脉冲激光点焊铝合金工艺特性研究

研究了几种特殊脉冲波形方式下，铝合金激光点焊焊点形态、尺寸的变化规律。实验结果表明，与矩形方波连续激光点焊相比，前期预制尖峰脉冲可以提高后期主脉冲阶段工件对激光能量的吸收效率，提高低功率下激光点焊的焊点稳定性;而后期的缓降脉冲波形能有效地减少焊点中的气孔和裂纹数量，但是增大了焊点表面的下塌量。缓升脉冲波形可以起到清理工件表面氧化膜的作用，减少焊点中氧化膜气孔的产生，并且能够减少焊点表面下塌量。结合缓升、缓降两种波形的优点，最后采用锯齿脉冲波形获得了无气孔、裂纹等缺陷的高质量焊点。

Effect of Pulse Shapes on Laser Spot Welding of Aluminum Alloy

Laser spot welding of aluminum alloy is difficult for its high optical reflection and thermal conductivity. The quality of the spot weld depends strongly on the condition of material surface. In this paper laser spot welding of aluminum alloy with different laser pulse shapes was carried out, and the relationship between the pulse shape and the quality of laser spot welds was investigated. Due to the high reflection of aluminum alloy the enhanced spike pulse shape, which has an initial spike of 1.8 kW laser power was used. The surface metal vaporized and keyhole formed, so the rest of laser power can be absorbed sufficiently. The results show that the repetition of laser spot weld was much better using this enhanced spike pulse shape. The ramp-up pulse shape can help to exclude the surface oxide film and stable the formation of spot weld. In addition, cool-down pulse shape was used to minimize the defects such as crack and porosity in the weld. However the surface crater of spot weld using cool-down pulse shape was obviously deeper than the rectangular pulse shape. At last, saw-like pulse shape, which combine the advantages of cool-down and ramp-up pulse shapes, was used and the quality of spot weld was excellent.