Microstructure complexities of laser impact welded Al-Ti bonding interface

Laser impact welding (LIW) is a promising technique for thin film dissimilar materials solid state welding. The in-situ observation of this process is difficult due to its extreme short timeframe (∼1 μs) and high pressure (several GPa). This study revealed the microstructure complexities of the bonding interface at micro/nano-scale for the first time for LIW. Focused ion beam (FIB) and transmission electron microscopy (TEM) showed multiple structures along 5 μm long laser impact welded Al-Ti interface including smooth interface (length of 200 nm), intrusion structure (length of 800 nm), nanocrystal structure (diameter of 180 nm), diffusion structure (diffusion distance of 2 μm), and porous structure (pore size of 1–50 nm). The variety of the micro/nano scale microstructures reflected the uneven vertical impact pressure and horizontal frictional force. The findings revealed the multiplicity of the bonding mechanisms for LIW along the interface and help to precisely control the welding process.