Hardness control of Al-Si HPDC casting alloy via microstructure refinement and tempering parameters

Analysis of the effect of microstructure refinement, water quenching, natural ageing as well as T5 and T6 tempers onmacro-hardness development of the hypereutectic HPDC Al-Si based alloy was performed. Duration of casting holding at room temperature after its removal from the die, and prior to subsequent temper operation had a measurable effect on casting macro-hardness. Such finding underlined the need for tighter control of parts handling between casting and heat treatment operations. Water quenching after casting de-molding operation increased alloy macro-hardness in naturally aged as well as T5 temper conditions but did not have any effect on macro-hardness after T6 treatment. T5 temper carried out after casting de-molding and water quenching from 380 degrees C enabled on average approximately 9 to 19% macro-hardness increase as compared to the T1 condition. Microstructure refinement had a minor effect on macro-hardness increase but the measurements of the alpha-Al matrix micro-hardness needed to be used to demonstrate this effect. Compared with T6, the T5 temper offered up to approximately 20 to 60% shorter process duration and could offer potential cost reduction gains achieved at the expense of lowermacro-hardness. Microstructure refinement did not have the effect on T6 casting macro-hardness. (C) 2016 Published by Elsevier Ltd.