Influence of Zr, Cr and Sc alloying on the microstructure and mechanical properties of a Al-Mg-Si casting alloy

Abstract

The aim of this work is to investigate the influence of Zr, Cr and Sc alloying elements on a Al-5Mg-2Si-0.6Mn alloy produced using high-pressure die casting technique (HPDC). Previous study has shown a promising improvement of the mechanical properties in die-casting alloys doped with Sc. However, taking into account the high price of the Al-Sc master alloys and of pure Sc (even a small addition of it can increase the price of the alloy significantly), an important motivation of this research is to explore the possibility of full or partial Sc substitution by Zr and/or Cr. Thus, the first part of this research deals with the effects produced by chosen alloying elements in the as-received alloys. As compared to the wrought Al-Mg-Si alloys, where the main strengthening effect is produced by precipitation hardening through formation of Mg2Si nanoscale particles, here the effect induced by solution strengthening takes place. Despite the fact that HPDC alloys are not recommended to heat treated with high temperatures (T6) due to the enhanced porosity, several temperature modes have been proposed in order to reach the strengthening effect through formation of Al3Sc and Mg2Si strengthening particles. Such a combination of precipitates is not straightforward due to the different temperature of formation of these particles. Nevertheless, it was thought to be possible to combine two mechanisms: precipitation hardening and solid solution strengthening; or alternatively to find the optimal heat treatment for the investigated alloys. With this task the second part of current work deals.