Deformation Behavior Of Spd Ultra-Fine Grained Mg-Zn-Y-Zr Alloys Processed By ECAP

Equal channel angular pressing (ECAP) was performed on the extruded Mg-5.0wt%Zn-0.9wt%Y-0.2wt%Zr magnesium alloy containing quasicrystallines at the temperature from 175℃to 300℃for different passes. The microstructure of the as-extruded magnesium alloy and ECAPed ultra-fine grained magnesium alloy were examined by means of optical microscopy (OM), scanning electronic microscopy (SEM) and transmission electron microscopy (TEM). Texture development of the as-extruded magnesium alloy and ECAPed ultra-fine grainrd magnesium alloy was investigated by neutron diffractometer and EBSD(Electron back scattered diffraction). Tensile deformation behavior of the as-extruded magnesium alloy and ECAPed ultra-fine grained magnesium alloy at ambient temperature were investigated. Both the compressive and tensile deformation behavior of the as-extruded magnesium alloy and the 200℃-8pass ECAPed ultra-fine grained magnesium alloy at ambient temperature and elevated temperatures under different strain rates were investigated and the deformation mechanism was discussed.The as-extruded Mg-Zn-Y-Zr alloy had an initial grain size of about 5μm and bands of quasicrystal phase parallel to the extrusion direction. During ECAP, the quasicrystalline phases were broken and dispersed in the matrix and some nano-quasicrystallines precipitated from the matrix. After the extruded alloy was subjected to 8-pass ECAP at 200℃, the grain size was refined to about 0.5 um. With increasing of ECAP passes, the yield stress of the alloy was decreased, while the elongation to failure at ambient temperature was effectively improved. After 8-pass ECAP at 300℃, the elongation to failure of the alloy reached 35%, which was three times of that of as-extruded alloy and was considered to be resulted from the grain refinement and the texture modification during ECAP.The compressive deformation showed that due to the significant refinement of the grain size and the broken and dispersed quasicrystalline phases could effectively prevented the grain from growing, so the ECAPed ultra-fine grained magnesium alloy exhibited better deformability than the as-extruded magnesium alloy. During the compressive test at 150oC, the ECAPed alloy specimens...