alloy Permanent Mold Castings"

T5 열처리한 Al합금 금형주조품에서 경도의 역분포현상

Aluminum alloy permanent mold castings often exhibit in as-cast or T5-heat treated state an inverse distribution of hardness, i.e. thinner sections have lower hardness than thicker sections. This phenomina is explained by measuring the cooling curves in a test casting in an Aluminum piston alloy (AC8A or A332). Thinner sections solidify faster but later cooles down more slowly than thicker sections in temperature range where coarse precipitation of supersaturated elements can take place. The precipitation rate of $Mg_2Si$ phase in A332 alloy seems to be maximum at around $490^{\circ}C$.