Characteristics Study On Laser Welding-Brazing Of Aluminum/Titanium Dissimilar Materials

A novel technology, laser welding-brazing, is available for the joining of dissimilar materials with large different physical properties. The joint has dual characteristics and can be divided into a welding part on the low melting point metal side and a brazing part on the high melting point metal side. Because there are two different bonding mechanisms, it's difficult to control energy input and interface reaction in laser welding-brazing process.Laser welding-brazing was conducted using AlSi₁₂ filler metal for Al/Ti dissimilar materials in this paper. Joint strength was measured by tensile test, and fracture mechanism was analyzed. The interface structure of Al/Ti joint was analyzed via SEM, EDS, XRD and optical microscopy. Furthermore, the interface brazing mechanism was obtained from interface structure analysis.The results show that energy input must be appropriately allocated for two different bonding mechanisms through laser spot offset for aluminum. The rectangular spot laser heating source with symmetrical energy distribution makes perfect surface quality of dual sides weld seam. The jagged interfacial layer forms between mixed seam and titanium, and has different configurations at different interface locations. The interfacial layer at top interface includes a dentate Ti₅Al₁₂Si₃ intermetallic compound layer and a continuous Ti₇Al₅Si₁₂, Ti₂₉Al₂₃ and Ti3Al hybrid layer nearby titanium.Three different fractures are found. Most joints are quasi-cleavage fracture in seam, the joint is cleavage fracture on brazing interface layer when energy input is excess, and the joint is intergranular fracture on welding fusion zone when energy input is optimum. Interface structure and bonding property are essential factors affecting fracture. Fracture often origins from bottom interface because the special structure of welding-brazing joint makes serious stress concentration. Fortunately, nail-connecting effect of interface reaction product improves interface bonding property and reinforces joint strength.Generally, the heating requirement for two different bonding mechanisms is easily achieved because of the precise heating characteristic of laser beam, and the thickness and distribution of intermetallic compound layer can be availably controlled in laser welding-brazing process.