7 - The processing and heat treatment of selective laser melted Al-7Si-0.6Mg alloy

Abstract

A heat-treatable aluminum alloy A357 has been chosen in this study to obtain further understanding about the relative density and mechanical properties after selective laser melting (SLM) and subsequent heat treatment at an experimental stage. Although as one of the most important groups of industrial cast alloys with a high strength/density ratio and good thermal properties, aluminum alloy A357 has been less frequently studied in the SLM field. Also, since conventional casting and SLM are two different techniques, it is not known whether SLM procedures and parameters for heat-treated alloys can be directly transferred to Al alloy A357. From this perspective, this chapter investigates the influence of the parameters for SLM and post heat treatment on the tensile behaviors of Al alloy A357. The possibility of omitting solution heat treatment was also explored, assuming that a supersaturated Al matrix with precipitate-forming elements Si and Mg is already achieved in the as-built condition after high-temperature laser melting and subsequent fast cooling. This refers to direct ageing in this work. Through the application of various combinations of laser fabrication and heat treatment parameters, the corresponding properties of the SLMed materials can be modified, mainly determined by fractographic studies via scanning electron microscopy. An open question is whether these post heat treatment parameters can be properly tailored to avoid issues such as residual stress development during SLM process, and in the meanwhile to maintain the enhanced mechanical properties compared to conventional cast counterparts.