The Search Of New Cast Magnesium Alloy

AZ64 cast Mg alloy was systematically studied in this dissertation. The microstructure was first confirmed. And the effect of alloying elements on the microstructure and properties were then studied, the discussion and analyse on the phase formation by adding Sb and RE in the course of solidification were found to influence the mechanism of microstructure formation, thereby we found out the cause of the elevation of the properties. The appropriate heat treatment could adjust the microstructure and improve the properties effectively, and after T6 heat treatment, its properties could excel AZ91 Mg alloy markedly. Modification treatment could refine the grain clearly. The confirmation of the new ternary Mg21(Al, Zn)17Φphase was ensured by the ternary Mg-Al-Zn phase diagram, X-Ray diffraction and EDAX spectrum in the ESEM. And combined with the binary phase diagram of Mg-Al, we could ensure that there existed Mg17Al12β phase, so the microstructure of the AZ64 cast Mg alloy was constituted by α-Mg matrix, Mg17Al12 βphase, and Mg21(Al, Zn)17 Φphase. Al element is one of the compositive element of Mg17Al12β phase, which increased the strength and hardness at room temperature. In order to resolve the corrosion resistence, Mn was added. Zn can combine with Al to improve the room strength but we should notice the cooperation of the content of Al and Zn. During the solid solution treatment (SST), the second precipitate phases were dissolved nearly completely after 16 hours of SST at 370℃, but the remnant phase such as Mg3Sb2 was steady. The dissolved phases precipitated again along the grain boundaries when continuous aged at 180℃ for 16 hours, which changed the shape and distributing of the precipitate phase to satisfy the mechanical properties.