焊接速度对铝合金搅拌摩擦焊接头性能的影响

李落星 张鹏 易林峰 吴时盛 周巧英

摘   要：以厚度3 mm的6061-T6铝合金板材搅拌摩擦焊对接接头为研究对象，建立热力耦合有限元模型，准确模拟了焊接过程的温度场分布及演变规律，采用光学显微观察、电子背散射衍射、显微硬度测量以及拉伸试验等表征方法，研究了焊接速度对焊接接头成形特性、显微组织和力学性能的影响机理. 结果表明：接头焊核区在焊接过程中经历了完全动态再结晶，形成细小等轴晶;后退侧热影响区经历了动态回复，晶粒显著长大，晶界强化作用弱于焊核区晶粒;当焊接速度为300～800 mm/min时，接头焊缝成形良好，拉伸断裂均在焊缝后退侧热影响区，在焊接过程中受温度（400～480 ℃）影响显著，析出强化相溶解导致力学性能明显降低，在此焊接速度范围内，随速度的提高，接头强度增加，最高强度系数为80.86%（800 mm/min）;当焊接速度进一步增加至1 200 mm/min时，接头的焊接成形性变差，焊核区出现未焊合和隧道缺陷，接头拉伸试验时在焊核区发生断裂.

关键词：搅拌摩擦焊;铝合金;力学性能;焊接速度

中图分类号：TG453                              文献标志碼：A

Effect of Welding Speed on Properties of Friction

Stir Welded Joint of Aluminum Alloy

LI Luoxing1†，ZHANG Peng1，YI Lingfeng2，WU Shisheng2，ZHOU Qiaoying1

（1. State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body，Hunan University，Changsha 410082，China;

2. AECC South Industry Company Limited，Zhuzhou 412002，China）

Abstract：Taking the friction stir welded joints of 3 mm thickness 6061-T6 aluminum alloy plate as the research object， a thermal mechanical coupling finite element model was established to accurately simulate the temperature filed distribution and evolution law of the welding process. The influence of different welding speeds on forming characteristics， microstructure and mechanical properties of the joints was studied by using optical microscopy， electron backscatter diffraction， microhardness measurement and tensile test. The results show that a completely dynamic recrystallization process occurs in the nugget zone during the welding process， which generates fine equiaxed grains， whereas the heat-affected zone （HAZ） on the retreating side undergoes dynamic recovery， resulting in the obvious grain growth. It is also found that the strengthening effect of grain boundary in the HAZ is weaker than that in the nugget zone. The joints are well-welded when the welding speed is 300～800 mm/min， and the fracture occurring in the HAZ of the retreating side could be mainly attributed to the temperature（400～480 ℃），dissolution of the precipitation phase leads to a significant reduction in the mechanical properties，and in this welding speed range，the joint strength increases with the increase of welding speed，and the highest strength factor is 80.86%（800 mm/min）. As the welding speed is further increased to 1 200 mm/min， the weld formability of the joint would deteriorate significantly due to the insufficient heat input and thermo-plasticity. Besides， the un-welded and tunnel defects in the weld nugget lead to the occurrence of the fracture in the nugget zone during tensile test.

Key words：friction stir welding;aluminum alloys;mechanical properties;weld speed

汽车轻量化是实现节能减排的重要途径，主要包括结构轻量化和材料轻量化. 铝合金是理想的轻量化材料，具有密度低、比强度高、耐腐蚀等特点，已广泛应用于航空航天、轨道交通、汽车工业等领域. 其中，6系铝合金的力学性能可通过热处理灵活调控，应用广泛，但其连接工艺仍存在一定的挑战. 传统铝合金焊接技术存在诸多不足，易出……