Microstructures And Tensile Properties Of Hot-Extruded Mg-5%Zn-0.6%Zr-3%Gd Alloy

As a lightweight structural material, magnesium alloys have been used in industrial production more and more widely. With a sharp increase in the usage amount of magnesium alloys, higher mechanical properties are required for magnesium alloys. Obviously, the development of wrought magnesium alloys can meet the requirements of mechanical properties on structural components, and thus, magnesium alloys can be applied in industrial fields more broadly.The tensile mechanical properties of hot extruded Mg-5%Zn-0.6%Zr-3%Gd alloy were investigated. The tensile strengthσb, yield strengthσ0.2 and fracture elongationδof the alloy with different extrusion ratio and different heat treatment states were determined. The microstructure evolution of the Mg-5%Zn-0.6%Zr-3%Gd alloy caused by hot extrusion and heat treatments was studied. In addition, the morphologies of the tensile fracture surfaces of the alloy were observed and analyzed by means of SEM. Furthermore, the effect of different extrusion ratio and different heat treatment states on the mechanical properties and fracture characteristics of the alloy were determined.The results show that the variation of the grain size of the Mg-5%Zn-0.6%Zr-3%Gd alloy extruded with different extrusion ratio is noticeably. With increasing the extrusion ratio, the size of both matrix grains and second phase particles of the alloy gets better refined, and the tensile strength, yield strength as well as fracture elongation of the alloy also increase. The heat treatment also has great influence on the microstructures and mechanical properties of the magnesium alloy with as-extruded state. When the hot extruded alloy was carried out with direct aging treatment (T5), no grains grow up, and the microstructures of the alloy were homogenized. In addition, some strengthening phases precipitate in the grains and along grain boundaries. Therefore the comprehensive mechanical properties of the Mg-5% Zn-0.6% Zr-3% Gd alloy at room temperature can be well improved. After solid solution plus aging treatment (T6), the grains of the alloy grow up, but a lot of dispersed fine second phases also precipitate. Thus compared with the alloy with as-extruded state, the strength of the alloy with T6 state exhibits no significant change, but the fracture elongation of the alloy gets improved obviously.The morphology analysis on the fracture surfaces of the Mg-5%Zn-0.6% Zr-3%Gd alloy with different states shows that the magnesium alloy exhibits the mixed fracture characteristics of both brittle and ductile fracture. More cleavage facets exist in the tensile fracture surfaces of the alloy with as-extruded state, and the fracture mode of the alloy is mainly brittle fracture. With increasing the extrusion ratio, the number of the tearing edges increase, and the ductile fracture degree gets improved. A large number of tearing edges and dimples exist in the tensile fracture surfaces of the alloy after heat treatments, and the fracture mode of the alloy is mainly ductile fracture.