Solidification and Heat-treatment Conditions Affecting the Tensile Properties and Fracture Feature of an Automotive AlSiMg Alloy

Abstract

In this work, a study on the interrelationship between the solidification and heat-treatment processes parameters with tensile properties and fracture feature was performed with an automotive AlSiMg alloy. For that, samples of the horizontally solidified Al7Si0.3 Mg (wt.%) alloy were subjected to the T6-heat treatment, and tensile tests were performed on both investigated samples, under conditions established from the literature. The solidification conditions such as growth and cooling rates and the secondary dendritic spacing (VL and TR and λ2, respectively) and their effects on the ultimate tensile strength (σUTS) and elongation (E%) were evaluated. Higher σUTS values were observed in the heat-treated samples and finer microstructures resulted in a better E% performance. Analysis by SEM/EDS fractography on both samples showed a mix between brittle and ductile fractures, constituted by cleavage facets, secondary cracks, facets covered with micro-voids, tear ridges and dimples. This allowed the deduction of the occurrence of a transition of a transition from ductile to brittle fracture along the solidified ingot as well as the predominance of brittle fracture in the heat-treated samples.