Improvement in grain refinement efficiency of Mg–Zr master alloy for magnesium alloy by friction stir processing

Abstract

Abstract Previous studies have proved that the zirconium (Zr) alloying and grain refining performance of a Mg–Zr master alloy on Mg alloy is closely related to the distribution of Zr particle size, and a Mg–Zr master alloy with more Zr particles in size range of 1–5 μm exhibits a better refining efficiency. In this paper, friction stir processing (FSP) was used to modify the Zr particles size distribution of a commercially available Mg–30 wt.%Zr master alloy, and the subsequent grain refinement ability was studied by trials on a typical Mg–3Nd–0.2Zn–0.6Zr (wt.%, NZ30K) alloy. It is found that plenty of large Zr particles in the as-received Mg–30%Zr master alloy are broken by FSP. Grain refinement tests reveal that the refining efficiency of Mg–30%Zr alloy is significantly improved by FSP, which is attributed to the better distribution of Zr particles. The refinement effect by adding 0.6% FSP-ed Mg–30%Zr is approximately equivalent to that by adding 1.0% as-received Mg–30%Zr. Due to the easy and convenient operation of FSP, this study provides a new method to develop a more efficient Mg–Zr refiner.