铝合金/钢搅拌摩擦焊与冷金属过渡焊搭接接头的拉剪载荷及显微组织分析

分别采用搅拌摩擦焊和冷金属过渡焊进行铝合金与镀锌钢的焊接试验,通过对焊缝截面显微组织、界面层成分及显微硬度的对比分析,研究影响焊接接头拉剪载荷和失效形式的因素。结果表明:搅拌摩擦焊接头的拉剪载荷接近于母材,焊缝晶粒细小、组织致密,显微硬度高于冷金属过渡焊接头,铝合金-钢异种金属界面层的结合为通过"洋葱瓣"状结构的机械咬合和冶金结合,界面层厚度约为20μm,为Al-Zn固溶体;冷金属过渡焊接头的拉剪载荷较铝母材降低了37.8%,在熔合线附近断裂,熔合线附近为柱状晶,焊缝根部存在热裂纹,显微硬度较铝母材的降低了30%,界面层厚度约为5μm,为Al-Fe金属间化合物。

Tensile-shear load and microstructure comparison between FSW and CMT lap joints of aluminum/steel

Friction stir welding （FSW） and cold metal transfer （CMT） were employed in dissimilar metal welding experiments of aluminum alloy and Zn-coated steel, and the effect of tensile-shear strength and failure modes were studied through the comparision of mierostructure, micro hardness and interface layer. The results show that the tensile loads of FSW ioints are close to base metal, grains are tiny, tissue is dandified, and CMT welding joints are reduced by 37.8% compared with aluminum base materi al. Onion petal structures in FSW welding joints form a mechanical connection. The micro hardness is higher than CMT joints. The interface is connected by mechanical and metallurgical reaction. The Al-Zn solid solution thickness of interface is 20 μm. The tensile-shear loads are reduced by 37.8% compared with Aluminum base metal. Fracture appears in the vicinity of the fusion line. The grains around the fusion line are columnar crystals. There is a hot crack at joint root, the micro hardness is reduced by 30% compared with base metal, and the A1-Fe intermetallic compound thickness of interface is about 5 μm.