Microstructure And Mechanical Properties Of Magnesium Alloy By Caliber Rolling

Magnesium（Mg）and its alloys are the usuable lightest structure materials up to now,and it comes more and more popular in recently due to their low density,high specific strength and stiffness,excellent impact resistance and damping properties,good electromagnetic shielding performance and eco-friendly.Thus,Mg usually known as"the green engineering materials of 21^st century".However,there are also lots of problem such as low strength,insufficient plasticity in low temperature and inveitable corrosion issues.Previous researches shown that multi-pass caliber rolling as a noval severe plastic deformation（SPD）can be used to manufacture ultrafine-grained steel and titanium alloys.The more strain accumulated,the more refined grain can be obtained.Besides,the second phases are also crushed and uniformly dispersed along the rolling direction during the deformation.And which in turn,the related mechanical properties would be enhanced significantly.Therefore,the study of caliber rolling magnesium alloys has important theoretical guidance and practical significance for high-performance magnesium alloys.Thus,our research objective is microstructure and mechanical properties of both pure Mg and AZ31 alloy by utilization of caliber rolling.In particular,the effect of caliber rolling parameters（i.e.rolling reduction,temperature and speed）on the microstructure and mechanical properties of Magnesium alloy were systematically investigated.In case of pure Mg,with increasing of rolling pass,the as-cast pure Mg with coarse grain was completely changed into fine structure due to occuration of dynamic recrystallization（DRX）.In addition,the equix grain with uniform microstructure can be observed clearly.Moreover,the mechanical properties of caliber rolled pure magnesium was improved significantly.For instance,tensile yield strength,tensile strength,compressive yield strength,and elongation at reduction of 79%were determined to be 115 MPa,203 MPa,97 MPa and 10.63%,respectively.The similar trend can be found in case of AZ31 alloy,that average grain size decreases from 529μm to 8.25μm with the accumulation of deformation.In addition,the tensile yield strength,the tensile strength and compressive yield strength of as-rolled AZ31 alloy at reduction of 86%were 223 MPa,313 MPa and 230 MPa,respectively,which improved dramatically compared with as-homogenizaed state.However,the elongation degraded a little bit from rolling pass of 7 to 10 with increase of accumulated strain.In order to know the effect of rolling temperature and rolling speed,the AZ31 alloy was caliber rolled at various deformation temperature（250?C,300?C and 350?C）and rolling speed of 0.2 m/s and 0.5 m/s,respectively.We found that the microstructure was depended more sensitively on the rolling temperature than that of rolling speed.Specifically,fully DRX and fine grain microstructure can be obtained at low temperature with slow speed.Furthermore,the influence of rolling temperature on mechanical properties at speed 0.2 m/s.was not very impressed.In case of rolling at 0.5 m/s,the tensile yield strength,the tensile strength,the compressive yield strength and elongation of AZ31 alloy decreased gradually with the increase of the rolling temperature.According to our results,the optimal caliber rolling parameters of AZ31 magnesium alloy are as follows:rolling temperature of 350?C,rolling speed of 0.2 m/s,which shown tensile yield strength:320 MPa;tensile strength:356MPa;compressive yield strength:321 MPa;elongation:13%,respectively.