High-Strengthening of Mg–5.5 mass%Y–4.3 mass%Zn Cast Alloy by Friction Stir Processing

High-strength Mg–Y–Zn alloy plate was obtained by friction stir processing (FSP) after casting. In this study, the Mg–Y–Zn alloy by FSP showed sufficiently high performance with low cost. As-cast material was held at 723 K for 95 h. It then showed a lamellar structure, which might have resulted from long-range periodic structure. However, this lamellar structure showed very low hardness, as did the as-cast material. Plates cut from heat-treated ingot were processed as single, overlapped double, and multiple pass FSP. After FSP, each processed materials was cut for microscopic measurement and hardness testing. Ultra-fine-grained microstructures are obtainable using the FSP. Micro-Vickers hardness tests for each pass result in the occurrence of strengthening for FSP of Mg–Y–Zn alloy. There was little change in grain size and hardness of pre-stirred zone by the next pass of stirring.