Optimization of Dissimilar Joining Process for Lap Joint of Mg Alloys by using Friction Spot Joining based on Frictional Stirring Phenomenon

本研究旨在揭示镁合金与镀锌钢板异种搭接摩擦点连接工艺的连接机理，研究摩擦点连接工艺参数与异种搭接接头力学性能的关系，建立异种摩擦点连接工艺优化方法，并对该连接工艺进行塑性流动有限元分析。首先，研究了2 mm厚AZ 31 B、AM 60和不燃AMC 602镁合金薄板摩擦点焊的焊接性。在相同的连接条件下，工具伸出（探针）高度为2.4 mm，工具旋转速度为1750 min-1，工具插入下压力为9.8 kN，AZ 31 B合金和AM 60合金的搭接接头的最大拉伸剪切强度分别为4.2 kN和3.3 kN<-1>。然后，研究了刀具转速对AM 60拉伸剪切强度的影响。最大拉伸剪切强度为4.3 kN的工具旋转s 关于我们 对于<-1>工具旋转速度5000 min-1，为2.0 kN<-1>。由于AMC 602合金具有比AM 60更高的塑性变形能力，在相同的FSJ条件下，AZ 31 B合金的最大拉伸剪切强度与AMC 602合金相同。接着，对2 mm厚的AZ 31 B与0.8mm厚的冷轧钢板（SPCC）或0.8mm厚的锌合金镀层钢板（GA）进行摩擦点焊。我们获得了AZ 31 B-SPCC的搭接接头，探针高度为1.9 mm，工具转速为1500 min^-1，工具插入下压力为9.8 kN。同时，采用二维轴对称模型，利用探针长度分别为1.9mm、2.4mm和2.9mm的工具，对AZ 31 B-GA搭接接头的塑性变形行为进行了分析。随着探针长度的增加，计算速度和精度下降。此外，有限元网格需要频繁地重新生成以保证收敛，轴对称模型不能处理周向应变。因此，我们意识到这种方法是不够的，摩擦点连接过程的优化方法。为了获得更高的异种搭接接头的拉伸剪切强度，我们将需要优化的工具形状和连接参数在未来的日子。此外，我们将需要三维模型来优化摩擦点连接过程。少

The purpose of this research is to reveal the joining mechanism of friction spot joining process in the dissimilar lap joint between magnesium alloy and zinc coated steel, to investigate relation between the process parameters of friction spot joining and mechanical properties of dissimilar lap joint, moreover, to establish the optimization method of dissimilar friction spot joining process aided by plastic flow FE analysis of this joining process.First of all, we investigated the weldability of friction spot joint of 2 mm thick AZ31B, AM60, and noncombustible AMC602 magnesium alloys sheets. Maximum tensile shear strength of lap joint was 4.2kN for AZ31B alloy and 3.3 kN for AM60 alloy in the same joining conditions of tool projection (probe) height 2.4 mm, tool rotational speed 1750 min^<-1>, and tool plunge downforce 9.8 kN. Then, the effect of tool rotational speed on the tensile shear strength of AM60 was surveyed. Maximum tensile shear strength was 4.3 kN for the tool rotational s … More peed 3000 min^<-1> and 2.0 kN for the tool rotational speed 5000 min^<-1>. As the AMC602 alloy has higher plastic deformability than AM60, the maximum tensile shear strength was the same as that of AZ31B for the same FSJ condition. Next, we performed the friction spot joining of 2 mm thick AZ31B and 0.8 mm thick cold rolled steel sheet (SPCC) or 0.8 mm thick zinc alloy coated steel sheet (GA). We obtained the lap joint of AZ31B-SPCC for the probe height 1.9 mm, tool rotational speed 1500 min^-1, and tool plunge downforce 9.8 kN. However, we have not obtained the lap joint of AZ31B-GA for the same joining condition.At the same time,we analyzed the behavior of plastic deformation for the lap joint by using tool, which has three kind of probe length; 1.9 mm, 2.4 mm, and 2.9 mm. This analysis used the 2-dimensional axi-symmetric model. Computational speed and accuracy decreased according to the increasing of probe length. Moreover, frequent re-creation in FE mesh must be need for convergent result and axi-symmetric model was not treat strain in circumferential direction. Therefore, we realized that this approach was inadequate for optimization method of friction spot joining process. In order to achieve the higher tensile shear strength of dissimilar lap joint, we will need the optimized tool shape and joining parameters in the days ahead. Moreover, we will need the 3-dimensional model to optimize friction spot joining process. Less