Due to high hot crack susceptibility of Al-Mg-Si alloys, autogenous welding by rectangular pulsed laser beam has not been generally successful in the removal of cracks. In this research, the effect of pulsed Nd:YAG laser parameters and preheating on the creation of hot cracks in the 6061-T6 aluminum alloy was investigated. The sample that was fabricated by the laser parameters including 1 Hz, 0.12 mm/s, 10 ms, and without preheating exhibited the highest cooling rate and the smallest dendrite arm spacing but no hot crack was observed. The tensile test specimens of this sample fractured at a point far from the weld metal and a decrease in the precipitation of silicon and magnesium in the inter-dendritic space and the reduction of thermal stresses resulted in the elimination of hot cracks. However, according to macro-scale models for the creation of hot cracks, preheating decreased the tensile stresses in the BTR (brittle temperature range), but increasing the preheating temperature led to increasing rather than decreasing the hot crack length. In this case, the formation of hydrogen porosity, the segregation of silicon and magnesium, and the creation of low melting point compounds were the important parameters affecting the hot crack initiation and growth.

中文翻译：

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矩形脉冲Nd：YAG激光束自生焊接6061-T6铝合金时的热裂纹

由于Al-Mg-Si合金的高热裂纹敏感性，矩形脉冲激光束的自生焊接在去除裂纹方面通常没有成功。在这项研究中，研究了Nd：YAG脉冲激光参数和预热对6061-T6铝合金中产生热裂纹的影响。由包括1 Hz，0.12 mm / s，10 ms的激光参数制造且未进行预热的样品显示出最高的冷却速率和最小的枝晶臂间距，但未观察到热裂纹。该样品的拉伸试样在远离焊接金属的位置断裂，并且树枝状晶间空间中硅和镁的沉淀减少，并且热应力的降低导致消除了热裂纹。然而，根据产生热裂纹的宏观模型，预热降低了BTR（脆性温度范围）中的拉应力，但预热温度的升高导致而不是减小了热裂纹的长度。在这种情况下，氢孔隙的形成，硅和镁的偏析以及低熔点化合物的产生是影响热裂纹萌生和生长的重要参数。