激光束的入射方向及入射角度会直接影响焊缝熔池的形状及其流动形态，这会对焊缝成型与性能产生重要影响。

The incident direction and incident angle of the laser beam will directly affect the shape of the weld molten pool and its flow pattern, which will have an important impact on the formation and performance of weld joint.

为了了解激光束与焊缝的相对位置对焊缝的影响，我们做了两次实验，分别用非高反材料和高反材料进行测试。

In order to understand the effect of the relative position of the laser beam and the weld joint, we conducted two experiments with anti-reflection materials and non-anti-reflection materials.

上期回顾：

【Rayclass | 锐课堂】第14期：激光束与焊缝的相对位置对焊缝的影响（1）

本期【Rayclass | 锐课堂】我们再来看看高功率多模组连续激光器RFL-C4000（纤芯100μm）在焊接高反材料（铝合金为例）时受激光束入射相对位置对焊缝的影响规律。

前倾

Forward

后倾

Backward

图3  焊接铝合金时光束位置对熔深的影响

（图中横坐标数值表示光束入射角度值，“负值”表示光束前倾，“正值”表示光束后倾）

Graph 3 Effect of beam position on penetration and melting width when welding aluminum alloy

(The abscissa value indicates the incident angle of the beam, the negative value indicates the forward tilt of the beam, and the positive value indicates the backward tilt of the beam.)

从表2和图3可以看出，激光垂直入射焊接时的焊缝熔深最大，光束入射角度越大，熔深越浅，并且在同一入射角度时光束前倾相对于光束后倾的熔深大。

It can be seen from Table 2 and Graph 3 that the weld penetration is maximum when laser perpendicular incidence welding. Meanwhile, the larger the incident angle of the beam, the shallower the penetration, and at the same angle of incidence, the depth of fusion of beam forward is slightly smaller than beam backward.

首先需要明确，当激光垂直入射时，熔池的面积会大于光斑面积，主要是因为受到光斑直接作用的母材会形成初始的高温熔池，进而热传导至周边的母材区域使其熔化形成完全的准稳态熔池，如图4（a）所示；当激光束前倾入射时，初始状态是熔池内会建立一个有倾角的“小孔”，方向同样是向前，而小孔底部正上方的母材金属随即会受到小孔内部和周边高温金属和金属蒸汽的热辐射而熔化，最终形成一个开口面积大于光斑面积的准稳态熔池，如图4（b）所示，所以在激光束垂直入射和前倾入射两种情况下，激光束均会作用于液态金属熔池，其对激光束的吸收率远远高于未熔化的铝合金母材，此时两者之间熔深的比较原理类同于不锈钢激光自熔焊时的情况（见上期），即激光束垂直入射时焊缝的熔深大于激光束前倾时的熔深，并且激光束前倾入射时的倾角越大，熔深越小。

First of all, when the laser is incident vertically, the area of the molten pool will be larger than the spot area. The main reason is that the base material directly affected by the spot will form an initial high-temperature molten pool, and then heat is transferred to the surrounding base material region to melt it to form a complete quasi-steady-state molten pool, as shown in graph 4(a). When the laser beam is incident on the front, the initial state is that a small hole with an inclination is established in the molten pool. The base metal directly above the bottom of the keyhole will then be melted by the thermal radiation of the high-temperature metal and metal vapor inside and around the keyhole, eventually forming a quasi-steady melting pool with an opening area larger than the spot area, as shown in graph 4 (b). Therefore, in both the laser beam normal incidence and the forward tilting incident, the laser beam acts on the liquid metal bath, and its absorption rate to the laser beam is much higher than that of the unmelted aluminum alloy base material. At this time, the fusion depth of the weld bead when the laser beam is incident perpendicularly is larger than the depth of fusion when the laser beam is tilted forward, and the larger the inclination angle when the laser beam is forwardly incident, the smaller the depth of fusion.

图4 光束前倾与垂直入射对比图示

Graph. 4 Comparison of beam forward and vertical incidence

当激光束后倾入射时，如图5（a）中的激光束绿色部分就仅能够对铝合金母材进行预热， 此时会因为铝合金对激光束的高反特性损失相当部分的能量，而当激光束前倾入射时，如图5（b）中的激光束则会全部入射到液态熔池金属中，基于固态铝合金对激光的吸收率远远小于液态铝合金的前提下，此时激光束被吸收的能量会大于激光束后倾入射时的被吸收量，所以激光束后倾入射时焊缝的熔深小于激光束前倾时的熔深。当光束后倾角度变大时，光斑作用母材的面积会变大，其周边一定区域范围内的能量密度会更低，会有更大的范围内的激光不足以熔化铝合金母材，就会损失更多的能量，所以激光束后倾入射时，随着倾角的增大，焊缝熔深会减小，并且减小速度越来越快。

The graph 5(a) demonstrates the green part of the beam can only preheat the aluminum alloy base material when the laser beam is incident on the back, which will lose a considerable amount of energy due to the high inverse characteristics of the aluminum alloy to the laser beam. However, when the laser beam is tilted forward as shown in graph 5(b), the laser beam will all be incident on the liquid pool metal. Based on the premise that the absorption rate of the laser by the solid aluminum alloy is much smaller than that of the liquid aluminum alloy, the energy absorbed by the laser beam is greater than the absorbed amount when the laser beam is incident on the back-tilting direction. Therefore, the fusion depth of the weld when the laser beam is inclined backward is smaller than when the laser beam is tilted forward. At the same time, when the back-tilt angle of the beam becomes larger, the area of the spot acting on the base material becomes larger. The energy density in a certain area around it will be lower, and there will be more lasers in the range to melt the aluminum alloy base material, which will lose more energy. Therefore, when the laser beam is incident on the back tilt, as the tilt angle increases, the depth of fusion will decrease and the speed will decrease faster.

图5 光束前倾与垂直入射对比图示

Graph. 5 Comparison of beam forward and vertical incidence

从表2中可以看出，激光束前倾入射，并且倾角较大时，焊缝成型较好，内部无明显气孔，随着倾角的减小，焊缝内部会有明显的大气孔出现，并且焊缝成型变差，原因可能是因为倾角大时，熔池凝固速度变慢，气泡有足够的时间向外逸出，熔池也会充分的流动，使得焊缝成型较好；而当激光束后倾入射时，焊缝内部气孔虽然会有所改善，但是成型会变差，尤其是在倾角较大时，成型变的非常差，因为此时焊缝熔深变小很多，更有利气孔的逸出，但是焊缝熔池内的小孔会向后方倾斜，致使后方待凝固的熔池区域会因小孔的闭合坍塌产生较大的波动，进而导致焊缝成型差。

The table 2 demonstrate that when single laser welding aluminum alloy, there is no obvious bubble in the weld when laser beam is incident vertically and higher inclination. As the inclination decreases, there will be obvious atmospheric holes inside the weld. The reason is when the inclination angle is large, the solidification speed of the molten pool becomes slow, the bubbles have enough time to escape outward, and the molten pool also flows sufficiently, so that the weld bead is well formed. When the laser beam is incident on the back, the internal pores of the weld will be improved, but the molding will be worse, especially when the inclination is large. Because the fusion of depth becomes much smaller at this time, it is more favorable for the escape of the atmospheric holes, but the small holes in the weld pool will be inclined backward, so that the area of the molten pool to be solidified behind to cause large fluctuations due to the closure of the small holes.