Abstract
Laser brazing is a critical process for joining Class-A automotive components, typically utilizing Cu-based filler wires, while the fundamental relationship between filler wire chemistry and the resulting joint microstructure remains insufficiently understood. This study investigated the influence of Si content on the microstructural evolution by comparing the joint microstructure with CuSi3 and Cu wires. Results revealed that Si modified both the interfacial reaction layer and braze metal. For both filler wires, the interfacial reaction layer was composed of Fe(Si) solid solution as a matrix, and the braze metal was composed of Cu matrix with dispersed Fe-rich phases/precipitates. Differently, the joint interface with CuSi3 wire was thinner, with some Cu-rich phases formed in the Fe(Si) matrix, and showed reduced Cu penetration into the steel base metal, indicating that Si inhibited the intermixing between Cu and Fe. Furthermore, the higher Si concentration within CuSi3 braze metal promoted the formation of secondary precipitates within the Fe-rich phases. These findings demonstrated that Si content is a critical factor for controlling interfacial reaction and braze metal precipitation morphology, providing a basis for optimizing wire selection in high-performance automotive joints.