Study on the Grain Refinement Behavior of Mg-Zr Master Alloy and Zr Containing Compounds in Mg-10Gd-3Y Magnesium Alloy

The effects of Mg-Zr master alloy and a potassium fluozirconate (K₂ZrF₆) salt mixture (KSM) on the grain refinement behavior of Mg-10Gd-3Y magnesium alloy were studied. The results show that the Mg-10Gd-3Y alloy is well refined by Mg-Zr or KSM. The characteristic micro structure feature of the alloy refined by Mg-Zr master alloy is the Zr-rich cores that exist in most grains, while the Zr-rich cores are not observed in the alloy refined by KSM. It is suggested that the grain refinement mechanisms of zirconium in the two cases are different: the Zr released from Mg-Zr master alloy works by adding heterogeneous nucleants, while the Zr produced from the in-situ reaction between Mg melt and K₂ZrF₆ works by restricting grain growth. Compared with the Mg-30.wt%Zr master alloy, the KSM refiner shows much longer fading time during melting.