Effects Of Y On Microstructure And Mechanical Properyies Of AZ31 Alloy

AZ31 alloy is one of the most widely applied commercial deformation magne -sium alloy. In this experiment, the preheating temperatures for metal mould casting die and squeezing casting die are 265℃, The dwelling time for squeezing casting is 300s and specific pressure is 122Mpa; Extrusion temperature is 425℃, with extrusion ratio 12.76 and extrusion deformation speed 2mm/s. AZ31 alloy were prepared in two different ways: one is the hybrid method of metal mould casting and extruded deformation; the other is to combine the squeezing casting with extrusion deformation. The effects of rare-earth element yttrium(Y) on microstructure and mechanical properties of AZ31 alloy were investigated by optical microscopy(OM), X-ray diffraction(XRD) and tension test at room temperature.Studies show that the grain size of AZ31 alloy reduces gradually with the increase of Y content. While the content of Y reaches up to 6.0 wt. %, the microstructure appears no evident change; Compared with the AZ31 alloy prepared by metal mould casting, the microstructure of the AZ31 alloy prepared by squeezing casting with the same content of rare earth Y is refined significantly, the distribution of the intergranular phase is more uniform, the strength and plasticity are enhanced. When 1% - 4%( mass fraction) rare earth yttrium(Y) is added to AZ31 alloy, with the increase of the element Y, the brittle phase Al2Y is formed, which offseted the effect of the addition of Y and caused the mechanical property of AZ31 alloy to drop greatly; when the content of Y is up to 6.0 wt. %, the structure is not refined, and more brittle phase Al2Y is formed, so the plasticity of alloy reduced obviously.The grain of AZ31 alloy is refined by dynamic recrystallization after extrusion. The addition of Y hinders the dynamic recrystallization. Compared with the AZ31 alloy prepared by the combined method of metal mold casting and extruded deformation, the microstructure of the AZ31 alloy prepared by the combined way of squeezing casting and extruded deformation with the same content of rare earth Y has more uniform structure and higher plasticity. Typical base texture is formed in extrusion deformation structure of AZ31 alloy. The (0002) crystal face parallel to direction of extrusion(ED direction) has formed during extrusion deformation process of AZ31 alloy, the base texture increased, with the addition of rare earth yttrium(Y); In addition, the base texture of the AZ31 alloy prepared by the combined way of squeeze casting and extrusion deformation with the same content of rare earth Y is enhanced significantly, compared with the AZ31 alloy prepared by the combined method of metal mold casting and extrusion deformation.