焊后热处理对AA7075铝合金DP-MIG焊接接头组织及力学性能的影响

Effect of post-weld heat treatment on microstructure and mechanical properties of welded joint of 7075 aluminum alloy by double-pulsed metal inert-gas welding process

关键词:  双脉冲  焊后热处理  显微组织  接头强度系数  软化区

Key words:  double-pulse  post-weld heat treatment  microstructure  joint strength efficiency  soften zone

摘要:

采用双脉冲熔化极精性气体保护焊（DP-MIG）工艺方法焊接AA7075-T651铝合金，焊接试板采用固溶处理（480℃×50 min）后水淬，再进行（80℃×24 h）+（120℃×24 h）两级人工时效热处理，通过金相观察、扫描电镜观察、X射线衍射分析、拉伸试验以及硬度测试，研究焊后热处理（PWHT）工艺对焊接接头显微组织及力学性能的影响.结果表明，焊缝区经热处理后，晶粒由枝晶向等轴晶转变，晶界处非平衡第二相溶解，晶界变细，焊缝显微组织特性改善明显；焊接接头经热处理后，抗拉强度由342.5 MPa提高到490 MPa，接头强度系数为0.872，焊缝软化区硬度得到较大改善，焊接接头力学性能有显著提升.

Abstract:

Double-pulsed metal inert-gas welding was used to weld AA7075-T651 aluminum alloy, and the welding samples was treated by solid solution treatment(480℃×50 min) and water quenching, then double-aging heat treatment(80℃×24 h)+(120℃×24 h). The effects of post weld heat treatment (PWHT) on microstructure and mechanical properties of welded joints were investigated by means of optical microscopy(OM), scanning electron microscopy(SEM), X-ray diffraction analysis, tensile test and micro-hardness measurement. The results shows that the grains are changed from dendrite to isometric crystal, and the non-equilibrium second phase is dissolved,the grain boundary becomes narrower and finer after post-weld heat treatment, and the microstructure characteristics of the welded joint are improved obviously. After heat treatment, the tensile strength of the welded joint increases from 342.5 MPa to 490 MPa, and the strength coefficient of the welded joint is up to 0.872. The micro-hardness of the weld softening zone is greatly improved, and the mechanical properties of the welded joint are significantly improved.