The Research On The Mg-Ca Alloy And Microstructure Evolution By Heat Treatment

Ca is light weight element with rich source. Mg-Ca alloy has the basic conditions to belight heat resistant alloy,has potentials to improve specific strength and this alloy would havea brilliant future.This paper mainly studies the effects of different Ca contents on binary Mg-Ca alloy, theeffect of other alloying elements (Bi,Zn),modification(Ho)and heat treatment on eutecticMg-Ca alloy. OM, XRD, SEM-EDS, presses machine, universal tensile machine and otherequipment were used to study the microstructure, phase composition and mechanicalproperties of each alloy.The results show that: the microstructure of Mg-Ca alloy are consist of α-Mg and Mg2Cabefore and after heat treatment.with the increases of Ca, the content of eutectic increases;when Ca reached16.5%the microstructure was almost consist of eutectic; After heattreatment at450℃and480℃for different time, the eutectic phase ofMg-Ca trans intoparticles, the longer treatment time and the higher the temperature, the greater the size thefewer number of the eutectic particles, and also the more rounded shape. After heattreatment(holding28h at450℃)and extrude(mould preheating at370℃and extrusion ratio is8.6),Mg-10%Ca turns out the tensile strength is242.36MPa, and elongation is3.15%,reduction of area is1.45%;Mg-16.5%Ca turns out the tensile strength is296MPa, andelongation is2.88%,reduction of area is1.12%.With Bi added,the primary phase increase,the primary further increase with the increase ofBi.After heat treatment at different temperature and different time, the eutectic phase ofMg-16Ca-6Bi trans into particles.After heat treatment(holding16h at440℃)and extrudeMg-16Ca-6Bi turns out the tensile strength is239MPa, and elongation is2.8%,reduction ofarea is0.8%.With Zn added,the primary phase increase and round shape.the eutectic phase ofMg-16Ca-3Zn trans into particles after heat treatment,primary phase has not obvious change.After heat treatment(holding16h at440℃)and extrude Mg-16Ca-3Zn turns out thetensile strength is180MPa, and elongation is3.77%,reduction of area is4.49%.With Ho added into Mg-Ca alloy,primary α-Mg phase trans into particles,when theaddition of Ho is1.0%,primary α-Mg phase trans into fine nodular,when further increaseHo,primary α-Mg phase increase.after heat treatment Mg2Ca trans into particles,and moreobviously with the increasing temperature and holding time,but the particles will grow and theshape will not normal when the amount of Ho is too much.After heat treatment(holding28h at450℃)and extrude Mg-16Ca-0.5Ho turns out the tensile strength is313MPa, and elongationis3.07%,reduction of area is1.33%.