铝合金搅拌摩擦焊材料流场非对称性的数值模拟研究

Numerical simulation of asymmetric materials flow field during friction stir welding of aluminum alloy

铝合金搅拌摩擦焊(FSW)过程中,搅拌头附近的材料在高温下发生剧烈的塑性流动。FSW过程中的材料流动直接关系到接头质量。由于运用试验直接观察手段研究固态金属的瞬态塑性流动十分困难,因此数值模拟是研究FSW过程中材料流动行为的重要手段。针对2024铝合金建立了基于计算流体力学(CFD)的材料流动模拟仿真模型,模拟得到了FSW过程中温度、塑性变形等物理量的三维分布。模拟结果与试验结果对比表明,温度场模拟结果与试验结果吻合良好;分析模拟结果发现,搅拌头附近材料应变速率并非对称分布。模拟结果表明,FSW过程中,材料在搅拌针前方分流,在搅拌针后方焊合,分流与焊合位置均位于前进侧;随着焊接速度的提高,焊合难度增大,从而使FSW过程中沟槽缺陷产生的倾向性增大。

Significant plastic flow occurred at high temperature during friction stir welding(FSW). The weld quality related to the material flow pattern closely during FSW process. Owing to the difficulties involved in experimental study on the transient material flow in FSW, numerical simulation became a powerful tool for investigating the material flow pattern during FSW. In this study, numerical simulation based on( CFD) was established to predict the material flow field during friction stir welding of aluminum alloy 2024. The predicted temperature agreed well with the experimental results. It was revealed that the material flow was non-symmetrical. Simulation results showed that the material separates in the front of the FSW pin and re-welds behind the pin. Both the separating and re-welding occurred on the advancing side. The difficulty of re-welding in FSW increased as the increasing of welding speed. As a result, the groove-like void was more likely to be formed.