转速对6061铝合金搅拌摩擦搭接焊接头组织和力学性能的影响

目的 研究不同转速条件下6061铝合金搅拌摩擦搭接焊接头组织和力学性能的变化规律，为工程实践应用提供参考。方法 在不同旋转速度（800、1 200、1 500 r/min）下对4 mm厚的6061铝合金进行搅拌摩擦搭接焊实验，固定进给速度和轴肩下压量，研究搅拌头转速对接头宏观组织、微观组织和力学性能的影响。结果 所有接头均没有出现明显缺陷，当转速为1 500 r/min时，搅拌区晶粒尺寸细化明显，最大失效载荷达到母材的75%，上板和下板的硬度曲线都呈“W”形；当转速为800 r/min和1 200 r/min时，下板硬度曲线呈“V”形。随着转速的增大，有效搭接宽度逐渐增大，接头的平均拉剪强度也在增大，所有接头都在前进侧断裂，断裂形式均为拉伸断裂。结论 转速的提升增加了焊接热输入量和机械搅拌作用，促进了有效搭接宽度的增大和晶粒尺寸的细化，但未能改变钩状缺陷的形成及延伸方向。当转速为1500r/min时，热输入量较大，搅拌区范围相对较大，下板存在更大面积的搅拌区，其硬度规律与上板的相似。所有接头均为拉伸断裂，断裂位置在热影响区附近，说明搭接接头连接良好。

Effect of Rotational Speed on Joint Microstructure and Mechanical Properties of 6061 Aluminum Alloy Friction Stir Lap Weld Joint

The work aims to study the changes of joint structure and mechanical properties of 6061 aluminum alloy friction stir lap joint welded under different speed conditions, to provide a reference for the application of engineering practice. Friction stir lap welding experiments were performed on 4 mm thick 6061 aluminum alloy at different rotational speeds, fixed feed speed and the plunge depth of the shoulder, and three groups of parameters 800, 1 200, and 1 500 r/min were selected for rotational speed, to study the effects of stirring head rotational speed on the macrostructure, microstructure and mechanical properties of the joint. No obvious defects appeared in all joints. When the rotational speed was 1 500 r/min, the grain size refinement in the stirring zone was obvious, the maximum failure load reached 75% of the base metal, and the hardness curves of both the upper and lower plates were in the shape of "W"; however, the hardness curve of the lower plate was in the shape of "V" at 800 r/min and 1 200 r/min. With the increase of the rotational speed, the effective lap width gradually increased, the average tensile shear strength of the joint also increased, all joints were fractured from the advancing side, and the fracture form was tensile fracture. The increase of the rotational speed increases the welding heat input and mechanical stirring effect, which promotes the increase of the effective lap width and the refinement of grain size, but fails to change the formation and extension direction of hook defects. The higher heat input at 1 500 r/min results in a relatively larger range of the stirring zone, and the presence of a larger stirring zone in the lower plate makes the hardness law similar to that of the upper plate. All joints are subject to tensile fracture, and the fracture location is near the heat-affected zone, indicating that the lap joints are well connected.