中文摘要：

根据优化的激光工艺参数，利用激光冲击处理技术在AZ31B镁合金上制备出纳米结构表层，采用x射线衍射仪（XRD）和透射电镜（TEM）表征了AZ31B镁合金激光冲击处理后表面纳米层的微观结构，分析了纳米晶粒内微挛晶的成因，探讨了激光冲击处理诱导AZ31B镁合金晶粒细化的机理。晶粒细化机理归纳如下：在原始晶粒内，位错滑移导致位错缠结，应力集中诱发机械孪生；在亚晶粒和已经细化的晶粒内，继续形成位错缠结和位错胞；位错缠结转变成小角度取向差的亚晶界，细分粗大晶粒成亚晶粒；亚晶界演变成大角度晶界，最终形成等轴状、取向随机分布的纳米晶组织。

英文摘要：

According to the optimized laser parameters, a nanostructured surface layer was fabricated on an AZ31B magnesium alloy by Laser Shock Processing （LSP）. The microstructure of the nanocrystalline layer was characterized by means of X-ray diffraction （XRD） and transmission electron microscope （TEM）, and the formation reasons of micro-twins as well as a possible grain refinement mechanism were discussed. The grain refinement mechanism is proposed as following： in original grains, dislocation slipping leads to the formation of dislocation tanglings and stress concentration leads to deformation twinning; in the subgrains and refined grains, dislocation tanglings and dislocation cells are formed continuously; dislocation tanglings are transformed into subgrains boundary with low angle, which divides coarse grains into subgrains; subboundaries are gradually developed into grain boundary with high angle, and finally nano-scale grains with equiaxed shape and random orientations are formed.