A Comparative Study of the Heat Input During Laser Welding of Aeronautical Aluminum Alloy AA6013-T4

ABSTRACT The heat input is the amount of energy supplied per unit length of the welded workpiece. In this study, the effect of two different heat inputs in laser beam welding of a high strength aluminum alloy AA6013-T4 was evaluated from macrostructural and microstructural points of view. The experiments were performed using a continuous wave 2 kW Yb-fiber laser with 100 µm spot size on the upper surface of the workpiece. Keeping the heat input at a given level, 13 or 30 J/mm, the laser power was changed from 650 W to 2 kW and the welding speed from 33 to 150 mm/s. In the condition of higher heat input 30 J/mm it was possible to obtain both cutting and welding processes. For 13 J/mm, welding processes were obtained in conduction and keyhole modes. The equiaxed grain fraction changed with changing speed for the same heat input. The laser processing induced a decrease in the hardness of the weld bead of about 25% due to the solubilization of the precipitates. The estimated absorptivities of the laser beam in the liquid aluminum changed largely with experimental conditions, from 4.6% to 10.5%, being the most significant source of error in measuring the real amount of energy absorbed in the process. For the same heat input the macrostructure of the welded surfaces, i.e., humps and dropouts, changed as well. All these facts indicate that the heat input is not a convenient method to parameterize the laser beam welding parameters aiming the same weld features.

摘要 热输入指焊接工件单位长度所接收的总能量。本研究从宏观组织与微观组织两个维度，评估了两种不同热输入工况对高强度铝合金AA6013-T4激光束焊接过程的影响。实验采用功率为2 kW的连续波Yb光纤激光器，将工件上表面的光斑尺寸设为100 µm。将热输入固定为13 J/mm或30 J/mm两个水平，同步调整激光功率（650 W至2 kW）与焊接速度（33 mm/s至150 mm/s）。当热输入为30 J/mm的较高水平时，可同时实现切割与焊接两种工艺；而热输入为13 J/mm时，则可获得传导型与锁孔型两类焊接模式。在相同热输入条件下，等轴晶占比会随焊接速度的变化而改变。激光加工会因析出相发生固溶，使焊道硬度降低约25%。液态铝对激光束的预估吸收率随实验工况大幅波动，范围为4.6%至10.5%，该因素是测量焊接过程实际吸收能量时误差的最主要来源。在相同热输入下，焊接表面的宏观形貌缺陷（如驼峰与欠焊）同样会发生变化。综合以上所有现象可知，若以获得一致的焊缝性能为目标，采用热输入作为激光束焊接参数的表征方式并不具备合理性。