Microstructure And Mechanical Properties Of Mg-Zn-Ca-Mn Alloy And Its Composite After Hot Extrusion

In this study,Mg-xZn-(4-x)Ca-0.5Mn(x=2.9,2.2,1.4,wt.%)alloys were designed and fabricated by adjusting Zn/Ca ratio with a total weight ratio kept at 4%.In addition,Mg-Zn-Ca-Mn alloy reinforced by 0.5 wt%Ti C nanoparticles were fabricated.The effects of different Zn/Ca ratios and the addition of Ti C_pon the microstructure and properties of as-cast and extruded Mg-Zn-Ca-Mn alloys were systematically studied.The results show that the dominant second phase in the as-cast Mg-2.9 Zn-1.1Ca-0.5Mn alloy was Mg Zn and changed from to Ca₂Mg₆Zn₃ as the Zn/Ca ratio decreased.After the homogenization treatment,Mg Zn phase was dissolved into the matrix,and the undissolved discontinuous net-like phase was Ca₂Mg₆Zn₃.With the addition of Ti C_p,the grains of all the as-cast nanocomposites were significantly refined,the second phase was Ca₂Mg₆Zn₃.The fine second phase diffusely dispersed in the Ti C_p rich area.With the decrease of Zn/Ca ratio,the yield strength(YS)of ZXM alloys was increased due to the improved effects of fine grain strengthening and Orowan strengthening,and further increased after homogenization.The addition of Ti C_p further enhanced the fine grain strengthening and improved the second phase distribution,resulting in the significant increase of YS in both as-cast and homogenized Ti C_p/Mg-Zn-Ca-Mn nanocomposites compared with its matrix alloy.After different extrusion processes,the grain sizes of Mg-2.2Zn-1.8Ca-0.5Mn alloy was significantly refined due to the occurrence of dynamic recrystallization(DRX).The dynamical precipitated phase was Mg Zn₂.The DRX grain size,DRX volume fraction and precipitates size of the alloy were gradually decreased with the decrease of extrusion speed or extrusion temperature,while the volume fraction of precipitates gradually increased.The extruded alloy exhibited a typical fiber texture<10-10>,and the texture density in the un DRX region was much higher than that in the DRX region.YS and ultimate tensile strength(UTS)of the alloy gradually increased with decreasing extrusion speed or extrusion temperature,while elongation to failure(EL)was gradually decreased.With the decrease of Zn/Ca ratio,the size and volume fraction of DRXed grain,and the volume fraction of precipitates in the Mg-Zn-Ca-Mn alloy was also decreased.The texture density of(0002)basal plane and(11-20)prismatic II plane for the alloy was gradually weakened.YS and UTS of the alloys gradually increased with the decrease of Zn/Ca ratio,while EL gradually decreased.The excellent YS?364.1 MPa,UTS?383.8 MPa and EL?6.1%were achieved in the ZXM-1.2 alloy extruded at 270?/0.01mm s^-1.The grain sizes of TiC_p/Mg-2.2Zn-1.8Ca-0.5Mn nanocomposite was significantly refined after extrusion,and the dynamical precipitated phase was Mg Zn₂.The size and volume fraction of DRXed grain and the size of the precipitates for the nanocomposite gradually decreased with decreasing extrusion speed or extrusion temperature,while the volume fraction of precipitates was slightly increased.YS and UTS of the nanocomposites gradually increased with decreasing extrusion speed and extrusion temperature,while EL decreased.With the decrease of Zn/Ca ratio,the size and volume fraction of DRXed grain,as well as the size and volume fraction of precipitates in the Ti C_p/Mg-Zn-Ca-Mn nanocomposite gradually decreased.As a result,YS and UTS of the nanocomposite were gradually increased,while EL gradually decreased.The highest tensile properties with YS?423.6 MPa,UTS?436.8 MPa and EL?2.4%were obtained in the Ti C_p/Mg-2.2Zn-1.8Ca-0.5Mn nanocomposite extruded at 270?/0.1mm s^-1.