挤压剪切与正挤压对AZ31镁合金塑性变形的影响

Effects of extrusion-shear and direct extrusion on the plastic deformation of AZ31 magnesium alloy

借鉴正挤压与多道次等通道挤压的特点提出了挤压(Extrusion)-剪切(Shear)复合挤压工艺(简称ES),制造了多副适合工业卧式挤压机的ES变形组合凹模,进行了ES挤压和普通挤压实验。构建了ES挤压和普通挤压的三维有限元热力耦合模型及数值模拟条件,对ES挤压过程的挤压力、累积应变演化进行了计算机模拟仿真。通过对坯料的应力状态进行了计算机模拟分析,发现ES挤压过程局部坯料受到四向压应力,ES挤压与普通正挤压相比可以显著提高镁合金变形过程的累积应变,因此可以更有效的细化晶粒。针对ES挤压和普通挤压棒料的不同位置进行了微观组织观察,发现在挤压温度为370℃、挤压比为12时ES挤压可以有效的细化晶粒,不仅可以细化棒材表层晶粒,心部也得到了细化。

A new method for magnesium alloy composite extrusion was presented which combines the traditional extrusion and two shears(ES) and derivate from characteristics of extrusion and multi pass equal channel.Some ES combination dies used in industrial horizontal extruder were designed and manufactured,extrusion experiments for ES extrusion and direct extrusion were done respectively.The same extrusion experiments were done with identical conditions as simulation conditions.Three-dimensional(3D) finite element models(FEM) and simulation conditions were established according to ES process and performed by using commercial software DEFORMTM-3D,The ES extrusion process,extrusion pressure and the cumulative strain evolution were simulated by computer simulation.The analysis results for stress state of the billets show that ES billet extrusion process by the four direction compressive stress,and billets are exerted continuous shear stress after the direct extrusion,and ES extrusion can significantly improve the cumulative strain of plastic deformation for magnesium alloys compared with which caused by direct extrusion.The analysis show that ES process can refine grains of magnesium alloys effectively.Microstructure observations from the different positions of magnesium rod extruded by ES extrusion and direct extrusion were done.1-2 μm grain size of recrystallization grains can be obtained with extrusion ratio 12 and extrusion temperature 370 ℃.Grains of magnesium alloy rods including the grains of rod surface and the center can be refined by ES extrusion effectively.