2A50铝合金挤压棒材尾端粗晶的产生原因及改善措施

Causes of coarse grains at the end of extruded bars of 2A50 Al alloy and corresponding improvement measures

利用偏振光、高倍组织和模拟等方式对2A50铝合金反挤压棒材尾部漏斗形缩尾、中心粗晶及正挤压表层粗晶环进行试验研究。结果表明,反挤压时尾端中心粗晶形成的原因是,挤压尾端死区的存在及流动金属受堵头的摩擦和冷却作用而使反挤压后期金属流动不均匀所致;正挤压产生的粗晶环,是由于外层金属变形程度比内层的大受到严重的剪切变形,积累的畸变能高,易发生再结晶并长大,且越靠近尾端越严重。同时,提出了改善缩尾、中心粗晶和粗晶环的措施。

Funnel-shaped contraction,central coarse grains in back-extrusion and coarsegrain rings at the surface layer in forward extrusion of 2A50 Al alloy are analyzed with the methods of polarized light,microstructure and simulation,etc. The results show that the causes of coarse grains formed at the tail center are the existence of dead zone at the extrusion end and also,the uneven flowing in the latter stage of back-extrusion caused by friction of container end and cooling effects. While the causes of coarse rings formed in the forward extrusion are the high distortion energy accumulated by greater deformation at the outer layer than that at the inner layer and occurrence of serious shearing deformation,as a result,the recrystallization is liable to happen and grow up which is more serious as closer to the end. At the same time,measures have been put forward to improve the conditions of contraction,central coarse grain and coarse-grain ring.