焊后热处理对AA7204-T4铝合金搅拌摩擦焊接头组织与力学性能的影响

Effects of post-weld heat treatment on microstructures and mechanical properties of AA7204-T4 aluminum alloy FSW joint

采用搅拌摩擦焊对AA7204-T4铝合金板材进行焊接,研究焊后热处理对FSW接头组织与力学性能的影响。结果表明:焊后(AW)态焊核区平均晶粒尺寸和再结晶分数分别为4.7μm和81.9%,焊后直接人工时效(AA)后二者分别为4.8μm和82.4%,焊后固溶+人工时效(SAA)后分别为5.9μm和86.5%,AA态并未对焊核区的晶粒结构产生明显的影响,而SAA态则使其分别提高了25.5%和5.6%。AW态,AA态和SAA态接头抗拉强度分别为296.6,318.2 MPa和357.4 MPa,AA态对接头力学性能提升有限,而SAA态则有效提升接头力学性能,焊接系数达92.0%。焊后固溶淬火导致接头连接界面"S"线处产生微裂纹,接头断裂于此,且伸长率严重降低。

AA7204-T4 aluminum alloy plates were welded by friction stir welding(FSW), and the effect of post-weld heat treatment on the microstructure and mechanical properties of the FSW joints were studied. The results show that the average grain size(AGS) and recrystallization fraction of nugget zone(NZ) are 4.7 μm and 81.9% in as-welded(AW) treatment, 4.8 μm and 82.4% under the post-weld artificial aging(AA) treatment, 5.9 μm and 86.5% under the heat treatment of solid solution followed by artificial aging(SAA), respectively. The grain structure of NZ is not obviously affected by AA treatment, and the AGS and recrystallization fraction of NZ increase by 25.5% and 5.6% under SAA treatment. The ultimate tensile strength(UTS) of the FSW joints are 296.6, 318.2, 357.4 MPa under the heat treatments of AW, AA and SAA, respectively. The improvement of the mechanical properties of FSW joints is limited by AA treatment, while that can be effectively improved by SAA treatment which leads to the welding coefficient reaching 92.0%. Additionally, the microcracks tend to generate on the "S" line under the effect of water quenching after solid solution, which would lead to the fracture location at this zone and the serious decrease of the elongation.