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已有研究表明在镁合金、铝合金及铜合金等高反射率材料激光焊接中,通过采用适当的功率调制措施可以增大熔深、减少飞溅和气孔等缺陷。本研究对这一现象背后的物理机制进行了初步探索。基于三元二次正交回归试验设计,进行了AZ31镁合金的正弦调制激光焊试验。获得了平均功率(P_A)、调制振幅(A)和调制频率(F)对焊缝横截面面积(A_(FZ))的影响规律。结果表明:P_A较小时功率调制措施可以显著改善焊接过程能量耦合效率,随着P_A的增大功率调制的促进作用减弱甚至消失;P_A较小时“小振幅+高频率”和“大振幅+低频率”的2种条件都可以增大焊缝A_(FZ)。获得并比较了频率8 Hz正弦调制焊接在“不锈钢(反射率约60%)+镁合金(反射率约80%)”双金属试板中形成的焊缝纵截面形貌。发现功率从瞬时最大值开始减小时,低反射率材料2205中的熔深马上开始同步减小,而高反射率材料AZ31中熔深开始减小的时刻则滞后了0.036 s(约占一个正弦周期的30%)。分析认为,高反射率材料激光焊过程中利用大于AP的瞬时功率峰值形成大深宽比小孔后会使激光在小孔内反射次数增加,因此在激光瞬时功率下降的过程中也可以使大深宽比小孔继续维持大约三分之一个正弦周期。大深宽比小孔能够形成并且在较长时间内维持存在是调制措施能够改善高反射率材料激光焊能量耦合效率的关键所在。
Studies have shown that in the laser welding of high reflectivity materials such as magnesium alloy, aluminum alloy and copper alloy, the appropriate power modulation measures can increase the penetration depth and reduce the defects such as splashing and porosity. The research explores the physical mechanism behind this phenomenon. Based on the triple quadratic regression experimental design, the sinusoidal modulation laser welding test of AZ31 magnesium alloy was carried out. The influences of average power (P_A), modulation amplitude (A) and modulation frequency (F) on the weld cross section area (A_ (FZ)) were obtained. The results show that when P_A is small, the power modulation measures can significantly improve the energy coupling efficiency of the welding process, with the acceleration of P_A weakening or even disappearing. When P_A is small, “small amplitude + high frequency” and “large amplitude + Low frequency ”of the two kinds of conditions can increase the weld A_ (FZ). The longitudinal section of the weld is obtained and compared with a sinusoidal modulation of frequency 8 Hz welded in a stainless steel (reflectivity of about 60%) + magnesium alloy (reflectivity of about 80%) "bimetal. When the power was found to decrease from the instantaneous maximum, the melt depth in the low-reflectivity material 2205 immediately started to decrease synchronously, while the time at which the penetration of the high-reflectivity material AZ31 started to decrease lagged by 0.036 s (about one sinusoidal period Of 30%). The analysis shows that the laser with high reflectivity during the laser welding process using instantaneous power peak greater than the AP to form a large aspect ratio of the hole will make the laser reflection in the hole increased, so the laser power instantaneous decline can also make large Aspect ratio holes continue to maintain about one-third of a sine cycle. Large aspect ratio apertures can be formed and maintained over a long period of time. The key to modulation efficiency is to improve the coupling efficiency of laser welding of high reflectivity materials.