AZ21镁合金降温多向压缩过程中的组织和微观织构演化

EVOLUTIONS OF MICROSTRUCTURE AND MICROTEXTURE IN AZ21 Mg ALLOY DURING MULTI-DIRECTIONAL FORGING UNDER DECREASING TEMPERATURE CONDITIONS

对AZ21镁合金进行了降温多向压缩变形,利用OM及SEM/EBSD技术观察和分析了其显微组织和微观织构的演化.结果表明,随着变形道次的增加,晶粒尺寸迅速减小,经4道次的变形晶粒可细化至0.8μm.高温变形时生成的相互交叉的扭折带可将原始晶粒有效地分割而细化.673 K第1道次变形至ε=1.2时,几乎所有的晶粒都发生了90°的转动,基面由变形前平行于压缩方向转至与压缩方向垂直,基面织构强度先减小后增大;第2道次变形时,织构变化与第1道次基本一样,表现为与变形温度无关,仅取决于变形程度.第2道次变形后织构强度低于第1道次,变形道次的增加可以弱化织构.

Grain refinement and texture evolution of a magnesium alloy AZ21 were investigated during multi-directional forging under decreasing temperature from 673 K to 433 K.Dynamic recrys- tallization（DRX） and texture development were studied at 673 K by OM and SEM/EBSD techniques. The flow curves show rapid hardening accompanied by a stress peak at relatively low strains,followed by strain softening and then a steady state flow stress at high strains.Kink bands with low to medium angle misorientations are evolved at corrugated grain boundaries and also frequently in grain interiors at low strains.Some of them intersect with each other,leading to the fragmentation of original grains. The alignment of the basal planes initially parallel to the compression axis rotated gradually by com- pression at 673 K and approached an orientation perpendicular to the compression axis at e=1.2.The relative intensity of texture decreases rapidly with increasing strain to ？=0.4 and goes up later.A sim- ilar trend of texture evolution is recognized for the second pass,implying slightly effect of temperature but rather of strain.It is also concluded that increasing the deformation passes can lead to a decrease in texture intensity.