Abstract: Diffusion bonding of TC4 and QAL1031.5 was carried out under the condition of 850 ℃, 8 MPa and 30 min, but there are cracks existing on local area of diffusion zone. Microstructure of diffusion zone was analyzed using scanning electron microscopy (SEM), and diffusion distance and concentration distribution of elements were analyzed using EDS. The result shows that the transition zone thickness is 10 μm. Diffusion distance of element increases with increasing bonding time followed a parabolic law: x2=Kp(t-t0), and phenomenon of transition zone moving to TC4 are observed which is so called kirkendall effect . The occurrence of the cracks on the diffusion zone was studied in the theory of interfrcial pore and the reason for microcracks produced and improvement methods are found out. Thus, approving diffusion joint is attained by improving the welding process.

Key words: materials synthesis and processing technology, diffusion bonding, crack, microstructure, copper alloy, titanium alloy