Friction stir processing (FSP) was conducted on the hot-rolled Mg–3Gd–1Zn (GZ31) sheets for 1 and 4 passes to create a fine-grained structure. The superplastic behavior of the upper surface layer in the center of the stirred zone (SZ) was evaluated by the localized shear punch test (SPT) in the temperature range of 673–748 K. Microstructural analysis showed that FSP transformed the coarse-grained structure of the hot-rolled alloy with an average grain size of 49.5 μm to the fine and equiaxed grains of 4.6 and 2.7 μm after 1 and 4 passes, respectively. The maximum strain rate sensitivity (SRS) indices (m-values) of 0.23, 0.31, and 0.48 were achieved for the hot-rolled, 1 pass, and 4 passes FSPed conditions at 698 K, respectively. The corresponding activation energies were found to be 321, 212, and 119 kJ mol⁻¹ for these conditions. The shear stress-strain rate behavior of the alloy after 4 FSP passes conformed to regions I, II and III, which is characteristic of superplastic behavior. This was manifested by the high m-value of 0.48 and the activation energy of 119 kJ mol⁻¹, which are indicative of superplastic behavior, caused by the grain boundary sliding (GBS) of the fine equiaxed grains having a large fraction of high angle grain boundaries (HAGBs) of about 87%.

在热轧的Mg-3Gd-1Zn（GZ31）板材上进行了1和4道次的摩擦搅拌加工（FSP），以形成细晶粒的组织。在673–748 K的温度范围内，通过局部剪切冲压试验（SPT）评估了搅拌区中心（SZ）上表面层的超塑性行为。微观结构分析表明，FSP转变了粗晶粒结构在经过1次和4次通过后，平均晶粒度为49.5μm的热轧合金分别变为4.6和2.7μm的细晶粒和等轴晶粒。在698 K的热轧，1遍和4遍FSP条件下，最大应变速率敏感性（SRS）指数（m值）分别达到0.23、0.31和0.48。发现相应的活化能为321、212和119 kJ mol对于这些条件，为^-1。4 FSP通过后，合金的剪切应力-应变速率行为符合区域I，II和III，这是超塑性行为的特征。这表现为0.48的高m值和119 kJ mol ^-1的活化能，这是超塑性行为的指示，这是由高角度大比例的细等轴晶粒的晶界滑动（GBS）引起的晶界（HAGBs）约为87％。