The effect of die geometry on the microstructure of indirect squeeze cast and gravity die cast 7075 (Al-6.2Zn-2.3Cu-2.3Mg) wrought Al alloy

摘要

The indirect squeeze casting process has beenused to cast a 7075(Al-6.2Zn-2.3Cu-2.3Mg) wrought Alalloy to near-net shape with excellent die replication. Defectswhich occur with gravity casting, in particular(1)shrinkagepipe, (2) macro-porosity and(3) hot-tearing, are largelyremoved by squeeze casting, although regions of macro-porosity can re-appear when thick sections are fed throughsubstantially thinner sections. Squeeze casting results in aconsiderable refinement of microstructure compared togravity casting due to a marked decrease in solidificationtime. The decrease in solidification time is caused by intimatecontact between the pressurised melt and the die, which leadsto an increase in the heat transfer coefficient. Decreasing thesection thickness also results in a refinement of themicrostructure due to a reduction in solidification time.