焊后热处理工艺和背部二次焊接对搅拌摩擦焊接7075-T651铝合金性能的影响

EFFECTS OF POST-WELD HEAT-TREATMENT AND SECOND-WELDING ON TENSILE PROPERTIES OF FRICTION STIR WELDED 7075-T651 ALUMINUM ALLOY

对8 mm厚7075-T651铝合金轧制板进行了搅拌摩擦焊接,重点研究了焊后热处理工艺和背部二次焊接对接头性能的影响．结果表明,焊接态接头致密没有缺陷,接头强度约为母材的71%．T6热处理后,焊核区出现由锯齿形裂纹和散孔组成的“S”线,随着固溶温度升高,“S”线愈加明显,并伴有晶粒异常长大现象．T6热处理后,接头硬度恢复到母材水平,但强度和延伸率显著下降,这是由于裂纹沿“S”线产生和扩展所致．在焊态样品背面进行二次焊接,可明显改善接头的力学性能．

8 mm thick 7075-T651 aluminum alloy rolled plate was friction stir welded, and the effects of post-weld heat-treatment and second-welding of the weld back on the tensile property were investigated. The results show that the single-welded sample is defect-free and the transverse strength of the weld is 71% of the base materials. However, a lazy ＂ S ＂ line appeared in the nugget zone as zigzag crack and discontinuous cavities after post-weld T6-treatment. With increasing solution temperature, the ＂ S ＂ line and abnormal grain growth became evident. After post-weld T6-treatment, the Vickers hardness of the weld was restored to the level of parent material, but the strength and elongation were significantly reduced due to the crack initiation and propagation along the ＂ S ＂ line. The tensile properties were greatly improved after second-welding of the weld back.