Research On Roll-bonding Processes,microstructures And Properties Of Mg-Sn-Y/Al Composite Plates

Mg/Al composite plates,which not only possess the characteristics of low density,light weight,good damping performance and high specific strength of magnesium alloy,but also the advantages of corrosion resistance,low cost and high plasticity of aluminum alloy,are widely used in automotive,electronic equipment,3C and aerospace fields.However,the traditional magnesium alloy(AZ alloys and ZK alloys)owns the poor creep resistance at high temperature and low plasticity at room temperature,and the traditional method of rolling Mg/Al composite plates exist problems such as residual stress in plates and inconsistent coordination of deformation of elemental metals.However,the Mg-Sn base alloy has better high-temperature strength and creep resistance,and the addition of Y elements can improve the tensile asymmetry of the magnesium alloy,so that MgSn-Y alloy is a better choice as a base material.Thus,in this work,the actual constituents of Mg-0.5Sn-0.45 Y magnesium alloy plates were selected as basal plates and Al6061 plates were selected as cover plates,and Mg/Al composite plates were successfully prepared by differential temperature + asynchronous rolling(DTAR)at 40%-60% reductions,which were contrasted by Mg/Al composite plates rolled on isothermal + synchronous rolling(ISR)under the same range of reductions.The microstructure,mechanical properties and residual stress evolution of the Mg/Al composite plates rolled by two processes were studied in the same range of reductions.The rolled Mg/Al composite plates with better performance were annealed to study the evolution of microstructure and mechanical properties of Mg/Al composite plates under different annealing conditions.The results of the study showed that:(1)Both ISR and DTAR process made the Mg layer in Mg/Al composite plates grain refined,texture intensity and Schmidt factor decreased.Compared with ISR,due to the frictional shear effect in DTAR made the Mg layer in plates under this process continuously absorbed dislocations during the rolling process,and the ratio of low angle grain boundaries and Kernel average misorientation were lower,so that the grain refinement was higher,but the Schmidt factor was smaller and the texture intensity was higher.(2)Both ISR and DTAR made the bonding strength of Mg/Al composite plates increase with the increasing reductions.Due to the higher grain refinement of Mg layer and the shear force in the composite area,the Mg/Al composite plates rolled by DTAR had a higher bonding strength compared to that of plates rolled by ISR.Besides,the ultimate tensile strength(UTS)and yield strength(YS)of the Mg/Al composite plates in processes of ISR and DTAR increased with the increase of reductions,while the fracture elongation(FE)showed the opposite trend.Due to the smaller grain size of Mg layer,higher bond strength and hardness of composite plates under DTAR,the composite plate with higher tensile strength and yield strength was rolled by DTAR,but its elongation was lower.(3)The residual stress along rolling direction of the Mg/Al composite plates obtained by ISR and DTAR tended to increase and then decrease with the increasing reductions.Compared with ISR,the residual stress of Mg/Al composite plates rolled by DTAR were lower.(4)The UTS and YS of Mg/Al composite plates decreased with the increasing annealing temperature or annealing time,while the plasticity was improved after annealing.The FE of the composite plate reached the optimum under the annealing condition of 300℃-2h,the annealing treatment under this annealing condition promoted to activate the basal slip system of Mg layer,so that the Schmid factor was elevated,which played a positive role in enhancing the plasticity of overall plate.The texture intensity increased compared with that before annealing,and the corresponding grain boundary misorientation showed a discontinuous distribution.Meanwhile,the thickness of the interfacial diffusion layer increased with the increasing annealing temperature and time.It was helpful to improve the bonding strength when the plates were annealed at 200℃ for 1h-2h,which was mainly related to the formation of a strong solid diffusion layer at the interface.