Composition Design And Strengthening And Room Temperature Mechanical Properties Of Mg–Zn–Ca System Magnesium Alloys With Low Alloy Content

Magnesium alloys,as the lightest engineering structural metal materials,have a lot of advantages,i.e.high specific strength and specific stiffness along with good damping capacity,receiving extensive attention in areas of automobile,aerospace and communication industry.Compared with casting Mg alloys,wrought ones have better mechanical properties.However,wrought Mg alloys usually possess an intensive basal texture which results in poor room-temperature formability,hindering the further application of them severely.In this work,based on Mg-Zn-Ca alloys with low alloying contents,the Magnesium alloy sheets with weak textures,high strength and ductility are developed.The effect of Zn content on the microstructure,texture and mechanical property of rolling Mg-xZn-0.2Ca(x=0.5,1.0,1.5,2.0 wt.%)alloys is investigated.Besides,the roles of Zn and Ca on the microstructure,texture and mechanical property of Mg are also studied.The main conclusions are as follows.(1)As the Zn content increases,the number of secondary phases in the alloys raises,increasing the stored energy in as-rolled alloys which enhances the recrystallization driving force and thus promotes the static recrystallization.Meanwhile,the enhanced solute dragging effect and the pinning effect of nanometric secondary phases impede the preferential growth of recrystallized grains,reducing the texture intensity of Mg-xZn-0.2Ca alloys gradually.(2)As the Zn content increases,the strength and ductility of Mg-xZn-0.2Ca alloys raise gradually.The enhancement of strength is attributed to the enhanced precipitation strengthening,solution strengthening and greater work hardening rates,while that of ductility is due to the improvement of uniform elongation and post-uniform elongation.Nevertheless,when Zn content reaches 2.0 wt.%,the distribution of secondary phases appears to be ribbonlike,resulting in low ductility.Therefore,Mg-1.5Zn-0.2Ca alloy possesses excellent mechanical property,i.e.ultimate tensile strength of?274 MPa and fracture elongation of?27%.(3)Both individual addition and co-addition of Zn and Ca can induce grain refinement which is attributed to solute dragging and precipitate pining.In alloys containing Zn,grain growth,particularly preferential grain growth is hindered by solute dragging of Zn,resulting in grain refinement.While in alloys containing Ca,grain growth is hindered by strong precipitates pinning and solute dragging of few Ca atoms,leading to effective grain refinement.In terms of co-addition of Zn and Ca,the annealed Mg-l.5Zn-0.2Ca alloy possesses fine and uniform grains which results from the improved precipitate pinning and solute dragging.(4)Both individual addition and co-addition of Zn and Ca can reduce the texture intensity,which is attributed to non-basal slip,solute dragging and precipitate pinning.The co-addition of Zn and Ca promotes non-basal slip the most and induce the most fine precipitates and co-segregation of Zn and Ca which impedes preferential growth of recrystallized grains,leading to the weakest texture in the annealed Mg-1.5Zn-0.2Ca alloy.(5)Both individual addition and co-addition of Zn and Ca can enhance the tensile yield strength of alloys,which is attributed to solute strengthening and grain-boundary strengthening.Besides,it can effectively reduce CRSSnon-basal/CRSSbasal,activate non-basal slip,thus enhance ductility of alloys.While in terms of co-addition of Zn and Ca,the enhanced grain-boundary strengthening and precipitation strengthening,more residual dislocation and more active non-basal slip,give the annealed Mg-1.5Zn-0.2Ca alloy excellent tensile yield strength and ductility.(6)Both individual addition and co-addition of Zn and Ca can affect the work hardening behaviors of alloys,which is mainly attributed to dislocation storing capacity of them.When adding 1.5 wt.%Zn to pure Mg,compared with solute atoms,grain refinement affects the dislocation storing capacity of alloys more,resulting in lower work hardening capacity.While in terms of alloys containing Ca,the grain refinement reduces dislocation storing capacity of alloys significantly and thus results in low work hardening capacity.Note that in the Mg-1.5Zn-0.2Ca alloy,there are more fine precipitates which promote the production and accumulation of dislocation,giving it higher work hardening capacity than Mg-0.2Ca alloy.