Study On The Microstructure And Properties Of Mg-Zn-RE(Y,Gd) Alloy Strengthened By Quasicrystal Phase

As the lightest metal structural material, magnesium Alloy has tremendous potential on many fields. But the weakness of low plasticity, bad heat resistance and corrosion resistance, which limited the application of magnesium Alloy. Quasi-crystal in magnesium Alloy shown a new way to reinforce the Alloy especialy in plasticity, and this made it become a new research hotspot.In this study, a trorough research including Alloy design, casting, homogenization, cogging, solid solution, deformation and aging was carried on the Mg-Zn-RE Alloy. Literature research shows, the composition fo the Alloy was set to Mg-3.7Zn-0.6RE(Y and Gd, at.%). After investigating the influence of the Gd/Y ratio and the cooling speed on the microstructure and phase compostion of the Alloy, the Alloy casted in water with the compostion of Mg-3.7Zn-0.3Y-0.3Gd was the optimal material for the following research.Homogenization could not solute the second phases completely, long time heat could even over burn the Alloy. During the homogenization process, twins and recrystallization emerged in the grains, multiple morphologies of preicipitations also formed. The transition process of the precipitations was studied.The as-cast Alloy was coged one pass and solid soluted. The solution was more effective than homogenization. Then the Alloy was forged for another two pass or extruded. Recrystalization happened during the deformation process and the second phases were crushed, quasicrystal particles also precipitated in these process. High-temp aging could made the precipitations adhered to the original second phases. Low-temp aging could activate the Mg-Zn aging precipitation sequence, the peak aging was180℃-20h and the hardness had the increasment of13%, which was71HB. The tensile strength of the extruded Alloy was316MPa, with the elongation of13%High-temp tensile test was carried out on extruded Alloy. Results show that the Alloy was strain rate sensitive material. Recrystalization also happened during the tensile process, which made the softening dominate. The Alloy show good plasticity with the elongation of70%to100%. The fractures were full of dimples and tear ridges.