材料期刊网

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(PA)、调制振幅(A)和调制频率(F)对焊缝横截面面积(AFZ)的影响规律.结果表明:PA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PA的增大功率调制的促进作用减弱甚至消失;PA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AFZ.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.

Previous researches show that appropriate power modulation methods can increase the weld penetration and decrease the drawbacks of splatters and pores in laser welding for the high reflectivity materials such as magnesium alloy,aluminium alloy and copper alloy.This paper conducted tentative explorations to the underlying physical mechanism of this phenomenon.The sine modulated laser welding test of AZ31 was developed based on ternary quadratic regression design and the influence of average power (PA),modulation amplitude (A) and frequency (F) on welding joint cross-sectional fusion zone area (AFZ) were studied.The results show that power modulation can obviously improve energy coupling in the lower PA welding process,while this improvement will be weakened and even disappear with PA increasing.Both "small amplitude + high frequency" and "large amplitude + low frequency" can increase the cross-sectional AFZ when welding in the case of low PA.The longitudinal-sectional morphology of "stainless steel (reflectivity:60％) + Mg alloy (reflectivity:80％) " bimetallic specimen welded joint obtained in the sine modulated welding of 8 Hz was compared.It is demonstrated that when the power decreases from the peak value,the weld depth in lower reflectivity materials 2205 decreases synchronously,but the decreasing moment of weld depth in high reflectivity materials AZ31 delays about 0.036 s (about 30％ of a sine period).The phenomenon may be attributed to that a deeper keyhole could be formed by the instantaneous peak power value,which increases the number of reflection of laser beam in keyhole.Then,in spite of the declining of transient laser power,the high aspect ratio keyhole will be maintained for about 1/3 of a sine period due to the enhanced energy coupling efficiency.It is the key point for power modulation to improve the energy coupling efficiency of high reflectivity materials that the high aspect ratio keyhole can be formed and maintained for a long time