SIMA法制备AM60B镁合金球晶组织及触变成形(英文)

通过应变诱导熔化激活法制备半固态AM60B镁合金,并研究其组织演变。分别采用往复挤压镦粗(CEC法)和传统压缩预成形铸态AM60B镁合金,并在半固态区间部分重熔和触变成形。结果表明,CEC态镁合金的粗晶组织消失,出现细小晶粒组织,但是压缩态合金的粗晶和再结晶晶粒共存。在局部重熔过程中,CEC态合金获得理想的细晶组织,完全球化的晶粒被液相均匀包裹。在压缩态合金中,多边形晶粒在一定程度上球化,但是之前不规则的形状仍然明显存在。CEC加上二次重熔触变成形的AM60B镁合金,其力学性能优于压缩态加上二次重熔触变成形的镁合金的。     

Nd对Mg-2Ca合金组织和性能的影响

以Mg-2Ca-xNd三元合金为主要研究对象,运用金相分析(OM)、扫描电镜分析(SEM)、能谱分析(EDS)、X射线衍射分析(XRD)及万能拉伸试验机等多种分析和测试手段,系统研究了稀土元素Nd含量对Mg-2Ca-xNd三元合金的显微组织和力学性能的影响.结果表明,随着Nd含量的增加,晶粒变得细小,当Nd含量超过2%时,晶粒又开始变得粗大,并且晶界析出相明显增多,晶内析出大量针状Mg-Nd金属间相.Mg-2Ca-xNd合金的抗拉强度先升高后降低,合金的塑性降低.Mg-2Ca-xNd合金的硬度随着Nd含量的增加而增加.     

Grain coarsening in semi-solid state and tensile mechanical properties of thixoformed AZ91D-RE

For thixoforming to be possible,the microstructure of the starting material must be non-dendritic,which can be obtained by the strain induced melt activation(SIMA)route.Based on the SIMA route,as-cast AZ91D alloy with the addition of yttrium was deformed by cyclic closed-die forging(CCDF).Microstructure evolution of CCDF formed AZ91D-RE alloy during partial remelting were investigated.Furthermore,the mechanical properties of thixoformed AZ91D-RE magnesium alloy components were also studied.The results showed that prolonged holding time resulted in grain coarsening and the improvement in degree of spheroidization.The coarsening behaviour of solid grains in the semi-solid state obeyed Ostwald ripening mechanism.The coarsening rate constant of CCDF formed AZ91D-RE during partial remelting was 324 um3/s at 550℃.The value of yield strength,ultimate tensile strength and elongation to fracture of four-pass CCDF formed AZ91D-RE magnesium alloy were 214.9,290.5 MPa and 14%,respectively.Then the four-pass CCDF formed alloys were used for thixoforming.After holding at 550℃ for 5 min,the values of yield strength,ultimate tensile strength and elongation to fracture of thixoformed component were 189.6 MPa,274.6 MPa and 12%,respectively.However,prolonged holding time led to remarkable decrease in mechanical properties of thixoformed components.