含Sc高强铝合金薄板TIG焊与FSW接头组织与性能对比研究

Microstructure and Mechanical Properties of TIG and Friction Stir Welded Joints of Sc-contained High Strength Aluminum Alloy Sheet

分别对3mm厚的Al-Zn-Mg-Cu-Sc高强铝合金薄板进行钨极惰性气体保护(Tungsteninertgas,TIG)焊与搅拌摩擦焊接(Friction stir welding,FSW),对比分析了两种焊接工艺下接头的微观组织与力学性能。结果表明:两种工艺都能获得无缺陷的接头。TIG焊核区晶粒粗大;硬度分布呈"M"形,中心值降至125HV,最低值出现在热影响区(Heat-affected zone,HAZ)(约110HV);拉伸时样品断在HAZ,接头强度约为417MPa,为母材的71%。FSW焊核区为等轴细晶;硬度分布呈典型"W"型,最低值亦出现在HAZ(约115HV),且随焊速的提高而提高;在400~1 200r/min下均有可能获得高强度接头,其中转速1 200r/min、焊速200mm/min下接头强度最高(458MPa),为母材的79%,拉伸样品断在HAZ。当焊速过快时,由于合金变形能力差,焊核区易出现缺陷,导致拉伸时接头过早断裂于焊核区中心。

3 mm thick Al-Zn-Mg-Cu-Sc alloy plates were subjected to tungsten inert gas welding(TIG) and friction stir welding(FSW), respectively. The microstructure and mechanical properties of the TIG and FSW joints were investigated. The results showed that defect-free joints of both TIG and FSW were acquired. For the TIG joint, the nugget zone(NZ) was characterized with coarsened grains, the hardness distribution exhibited "M" shape with low hardness value in the center(~125 HV), and the lowest hardness zone(LHZ, ~110 HV) located in the heat affected zone(HAZ);the ultimate tensile strength(UTS) of 417 MPa was obtained, ~71% of the BM. For the FSW joints, the NZs were characterized with exquiaxed fine grains, and the grain sizes decreased with increasing the welding speed;the hardness distribution presented "W" shape with the LHZ located in the HAZ(~115 HV). FSW joints with high strength could be obtained under the rotation rates of 400-1 200 r/min, and the highest UTS of 458 MPa was achieved under the rotation rate of 1 200 r/min and welding speed of 200 mm/min, ~79% of the BM. When the welding speed was too fast, defects were likely to appear in the NZs due to the poor deformation ability of the alloy, resulting in the premature failure of tensile samples in the center of the NZs.