Interfacial microstructure characteristics and failure mechanism of the laser welding-brazing steel-Al joints with various welding parameters

Abstract

The microstructure details of the interface, mechanical properties and failure mechanism of laser welding-brazing (LWB) steel-Al joints with various welding parameters were comparatively investigated. The emergence of ternary Fe–Al–Si intermetallic compounds (IMCs) was observed in the interfacial area of the joints prepared utilizing ER4047 filler. In contrast, only the binary Fe–Al IMCs were formed in the interfacial area of the joints prepared employing ER5356 filler. With the same laser tilt angle, the IMCs layer of the joints prepared with ER4047 was thinner than that of the joints prepared with ER5356, implying the rapid growth of the IMCs welded via the ER5356 filler. The tensile strength exhibited by the former surpassed that of the latter. Employing the same filler metal, the average thickness of the IMCs layer of the joints with laser tilt angle of 10° was smaller than that of the joints with laser tilt angle of 20°. The strength of the joints with smaller tilt angle was better than that of the ones with bigger tilt angle. The tensile test outcomes revealed that there existed failure competition among the Al alloy base metal (Al-BM), weld metal (WM) and interface structure. If the interface structure was Fe–Al IMC with high brittleness, the cracks propagated along the interface, and finally fractured at the interface. If the interface structure was Fe–Al–Si IMC with good toughness, the crack propagation in the interface region could be hampered. In this case, the joint was prone to occur via WM failure or even Al-BM failure modes.

Keywords

• Steel-Al joint
• Welding parameter
• Failure mechanism
• Intermetallic compound