铝/钢表面预置粉末激光焊接头的组织与性能

Microstructure and mechanical properties of laser welding joint with aluminum/steel surface preset filler powder addition

针对铝/钢焊接的技术难点,采用铝表面预置AlSi12Mg1.5粉、铝/钢层间预置Sn粉的方法,对1.2 mm厚6016铝合金和1.4 mm厚DP590双相钢进行铝上钢下搭接、铝/钢表面同时预置粉末的光纤激光焊接试验,分析接头成形、连接界面显微组织及力学性能;利用ANSYS有限元软件,建立铝/钢激光焊接瞬态有限元模型,计算接头温度场分布;利用基于密度泛函理论的第一性原理方法,计算预置粉末新形成物相FeSn、Fe3Sn及FeAl3、Fe2Al5等化合物的模量和热力学性能。结果表明:在激光头沿焊接方向偏转10°、激光功率2750 W、焊接速度32 mm/s、离焦量2 mm、Ar保护气体流量20 L/min条件下,铝/钢表面同时预置粉末可实现6016铝合金与DP590双相钢有效连接,无明显气孔、裂纹等缺陷,接头平均线载荷54.16 N/mm,与铝表面预置AlSi12Mg1.5粉、铝/钢层间未预置Sn粉相比,接头性能提高1.6倍;铝表面预置AlSi12Mg1.5粉,焊接元素光谱相对强度和等离子体的电子密度增大,预置AlSi12Mg1.5粉增加上层铝对激光的吸收率,改善焊缝表面成形;当铝/钢层间预置Sn粉时,铝、钢均达到熔化状态,上层铝液和下层钢液的熔合宽度加大,铝/钢横向结合面积增加,焊合率提高;此外,焊缝区晶粒细小,接头界面Fe-Al化合物的层厚度减少,生成高温下结构稳定的FeSn和Fe3Sn等延性新相,因而同时预置粉末获得了较好的铝/钢接头性能。

In view of the technical difficulties of aluminum/steel welding, the 1.2 mm-thick 6016 aluminum alloy and 1.4 mm-thick DP590 dual phase steel was laser welded by adding AlSi12Mg1.5 powder to aluminum surface and Sn powder to aluminum/steel interlayer layer with lap joint applied with aluminum sheet on the top and steel sheet at the bottom. The weld appearance, microstructure and mechanical properties of welding joint were studied. The temperature field distribution of aluminum/steel joints was calculated by establishing the transient finite element model of aluminum/steel laser welding based on ANSYS finite element software. The modulus and thermodynamic properties of compounds such as FeSn, Fe3Sn, FeAl3 and Fe2Al5, were calculated by using first–principles method based on density functional theory.The results indicate that 6016 aluminum alloy and DP590 double phase steel can be effectively connected with preset filler powder to aluminum/steel surface, no obvious porosity, cracks, and other defects are seen when the welding power is 2750 W, welding speed is 32 mm/s, the defocus distance is-2.0 mm, Ar gas acts as the protection gas with flow rate 20 L/min, and laser deflection is along welding direction 10°. The average linear load of the welding sample with aluminum/steel surface preset filler powder reaches 54.16 N/mm. Compared to that without aluminum/steel interlayer powder addition, the average shear strength of weld joint increases by 1.6 times. The relative intensity of spectra and electron density of plasma increases, which shows that the laser energy absorption rate increases by adding AlSi12Mg1.5 powder to the aluminum surface. Thus, the surface of the weld is improved. When Sn powder is added to aluminum/steel interlayer layer, the aluminum and steel are both melted, the fusion width of the upper aluminum and the lower steel increases, the combined area of aluminum/steel increases, and the welding rate is improved. In addition, grain size of weld zone is fine, Fe-Al compound layer thickness decreases. FeSn and Fe3Sn compounds has better ductility and is more stable than that of Fe-Al compounds at high temperature, which can improve the mechanical properties of weld joint.