Revealing grains and very fine dendrites in a solidified weld metal of aluminum-magnesium-silicon alloys is difficult and thus, there is no evidence to validate the micro- and meso-scale physical models for hot cracks. In this research, the effect of preheating on the microstructure and hot crack creation in the pulsed laser welding of AA 6061 was investigated by an optical microscope and field emission electron microscopy. Etching was carried out in the gas phase using fresh Keller’s reagent for 600 s. The results showed that the grain size of the weld metal was proportional to the grain size of the base metal and was independent of the preheating temperature. Hot cracks passed the grain boundaries of the weld and the base metal. Lower solidification rates in the preheated samples led to coarser arm spacing; therefore, a lower cooling rate. Despite the results predicted by the micro and meso-scale models, lower cooling rates resulted in increased hot cracks. The cracks could grow in the weld metal after solidification; therefore, hot cracks were larger than predicted by the hot crack prediction models.

很难在铝镁硅合金的凝固焊接金属中显示晶粒和非常细的树枝状晶体，因此，没有证据可以验证热裂纹的微观和中观物理模型。在这项研究中，通过光学显微镜和场发射电子显微镜研究了预热对AA 6061脉冲激光焊接中显微组织和产生热裂纹的影响。使用新鲜的Keller's试剂在气相中蚀刻600 s。结果表明，焊接金属的晶粒尺寸与母材的晶粒尺寸成比例，并且与预热温度无关。热裂纹穿过焊缝和母材的晶界。预热样品中较低的凝固速率导致较粗的臂间距；因此，降低了冷却速度。尽管微观和中尺度模型预测了结果，但较低的冷却速率导致热裂纹增加。凝固后，焊缝金属中可能会出现裂纹。因此，热裂纹比热裂纹预测模型预测的要大。