Study On Microstructure And Mechanical Properties Of Micro-alloyed Mg-Zn Alloy With High Formability

As the lightest metal structural material,magnesium(Mg)alloys with the advantages of high specific strength and specific stiffness,good vibration damping characteristic and electromagnetic shielding property,have a huge potential application prospect in aerospace,automobile,3C and other industries.Generally speaking,Mg alloys have insufficient slip systems that can be activated at room temperature,and wrought Mg alloy usually exhibit strong basal texture,which leads to serious mechanical properties anisotropy and poor forming properties at room temperature.In this paper,Mg alloys with high formability at room temperature were prepared using multi-element micro-alloying.The effects of Zn content on microstructure,texture,and mechanical properties of Mg-x Zn-0.2Ca-0.2Ce alloys were studied.The microstructure,texture,and mechanical properties evolution of Mg-1.5 Zn Mg alloy with 0.2 wt.% Ca,Ce,and Mn addition were also investigated.Also,the microstructure and texture evolution of Mg-1.5Zn-0.2Ca-0.2Ce alloy were studied under different rolling reduction and annealing conditions.The main research contents and experimental results are as follows:(1)Mg-x Zn-0.2Ca-0.2Ce(x = 0.5,1.0,1.5,2.0 wt.%)Mg alloy exhibited bimodal texture with basal poles inclined from ND to ED after hot extrusion.With the increase of Zn content,the texture strength decreased,and the basal texture were deflected to the TD direction,gradually;the activity of the non-basal slip systems gradually increased,and the plasticity of Mg alloy increased.When the Zn content reached 2.0 wt.%,the precipitation strengthening of the second phase intensified,and the plasticity deteriorated.(2)After hot rolling and annealing,Mg-x Zn-0.2Ca-0.2Ce alloys exhibited bimodal texture with basal poles inclined from ND to TD.With the increase of Zn content,the basal texture component deflected along the TD direction gradually increased,while the texture component deflected along the RD gradually decreased.With the increase of Zn content,the yield strength of the Mg-x Zn-0.2Ca-0.2Ce alloys did not increase,but the yield strength along the TD direction gradually decreased.The ZXE1500 alloy achieved a maximum elongation of ? 42.4%,and its Erichsen value was 7.7 mm.(3)The dislocation plugging rates of Mg-0.5Zn-0.2Ca-0.2Ce and Mg-1.5Zn-0.2Ca-0.2Ce Mg alloys were independent of the load direction at the initial stage of uniaxial tensile deformation.The bimodal texture along the TD direction made it easy to dynamically recover in the RD direction.The Erichsen cupping test sample was under non-iso-biaxial tensile stress in the area near the crack,and the radial strain was much larger than the circumferential strain,making the texture evolution of this area similar to the sample under uniaxial tension.(4)Mg-1.5Zn-0.2Ca,Mg-1.5Zn-0.2Ce,Mg-1.5Zn-0.2Ca-0.2Ce and Mg-1.5Zn-0.2Ca-0.2Ce-0.2Mn alloys were performed hot extrusion,and all of them formed the bimodal texture along the ED direction,and then the bimodal texture became along the TD direction after the hot rolling process and annealing treatment.Adding Ce alone had better texture weakening effect on Mg-1.5Zn alloy than adding Ca alone.The ZXEM15000 alloy had the strongest bimodal basal texture,but due to more alloying elements,the strength and plasticity of the alloy are weakened.(5)The Mg-1.5Zn-0.2Ca-0.2Ce-0.2Mn alloy was rolled at 400 ?,with the increase of reduction,the proportion of tensile twins gradually decreased,while the proportion of compression twins and secondary twins gradually increased.After hot rolling,ZXE1500 alloy still exhibited bimodal texture with basal poles inclined from ND to RD,while the degree of divergence of the basal poles in the RD direction gradually decreased;the texture strength first increased and then decreased with the increase of deformation.The reason for the weakened texture was recovery and recrystallization.After annealing,the bimodal basal texture of the ZXE1500 alloy gradually became an elliptical texture with the major axis in the TD direction.When the rolling reduction was more than 38%,the texture strength did not change anymore.(6)The ZXE1500 alloy was rolled at room temperature,with the increase of rolling reduction,the divergence of the bimodal basal texture along the RD direction gradually decreased,and the texture strength gradually increased.The tensile twins produced during the rolling process were mainly “abnormal twins” with negative SF.The “abnormal twins” are mainly due to the local strain coordination.