铝镁双金属复合棒材反向等温挤压微观组织演化机理

Microstructures evolution of Mg-Al composite bar made by indirect isothermal co-extrusion process

针对铝镁双金属复合挤压工艺,探究棒材挤压过程中材料流动特性及微观组织演变规律。通过热模拟压缩试验得到不同温度下纯铝和镁合金的流变曲线,建立纯铝和AZ31镁合金的组织演化热力学模型并进行计算。研究发现双金属挤压过程中铝镁界面处材料流动速度相差较大,铝表层局部应变在进入模具工作带前达到临界值,摩擦热促使晶粒严重长大,产生粗晶:通过EBSD扫描结果可知交界面层从Al至Mg的相组成依次为Al、Al3Mg2、Al12Mg17、Mg,沿速度方向层状分布,与数值计算结果相符。通过与试验对比验证,晶粒尺寸计算的平均误差为17%,计算发现在温度满足热变形的条件下,材料应变对挤压复合材料的晶粒度影响较大,应变的增大促进再结晶致使晶粒尺寸增大。

Aiming at the aluminum and magnesium composite extrusion process,the material flow and microstructure evolution of the composites bar were investigated.The rheological curves of pure aluminum and magnesium alloy under different temperatures were obtained by thermal simulation compression test,and the evolution thermodynamic model of pure aluminum and AZ31 magnesium alloy were established and calculated.The study shows that the material flow velocity is quite different along the magnesium and aluminum interface.The local strain of aluminum surface reaches the critical value before entering the die working.The friction heat causes the grains to grow seriously,which brings coarse grain.Through EBSD scanning result,the phase composition in the boundary surface from the Al to Mg is in the order of Al,Al3 Mg2,Al12 Mg17,Mg,which are layered distributed along the velocity direction,and consistent with the results of numerical calculation.Compared with experimental verification,the average error of the grain size calculation is 17%.The calculation shows that under the condition of meeting the thermal deformation temperature,strain has a greater influence on the grain size of extruded composite materials,the recrystallization is promoted by the increase of strain,which causes the increase of grain size.