Fe/Al难熔合、易生成Fe-Al脆性金属间化合物是钢/铝异种金属优质高效焊接亟待解决的技术难题。对厚度分别为5 mm、6 mm的低碳钢和铝合金板进行了对接处开设坡口、并在界面结合处预置Si粉的光纤激光焊接实验研究，通过调整焊接工艺参数和预置粉末得到成形良好的焊缝。利用卧式金相显微镜、电子显微硬度仪、扫描电镜、X射线衍射仪等设备对焊缝及母材区进行了观察与检测。结果发现：在激光功率为1.8~2.0 kW，焊接速度8~10 mm/s，离焦量-2.0 mm，Ar为保护气体且流量为15 L/min，光斑偏向钢侧距界面结合处0.2 mm的工艺条件下，激光焊接钢/铝异种板材，可实现钢/铝熔合，焊接类型为热传导焊，焊缝区域晶粒细小，硬度高于两侧热影响区及母材，钢/铝结合界面分界线明显，界面处熔化金属互相扩散嵌入母材，呈齿轮式“啮合”态连接在一起。对钢/铝实施热传导焊，可有效控制熔池中Fe、Al熔化量；预置Si粉改善了焊池熔化态下的流动性，熔化金属易于在结合界面铺展，钢/铝焊缝区形成了结构稳定的Al9Si、Fe0.9Si0.1化合物，抑制了Fe-Al脆性金属间化合物的生成。

Technical problems like difficulty of fusion and brittle intermetallic compounds between Fe and Al are urgently to be solved in order to get high quality steel-to-aluminun weld seam with high efficiency. Low-carbon steel and aluminun alloy sheet (thicknesses are 5 mm and 6 mm, respectively) are welded in butt way by a fiber laser. Welding conducted with Si powder as the filler placed in the end before welding is also researched. Good welding beads have been obtained through adjusting the process parameters and pre-filling Si powder. The welding bead is detected and observed by metallurgical microscope, scanning electron microscope, X-ray diffraction and some other ways. The results indicate that dissimilar steel and aluminun can be connected by laser welding under heat conduction welding mode under the conditions that laser power is 1.8~2.0 kW, welding speed is 8~10 mm/s, defocusing is -2 mm, protective gas is Ar, gas flow rate is 15 L/min and offset to crevice between steel and aluminun is 0.2 mm. The grains in weld zone are fine. Micro-hardness in weld zone is higher than those in heat affected zone and base material. The boundary between steel and aluminum is clear. Two base materials are combined by the molten metal, embedded in each other like gears. The quantities of the melting metals Fe and Al in the pool are controlled. The fluidity of the pool is improved by the Si powder filler and it is good for melting metal to spread out in the end of the sheets. Compounds of Al9Si and Fe0.9Si0.1 with better stability are found and the generation of intermetallic compounds of Fe-Al is inhibited.