Microstructure and properties of stainless steel sheet laser soldering joint

Laser soldering was used to seal the lap joint of 304 stainless steel sheet, and the microstructure and shearing property of soldering joints were investigated. The results showed that with suitable laser beam tilt angle 60° and defocusing distance 300 mm, the laser heat input can be effectively reduced thus, ensuring a successful completion of laser soldering of 304 stainless steel sheet with a filling depth of 5 mm, and the appearance of the joint is smooth and full. The color of the joint is similar to that of the base metal, and no extra coating is needed.The laser soldering joint can be divided into three zones: stainless steel base metal zone, soldering seam zone and stainless steel base metal zone. The boundary between the soldering seam zone and the base metal zone is clear and distinct, and the microstructure of the joint is continuous without blowhole, crack or other defects. The microstructure of the soldering joint is mainly composed of black solid solution phase, big rhombic block white phase and short stick white phase. The joint consisted of α-Sn composite phase, SbSn phase and Cu₆Sn₅ phase. The diffusion layer of FeSn₂ metal compound is formed between the filler metal and the base metal with a thickness of 1 − 2 μm. Test results show that the shearing property of joint is about 39 MPa, which can meet the requirement of overlap joint of 304 stainless steel sheet.