Effect of solution treatment on microstructure and hardness of rheo-forming AZ91-Y alloy.

The microstructure and hardness of rheo-forming AZ91-Y alloy before and after solution treatment (ST) have been investigated by means of optical microscope (OM), scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Vickers. The experimental results showed that the β-Mg₁₇Al₁₂ phase of alloy was nearly dissolved after ST for 5 min. With the increasing of ST duration to 28 h, both the primary and secondarily solidified α-Mg grains faded away. At the same time, the alloy exhibited a much smoother surface due to the diffusion of solute atoms (Al). During ST, the thermal stable phase of Al₂Y produced by ultrasonic vibration retained its size and morphology. As the ST duration was increased, the alloy hardness decreased sharply at first, and then gradually reached a minimum level. The alloy's appropriate ST duration at 410 °C was approximately 28 h. [ABSTRACT FROM AUTHOR]