Effect Of Y, Sb And Cd On Microstructure And Properties Of AM50Magnesium Alloy

As the lightest structural metallic materials, magnesium alloys have many unique and excellentproperties, such as high specific strength and stiffness, good damping capacity, excellentelectromagnetic shielding and machining characteristics, good processing properties and abundantresources, so they are widely used in various fields such as automobile, aerospace, electronic industryand national defense industry. AM50is one of the most broadly used magnesium alloys in industry.However, poor thermal resistance and corrosion resistance have limited its further applications. In thepresent work, the effects and mechanism of Y, Sb and Cd on microstructure and properties of AM50alloy were studied by many analysis and testing means, such as optical microscope （OM）, X-raydiffractometer （XRD）, scanning electron microscope （SEM） with energy dispersive spectrometer（EDS）, tensile testing, polarization and electrochemical impedance spectroscopy measurement, whichcould provide theoretic guidance on research and application of high strength and ductilityheat-resistant magnesium alloys.The results show that, suitable addition of Mn can refine the microstructure of Mg-5Al magnesiumalloy, change the precipitated phase morphology and meanwhile form the new phase Al8Mn5. Thetensile strength, elongation and impact toughness of Mg-5Al alloy rise at first and then drop while thecorrosion resistance increase with increasing Mn content. With0.3%Mn addition, the tensile strength,elongation, and impact toughness reach their maximum value simultaneously, which are190MPa、7.3%and21.1Jcm-2respectively and are7.9%、9.1%and9.3%higher than Mg-5Al alloy without Mnaddition, showing the optimal overall mechanical properties.The grain and precipitated phase of AM50alloy are significant refined with1%addition of Y,which leads to the improvement of mechanical properties and corrosion resistance. The tensilestrength at room temperature and150℃are increased by18.9%and23.2%respectively, meanwhile,the values of elongation at room temperature and150℃are increased by9.1%and11.7%respectively.However, the corrosion rate is decreased by27.6%.When adding Sb to AM50-Y alloy, the grain is refined obviously and a few dispersed phases YSb isformed, which promote the formation of fine, dispersed Al₂Y particles by providing the nucleationsites. With the increasing addition of Sb, the tensile strength, elongation at room temperature and150℃of Mg-5Al alloy rise at first and then drop while the corrosion resistance decreasemonotonously. With0.6%Sb addition, the tensile strength of the alloy at both room temperature and 150℃reach maximum values of257MPa and203MPa respectively, which are13.7%and12.8%higher with the alloy without Sb addition. Meanwhile, the elongation is9.9%at room temperature and11.9%at150℃, increased by15.9%and15.5%.The heat treatment experimental results of AM50-Y and AM50-Y-0.6Sb alloys show that, themicrostructure and mechanical properties of the alloys are obviously improved after solid solution andaging treatment. With the extension of aging treatment time, the micro-hardness of the alloys rise atfirst and then drop. The addition of Sb makes the peak hardness time bring forward.When adding Cd to AM50-Y-0.6Sb alloy, the microstructure of the alloy is refined and Cddissolves into the matrix of the alloy without formation of new phases. The tensile strength andmicro-hardness of the alloy increase slightly while the elongation and impact toughness improveobviously, and the corrosion rate and current density decrease with increasing Cd content. With1%Cd addition, the tensile strength and micro-hardness of the alloy reach their maximum valuesimultaneously278MPa and84.1Hv, increased by7.4%and4.9%compared with the alloy withoutCd addition. Meanwhile, the elongation and impact toughness increase13.1%and12.2%, reach to11.2%and30.3J·cm-2respectively, and the corrosion rate is only1.07mg·cm-2·d-1, decreased by42.5%compared with the alloy without Cd addition.