An empirical analysis of trends in mechanical properties of T6 heat treated Al-Si-Mg casting alloys

The Al-Si-Mg family of alloys is typically used in the T6 heat treated condition for high integrity casting applications, There are several variables that can influence the tensile properties of these alloys besides the actual ageing treatment employed. These are alloy composition, particularly Mg and Fe content, and secondary dendrite arm spacing or SDAS, Tensile data from samples covering a wide range of Mg content (0.3-0.7%), Fe content (0.05-0.20%), SDAS (20-60 mu m) and two ageing treatments (under-and peak-aged), have been collected and analysed empirically. Concise relationships have been determined for yield strength, ultimate tensile strength and elongation to fracture in terms of one or more of the experimental variables. The observed trends are explained in terms of basic metallurgical principles and the predictive use of the empirically-determined equations is qualified. A comparison of experimentally determined properties and those calculated using the derived relationships highlights some important and clear trends.