Elemental Research on Die Design for Achieving High Quality Products in Hot Extrusion

热挤压模具设计要考虑模具本身的弹性变形，实现无缺陷的良好制品，就需要进行详细、真实的应力分析。在优化挤压工艺和模具设计时，还需要对跳动方向进行力学解释，因为跳动方向与某些铝合金热挤压过程中的产品横截面变形和周边再结晶变形密切相关，从而导致阳极氧化后产生条纹。本文对Al-Mg-Si(6063)铝合金进行了单轴压缩试验、对称模具和非对称模具的平面应变热挤压实验，并进行了数值分析。1)考虑了热挤压变形区有效应变率、有效应变和温度的复杂分布，引入了作者提出的加工硬化速率方程来预测塑性加工能引起的有效应力和温升的分布。2)。挤出产品的跳动方向可能与u=0线与挤出方向的夹角有关。(速度分量u指向挤出方向的法线方向。)U=0线的角度既可由模具结构控制，也可由死区控制。3)。当有效应变epsilon小于1.55或有效应变梯度小于0.44epsilon时，热挤压制品不会产生周边再结晶组织。这些值在473ﾟ℃时分别为1.55和0.44，并随温度升高而变小。4)在表面光滑、导热系数低的陶瓷模具挤压过程中，观察到了含有薄层死金属区的金属流动规律。

Die design considering the elastic deformation of die itself and achieving the sound product without defect in hot extrusion requires detailed and realistic stress analysis. Mechanistic interpretation of run-out direction, which is closely connected with distortion of the cross section of the product and that of peripheral recrystallization in hot extrusion of some aluminum alloys, which causes streaks after anodizing, are also required to optimize the extrusion process and die design. In the present investigation, some uniaxial compressive testings of Al-Mg-Si (6063) aluminum alloy, plane strain hot extrusion experiments of the same alloy using the symmetric and non-symmetric dies and numerical analyses concerning with the above subjects were performed. Those results are summarized below.1) The work-hardening rate equations proposed by the investigator previously were introduced to predict the distributions of effective stress and temperature rise due to plastic working energy with taking into account the complex distributions of effective strain-rate, effective strain and temperature in the deformation zone in hot extrusion. 2). Run-out direction of the extruded product could be related to the angle between the u=0 line and the extrusion direction. (Velocity component, u, is directed to normal direction to the extrusion direction.) The angle of u=0 line can be controlled by both die configuration and dead metal zone. 3). The peripheral recrystallized grain structure is not generated in hot extruded product when the effective strain, epsilon, is less than 1.55 or the effective strain gradient is less than 0.44epsilon is satisfied. Those values, 1.55 and 0.44, are obtained at 473^ﾟC and become smaller at higher temperature. 4) The metal flow patterns involving thin dead metal zones were observed in extrusion using ceramic dies having smooth surface and low heat conductivity.