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采用搅拌摩擦焊方法(FSW)对6 mm厚的6061-T4铝合金板材进行对接,焊后利用光学显微镜(OM)和扫描电镜(SEM)分析、对比了焊接接头和母材的显微组织和断口形貌特征,并测试了其室温拉伸性能和显微硬度。实验结果表明:选择了适合于6061-T4铝合金板材搅拌摩擦焊的工艺参数:焊接时搅拌头旋转速度为1200 r.min-1,工件的进给速度为300 mm.min-1,在此参数下获得了与母材等强度、韧性接近于母材的焊接接头,为此种合金应用于汽车关键零部件提供了可靠的工艺方法。FSW板材接头焊核区的组织和性能明显优于其他区,热影响区是接头最薄弱的部分,焊核区的硬度最高,而热影响区的硬度最低,焊缝金属发生回复再结晶使晶粒细化。断口分析表明,断裂发生在热影响区,由于搅拌头的旋转运动和热量的累积,该区存在晶粒长大、组织粗化现象。对工艺参数的优化实验表明,搅拌头旋转速度与焊接速度对接头性能的影响存在一定的适配关系,通过工艺参数的调整可以有效地控制热影响区的焊缝组织和改善焊接接头的性能。细晶强化是搅拌摩擦焊接头强度与韧性提高的主要原因。
The 661-T4 6061-T4 aluminum alloy plates were butt welded by friction stir welding (FSW) method. The microstructures of the welded joints and the base metal were compared with those of the welded joints by scanning electron microscopy (OM) and scanning electron microscopy (SEM) Fracture morphology and tensile properties at room temperature and microhardness were tested. The experimental results show that the suitable process parameters for the 6061-T4 aluminum alloy sheet are selected: the rotation speed of the stirrer during welding is 1200 r.min-1, the workpiece feed speed is 300 mm.min-1, Parameters obtained with the base material such as strength, toughness close to the base metal welded joints for the alloy used in key components of the vehicle provides a reliable process. The microstructure and properties of the weld zone in the FSW sheet joint are obviously better than those in the other zones. The HAZ is the weakest part of the joint. The hardness in the weld zone is the highest and the hardness in the heat affected zone is the lowest. The weld metal recovers and recrystallizes Granulation. Fracture analysis shows that the fracture occurred in the heat affected zone. Due to the rotational movement of the stirring head and the accumulation of heat, the grain growth and the coarsening of the structure exist in this zone. The optimization of the process parameters shows that there is a certain relationship between the rotating speed of stirrer and the welding speed on the performance of the joint. By adjusting the process parameters, the weld microstructure and the performance of the welded joint can be effectively controlled. Fine grain strengthening is the main reason for the increase of strength and toughness of friction stir welded joints.