AZ61镁合金薄板超塑性变形特征的SEM研究

利用扫描电镜(SEM)和超塑性拉伸实验对一次热挤压加工成型的AZ61镁合金薄板(晶粒尺寸～12μm)超塑性变形特征进行了研究.结果显示,在最佳的变形温度(623K)和应变速率(1×10-4s-1)条件下,可获得的最大的超塑性形变量为920%.在523～673 K实验温度和1×10-2～1×10-5s-1应变速率范围内,材料的应变速率敏感指数(m值)随实验温度升高和应变速率的降低而增加.较高的m值(0.42～0.46)对应于晶界滑动机制(GBS),而较低的m值(0.22～0.25)则对应于位错滑移机制.变形温度和应变速率是影响超塑性变形量和变量机制的主要因素.

SEM Investigation on Superplastic Deformation in Mg-AZ61 Alloy Sheet

The superplastic behavior of the AZ61 magnesium alloy sheet, processed by one-step hot-extrusion and possessing medium grain sizes～12 μm, has been investigated over the temperature range of 523～673 K.The highest superplastic elongation of 920% was obtained at 623 K and 1×10-4 s-1. In the lower and higher strain rate regimes, with apparent m-values～0.45 and～0.25, respectively, GBS and dislocation creep appeared to dominate the deformation process, consistent with the SEM examination. The deformation mechanism transited form dislocation process to grain boundary sliding with increasing strain rate and temperature that corresponds to m-values.The strain rate and temperature are important two factors on superplastic deformation.