Al/Mg异种合金搅拌摩擦连接材料流动可视化和数值模拟研究

在搅拌摩擦焊接（FSW）过程中，连接区金属材料的流动模式与接头组织的形成密切相关，对接头力学性能有着至关重要的影响。本文采用切片法研究了搅拌摩擦焊接接头的材料流动。通过对接头的三维重建，实现了流动材料的可视化，讨论了接头材料的流动模式和缺陷产生的原因。基于计算流体力学(CFD)和多相流理论，本文建立了FSW过程中铝合金/镁合金材料流动的三维数学模型。通过在数值模型中加入分布的示踪粒子，对不同连接参数下的材料流动模式进行分析和预测。结果表明：接头上部材料流动强烈，材料整体向前进侧迁移，接头中部前进侧镁合金向接头前部迁移，暂时形成的空腔由后退侧迁移来的铝合金填充。当不恰当的工艺参数使材料流动不充分时，未被完全填充的空腔会形成孔洞缺陷。接头整体材料主要以层流为主。在满足材料流动热输入需要时，接头材料的流动模式基本不发生改变，在高转速过热条件下，材料的迁移距离和混合模式会发生改变，两材料围绕搅拌头以层流模式多次越过对接线并充分混合，同时在后退侧产生紊流现象。

Study on visualization and simulation of the material flow in Al/Mg dissimilar friction stir joining

The flow pattern of materials is closely related to the formation of joint structure, has a crucial influence on the mechanical properties of joints for friction stir welding. The material flow of the joint was studied by slicing method which was adopted to observe different layer for dissimilar friction stir butt welding. The visualization of the flow material was accomplished by 3D reconstruction of the joint, which shows the flow pattern of the joint and the cause of the defect. The three-dimensional mathematical model of the flow of Al/Mg materials in FSW process is established based on computational fluid dynamics (CFD) and multiphase flow theory in this paper. The material flow patterns are analysed and predicted under different welding parameters by the distribution of tracing particles added in numerical models. The study reveals that the flow of material in the upper part of the joint is strong, the material moves to the front of tool as a whole. The magnesium alloy of the middle part in the advancing side of the joint moves forward to the front of the tool, and the temporarily cavity is filled with aluminum alloy from the retreating side. The cavity which is not completely filled will form a hole defect when the material flow is not enough due to improper process parameters. The whole joint material is mainly laminar flow. The flow mode of joint material basically does not change when the heat input is satisfied. The transfer distance and mixing mode of material will change under the condition of high rotation speed or overheat. The two materials cross the butt line for many times in mode of laminar flow around the tool and mix fully when the turbulence occurs at the retreating side.