搅拌针长度对搅拌摩擦搭接焊铝合金/钢异种材料接头组织性能的影响

通过搅拌摩擦搭接焊接6061铝合金/QP980钢异种材料，讨论了搅拌针长度（1.5和2.1 mm）对焊接接头组织和性能的影响。结果表明，6061铝合金/QP980钢搅拌摩擦搭接焊接头分为3层结构：上层为铝合金层，中间层为Fe、Al及金属间化合物混合层状结构，下层为钢层。其中，当搅拌针长2.1 mm时，铝合金层含有散落的钢碎片。在中间层检测到2种金属间化合物，靠近Al的深灰色层为Fe₄Al₁₃相，靠近钢的是Fe₂Al₅相。随着搅拌针长度的增加，接头的失效载荷从4 kN降低到3 kN。短探针焊接的接头在接合界面处断裂，而长探针焊接的接头在铝和钢的混合区断裂。孔洞缺陷和钢碎片是导致断裂位置发生变化的主要原因。此外，嵌入铝基体中的铁屑在变形过程中起应力集中和裂纹萌生的作用，降低了接头的力学性能。

Effect of Probe Length on Microstructure and Mechanical Properties of Friction Stir Lap-Welded Aluminum Alloy and Steel

The 6061 aluminum alloy and QP980 steel were lap-welded by friction stir welding (FSW) technique, and the effect of different probe lengths of 1.5 and 2.1 mm on the microstructures and properties of welded joints was investigated. Results show that the FSW lap-welded joints of 6061 aluminum alloy/QP980 steel consist of three layers: the upper layer is aluminum alloy, the middle layer is composed of Fe, Al, and intermetallic compounds, and the under layer is steel. When the probe length is 2.1 mm, the aluminum layer contains scattered steel fragments. Two kinds of intermetallic compounds can be detected: the dark gray layer close to Al is Fe₄Al₁₃ phase, and the one close to steel is Fe₂Al₅ phase. With extending the probe length, the fracture load of the joints is decreased from 4 kN to 3 kN. The joints welded by short probe fracture at the bonding interface, whereas those welded by long probe fracture at the mixture zone of Al and steel. The fracture position change is caused by the porosities and steel fragments. In addition, the steel fragments embedded in the Al matrix promote the stress concentration and crack initiation during the deformation process, therefore decreasing the mechanical properties of the joints.