Z形扫描在换向时焊道发生了较大的变形，这是因为换向时激光连续作用，热积累影响比较严重。由于激光扫描起点在左侧，三道扫描线至少有两道都是以右侧为终点，因此右侧的温度在扫描结束后始终高于左侧，右侧的热膨胀也明显要高于左侧。单向扫描时，热应力主要集中在顶面和底面右端；Z形扫描时，热应力则分散在在底面和顶面两端。

The weld bead of Z-scan has a large deformation during commutation, which is due to the continuous effect of laser during commutation and the serious influence of heat accumulation. Since the starting point of laser scanning is on the left side, and at least two of the three scanning lines end at the right side, the temperature on the right side is always higher than that on the left side after scanning, and the thermal expansion on the right side is also significantly higher than that on the left side. During unidirectional scanning, the thermal stress is mainly concentrated on the top and the right end of the bottom. During Z-shape scanning, the thermal stress is distributed at both ends of the bottom