Selection of temper and Mg content to optimise the Quality Index of Al-7Si-Mg casting alloys

Abstract

The extent to which the quality index,* Q, can be optimised through an adequate combination of Mg content and temper is discussed in the light of an analytical model relating Q to parameters of the flow curve. Published data describing the effect of DAS, Mg and Fe content and temper on the yield stress, tensile strength, ductility and quality index of experimental Al-7%Si-Mg alloys have been used for the analysis. The experimental data support the predictions of the analytical model which indicate that for a given temper there is a material strength that maximises Q. The results show that peak ageing can reduce Q in low ductility materials, also in agreement with the analytical model. Microstructural limits to the maximum attainable Q-value are discussed.

Keywords:

• Alloys A356 and A357
• Quality Index
• Tensile ductility
• Eutectic Si
• Age hardening
• Fe-rich intermetallic particles