Laser-implanted short fiber-like interface structure for strengthening welded-brazed joint of Al/steel dissimilar metals

The lamellar layer of intermetallic compounds (IMCs) was adversely affected the performance of welding-brazing joints in Al/steel dissimilar metals. In this study, a short fiber-like surface morphology was fabricated on the butt surface of Q235 steel via laser. The interaction behavior between the short fibers and the molten pool was captured using a high-speed camera. Laser-arc hybrid welding-brazing was then employed to join Al (6061-T6) to the steel. This process successfully created a short fiber-like interface structure at the joint. The relationship between microstructure and mechanical properties was investigated, compared with Al/bare steel (ABS) joint. The research results indicated that the IMCs layer consisted of FeAl₃ and Fe₂Al₅. The interface strength of the Al/short fiber-like surface structural steel (ASFSSS) joint reached 153.2 MPa, an 82.2% increase compared to the ABS joint, which reached 84.1 MPa. When the ASFSSS joints without the reinforcement were bent to 58.2° and 25.2° in the longitudinal and transverse direction, respectively, they remained intact. However, cracks were discovered when the bending angle of the ABS reached 39.1° and 0° in the two directions. Numerical simulation revealed that the short fiber-like interface structure significantly reduced residual stress and improved the stress distribution in the weld, thereby enhancing the strength and toughness of Al/steel dissimilar joints. The crack propagation path in the ASFSSS joint was deflected into the weld when it encountered short fibers, and the fracture morphology presented the characteristic of ductile-brittle mixed fracture.