Effect of Heat Treatment on the Microstructure and Mechanical Properties of the Friction Stir Processed AZ91D Magnesium Alloy

We study the microstructure and mechanical properties of friction stir processed AZ91D cast magnesium alloy under various conditions of heat treatment. It is shown that, in the initial as-cast state, the structure of the alloy contained a continuously networked β-phase with an average grain size of 150 μm. The friction stir processed (FSP) specimens had an average grain size of 12 μm and smooth grain boundaries. The subsequent heat treatment of the FSP specimens at various temperatures between 150°C and 250°C led to the appearance of numerous particles of the β-phase. The FSP specimens heat-treated at 200°C had finer grains, a larger number of fine particles of the β-phase, and better mechanical properties than any other specimens.