Y对AZ91镁合金半固态等温热处理组织的影响

Effect of Y on Microstructure of Semi-solid Isothermal Heat-treated AZ91 Magnesium Alloy

采用金相显微镜研究了Y含量、保温时间与保温温度对AZ91镁合金半固态组织演变的影响。结果表明,Y的加入阻碍了固相颗粒扩散,使Ostwald熟化减慢,促进了合金球状颗粒的形成;加入0.6%Y时镁合金半固态组织最为细小圆整。随着保温时间的延长,合金由大块状组织演变为均匀、圆整的球状组织;随着保温温度的升高,铸态合金中的初始树枝晶组织经过粗化、组织分离和球化演变成了半固态非树枝晶组织;然而,保温温度的过高与保温时间的过长,都会导致球状颗粒的粗化长大。AZ91稀土镁合金半固态成形所需的最佳工艺条件为加热温度565℃,保温时间30 min。

The effects of rare earth Y, holding time and holding temperature on microstructure evolution of AZ91 magnesium alloy in semi -solid state were investigated by using metallurgical microscope. The results show that yttrium contributes to refine the alloy＇s organization,which hinders proliferation of the particles of the solid phase, slows the Ostwald ripening and makes the microstructure of alloy grains more spheroidizing. Added 0.6% Y,the Semi -solid microstructure of magnesium alloy is the most fine and round. With the extension of holding time, the microstructure of alloy changed from large block into homogeneous spherical. During the increasing of holding temperature, the serious dendritic in the microstructure of the initial cast alloy turned into semi - solid non - dendritic and the evolution includes coarsening, microstructure separation and spheroidizing. When the holding temperature is much higher or the holding time is much longer, the spherical structure is susceptible to grow up. In addition,the best semi -solid structure for semi -solid -forming can be obtained at 570℃ with holding time 30 min.