针对紫铜激光焊高反射率问题，提出了一种纳秒激光直写表面辅助下紫铜激光焊方法. 利用纳秒激光对紫铜待焊区表面进行激光直写，产生覆盖有纳米颗粒的周期微结构，提高吸收率从而实现激光焊. 阐述了纳秒激光直写表面降反作用机理，研究了焊接工艺参数对焊缝成形的影响，对焊接接头的组织和力学性能进行了分析. 结果表明，纳秒激光直写表面能够有效降低紫铜对激光的反射率；随着焊接激光功率增加，焊缝成形由宽而浅变为窄而深；焊缝区结晶以铜晶粒为晶核呈柱状晶生长，且柱状晶尾部呈弯曲状指向焊接方向，并非指向中截面生长，树枝状束粗细均匀；通过线扫描发现表面纳秒激光直写处理对紫铜焊缝冶金行为几乎没有影响，仅在距离焊缝表面53 μm范围内存在少量O元素，而焊缝内部几乎没有氧等异质引入，均为紫铜的单相固溶体；接头的抗拉强度为母材的81.4%，焊缝中心硬度为65.8 HV0.1，断口表现为延性断裂，焊缝保持一定塑性.
In order to improve the laser absorption rate of copper, a method of copper laser welding assisted by the surface pretreated by the nanosecond laser direct writing was proposed. Nanosecond laser was used to write directly on the surface of copper to produce period microstructure covered by nanoparticles. The pretreated surface could effectively absorb the fiber laser and improve the laser absorption rate to ensure a smooth laser welding of copper. The mechanism of the pretreated surface reducing the reflection of copper was illustrated, the influence of welding process parameters on the weld formation was studied, and the microstructure and mechanical properties of the weld were analyzed. The results showed that surface nano-particles can effectively reduce the laser reflectivity of copper. With the increase of welding laser power, the weld appearance altered from a shape of wide- and-shallow to narrow-and-deep shape. The microstructure was dendritic crystals based on copper grain at the boundary of bond line at partial melting region, and the tails of dendritic crystals were curved towards the welding direction, instead of growing toward the axis of weld, and the bunches of dendritic crystals were uniform in thickness. Line scanning images showed that the treatment of laser direct writing barely had any effect on the metallurgical behavior of the copper welds, and there was only a small amount of oxygen in the range of 53 μm from the weld surface. Besides the single-phase solid solution of copper, there wasn't any heterogeneous such as oxygen introduced in the weld. The tensile strength of the joint was 81.4% of that of the base metal, and the hardness of the weld center was 65.8HV0.1. The fracture was ductile, and the weld remained certain plasticity.
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