Microstructure and mechanical properties of as-quenched Mg-Gd-Zr alloys

Mg-xGd-0.6Zr (x= 2, 4, 6, mass fraction) alloys were prepared by semi-continuous casting process. The effects of Gd content on the microstructures and mechanical properties of Mg-xGd-0.6Zr alloys were studied and the solid solution treatment process of Mg-6Gd-0.6Zr alloys was optimized. The microstructures and mechanical properties of all the studied alloys were analyzed by optical microscope, X-ray diffraction, scanning electron microscope equipped with energy dispersive spectroscope and micro-hardness tester. The results show that the grain size slightly decreases with increasing Gd content and there is a close linear relationship between Gd content and micro-hardness of Mg-xGd-0.6Zr alloys. The second phases Mg(2)Gd and Mg(3)Gd formed due to non-equilibrium solidification during the casting process can be transformed into equilibrium phase Mg(5.05)Gd which can dissolve into alpha-Mg solid solution phase at solution temperature of 460 degrees C. The optimized solid solution treatment of Mg-6Gd-0.6Zr alloy is (300 degrees C, 6 h) + (460 degrees C, 10 h).