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

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.