Abstract: For diffusion wleding of aluminum matrix composite Al₂O_3p/6061 Al, the micro-bonding behavior of weld zone between reinforcement and matrix (R-M), reinforcement and reinforcement (R-R) was investigated. The results showed that key processing parameters af-fecting the micro-bonding behavior in the weld zone was diffusion welding temperature, The micro-bonding of R-M and R-R was weak bonding when welding temperature was below the solidus of composites. Bonding of R-M was achieved when welding temperature was between liquidus and solidus of composites, then liquid matrix metal appeared on the bonding interface. At the same time, liquid metal infiltrated the bonding zone of R-R, and the contact of R-R transformed into the bonding of R-M-R, thus the joint strength was improved obviously.It was found that there was a "critical temperature" between the solid and liquidus temperature of composites.