滚动轧制对铝合金搅拌摩擦焊接头性能的影响

Effect of rolling on friction stir welded joints of aluminum alloy

关键词:  铝合金7050|搅拌摩擦焊|滚动轧制|组织|力学性能

Key words:  7050 aluminum alloy|friction stir welding|rolling|microstructure|mechanical properties

摘要:

采用自制滚动轧制头对5 mm厚铝合金7050搅拌摩擦焊接头的上表面及背面进行滚动轧制，并与其焊接态的接头作对比，研究了滚动轧制对焊接接头性能的影响. 结果表明，滚动轧制后接头表面的粗糙度由最大9.58 μm降低到平均约0.85 μm. 表层发生了剧烈的塑性变形，晶粒明显细化形成约200 μm厚的细晶层，亚表层晶粒细化程度降低，在焊核区伴有剪切带产生. 接头表层硬度明显提高，其平均硬度高达HV210，相比轧制前硬度HV110提高了91%. 接头表层残余应力由原来的拉应力转变为压应力，最大残余压应力场深度约为200 μm. 疲劳源由表层移至亚表层，疲劳寿命显著提高.

Abstract:

The upper and back surface of a friction stir welded joint of 5 mm thick 7050 aluminum alloy were rolled by a self-made rolling head. It was compared with the welded joints without rolling. The effect of rolling on the performance of welded joints was studied. The results showed that the roughness of joint surface was reduced from 9.58 μm (maximum value) to 0.85 μm (mean value). The surface layer happened severe plastic deformation, and the grains were remarkably refined to form a fine grain layer of about 200 μm thick. The grain refinement of the subsurface layer was reduced, and a shear band was generated in the weld nugget zone. The hardness of the joint surface was obviously improved, and the average hardness was as high as HV210, which was 91% higher than the hardness HV110 before rolling. The residual stress of the joint surface changed from the original tensile stress to the compressive stress, and the maximum residual compressive stress field depth was about 200 μm. The source was moved from the surface layer to the subsurface layer, and the fatigue life was significantly improved.