Dual-Laser Synergy in Dissimilar Al/Zn-Steel Brazing: Process Mechanisms & Quality Enhancement​

Researchers from Southern Methodist University in the United States published "Effect of dual laser beam on dissimilar welding-brazing of aluminum to galvanized steel" in Optics and Laser Technology.

01 Introduction
This study investigates the application of dual laser beams (cross-beam and linear-beam modes) in the dissimilar welding-brazing process of aluminum alloys and galvanized steel. Although conventional laser welding methods can join different materials, issues such as uneven heat input, poor joint quality, and the formation of intermetallic compounds (IMCs) remain challenging. The dual laser beam configuration, by altering the shape and distribution of the laser beam, holds potential to alleviate these problems. This research aims to evaluate the effects of different dual-beam configurations on the microstructure, mechanical properties, and surface quality of the joints, and explore their potential for industrial applications.

02 Full Overview
This paper studies the influence of cross-beam and linear-beam modes on the welding-brazing process between aluminum alloys and galvanized steel. A 4 kW IPG fiber laser was used to split the beam into two independent beams. Experiments showed that the cross-beam mode formed a thicker intermetallic compound layer at the aluminum/steel interface, while the linear-beam mode resulted in a thinner IMC layer. The cross-beam mode better controlled heat input, improved joint microstructure and IMC formation, and produced superior surface quality with lower surface roughness. Tensile test results indicated that joints welded with the cross-beam mode exhibited better ductility and fracture toughness, with fractures occurring at the aluminum/joint interface. In contrast, joints formed with the linear-beam mode were more brittle, fracturing at the steel/joint interface.

03 Image and Data Interpretation
Figure 1 shows the cross-section of a weld joint formed under the cross-beam laser mode. The welding quality is good, with no porosity observed. The aluminum base material was melted while the steel remained unmelted, demonstrating the characteristics of laser welding-brazing. The upper portion of the joint consists of filler metal mixed with aluminum, forming Al-Si-Fe alloys. The joint exhibited different microstructures in the top and bottom regions: dendritic α-Al and Al-Si eutectics at the top, and small Al particles dispersed with Si at the bottom.

Fig. 1. Microstructure of laser-welded joint in cross-beam mode at different magnifications.

Figure 2 presents the microstructure of the joint formed with the linear-beam mode. The aluminum dendrites appear more uniform and the penetration depth is greater. Compared with the cross-beam mode, the linear-beam laser power was more focused within the groove of the joint, resulting in remelting and resolidification, which produced a more consistent weld microstructure.

Fig. 2. Microstructure of laser-welded joint in straight-beam mode at different magnifications.

Figure 3 shows that the molten pool size in the linear-beam mode is larger than in the cross-beam mode. The lower temperature at the steel interface in the linear-beam configuration led to the formation of a thinner IMC layer. Furthermore, the cross-beam mode produced a shallower beam and wider weld, while the linear-beam mode covered a smaller weld area but with deeper penetration.

Fig. 3. (a) Numerical simulation and (b) experimental cross-section obtained via dual straight-laser-beam mode.

Figure 4 displays weld surfaces measured with an optical profilometer, comparing the surface effects of dual cross-beams and dual linear beams. The results demonstrate that dual cross-beams produced better surface quality due to the wider heat source, which helps preheat the substrate and improve wetting.

Fig. 4. 3D view and cross-section of joints captured by optical profilometer: (a) Al/Ni-plated Cu—straight beam, (b) Al/Ni-plated Cu—cross beam.

04 Conclusion
This study demonstrates that dual laser beam configurations offer significant advantages in dissimilar material welding. In particular, the cross-beam mode improves joint microstructure and mechanical properties, reduces defects, and enhances surface quality. This method effectively stabilizes IMC formation, decreases crack sensitivity in the joint, and enhances process adaptability. Experimental results also show that, compared to the linear-beam mode, the cross-beam mode improves welding efficiency while maintaining good joint quality. Although the cross-beam mode outperforms the linear-beam in many aspects, the linear-beam mode still has potential for specific applications. Future research should focus on optimizing dual laser beam parameters and exploring broader industrial applications to further enhance dissimilar material welding processes.

**--Cite the article published by 高能束加工技术 on February 2, 2025, in the WeChat public account "High-Energy Beam Processing Technology and Applications."