Effect of Brass Solder Composition on Quality in Laser Welding of Solar Panel Busbar

In order to reveal the action mechanism of different brass solder compositions on the microstructure of weld joints in unleaded-tin-coated coppers brazing-stitch welding, the laser welding process of solar panel busbar was studied by using three different coated brass solders: Sn-37Bi-3Ag, Sn-42Bi-3Ag and Sn-47Bi-3Ag. Scanning electron microscope, energy spectrometer, X-ray diffractometer, tensile testing machine and Vickers microhardness tester were used to test and analyze the influence of Bi element content on the microstructure and mechanical properties of weld joints in solar panel busbar brazing-stitch welding. The results show that: (1) With the increase of Bi element content, the wettability of soldering ceam is gradually improved, and the weld joints eutectic mainly consists of SnAg phase, Ag3Sn phase, Cu6Sn5 phase, Cu3Sn phase, SnAgCu phase, β-Sn sosoloid and Bi with rhombic layered structure. (2) The fracture of weld joints occurred at the interconnection belt side, it presents brittle and ductile mixed fracture. With the decrease of Bi element content, the tensile strength of weld joints gradually increased, and the maximum tensile strength of weld joints was 212 MPa. (3) The of weld joints decreases gradually from the busbar side to the interconnection belt side, and the highest microhardness of weld joints appears at the interface layer, it can reach 330.1 HV. With the decrease of Bi element content, the microhardness of weld joints gradually increased. This paper provides a scientific basis for the optimal selection and use of busbars in solar panels high-quality laser welding.