转速对 7075-T651 铝合金搅拌摩擦焊接件内部残余应力分布的影响

目的掌握铝合金搅拌摩擦焊接板内部残余应力的分布,为控制焊接残余应力、改进焊接工艺和提高焊接件质量。方法以13.6 mm厚的7075-T651铝合金为研究对象,用短波长X射线衍射技术,对在不同搅拌头转速下搅拌摩擦焊接板内部的残余应力进行了无损测试,并对焊接接头在板厚中心层上的微观组织和显微硬度进行了研究。结果在垂直于焊缝截面上的显微硬度均呈"W"型分布,焊核区的显微硬度高于其两侧的热机械影响区和热影响区,但低于母材区的硬度;随着转速的增大,接头硬度的最小值减小,低硬度区的范围越大。横向残余应力绝对值整体小于焊接方向;焊核区为正应力,热机械影响区残余应力减小且变化梯度最大;残余应力的极大值位于热影响区和热机械影响区的交界处;残余应力极大值与硬度最小值的位置重合。结论通过残余应力的无损检测分析,不仅可以直接获得加工件内部应力分布,还可以间接获得加工件内部的加工缺陷情况,为改进加工工艺、提高成形精度提供依据。

Effect of Rotation Speed on the Residual Stress Distribution of Friction Stir Welded AA7075-T651 Plates

In order to control the residual stress, develop the welding process and improve the quality of the weldments, the distributions of residual stress of friction stir welded aluminum alloy plates were investigated. The residual stress distributions of friction stir weldments of 13.6-mm-thick AA7075-T651 plates at different rotate speed were measured non-destructively using short-wavelength X-ray diffraction method. What is more, the microstructure and microhardness in the middle layer of thickness of the weld joint was also studied. Results show that the profile of the microhardness is W shape and the values of hardness in weld nugget zone are bigger than those in thermo-mechanically affected zone and heat affected zone but lower than those in parent material. The minimum of microhardness increases and the soft region expands with the increase of rotation speed. The absolute values of residual stress in transverse direction are smaller than longitudinal direction. Tensile residual stress exists in the weld nugget zone and decreases in thermo-mechanically affected zone in which residual stress varies intensely. In addition, maximum of residual stress locates on the boundary of thermo-mechanically affected zone and heat affected zone, where the minimum microhardness also locates. By the non-destructive analysis of residual stress, residual stress distribution could be investigated directly and the potential internal defect could also be perceived, which can be employed as the basis of developing the processing and improving the accuracy of forming.