Structure performance and diffusion mechanism of aluminum alloy heat pipe low-temperature diffusion brazing joints

Aerospace-grade aluminum heat pipe had a high requirement of superpower and high heat flux removal in assembly bonding. Traditional cementing method was difficult to meet the requirements because of short service lifetime and poor reliability. A connection method of metallic bonding at low temperature used for aluminum alloy heat pipe was studied. The 6061 aluminum was successfully bonded with a new kind of intermediary material. The microstructure and composition of the joints was analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that a new phase CuGa₂ was formed during the diffusion of the intermediary material Ga and Cu. The joints which were preserved under the temperature of 80°C and diffused for 5 h/10 h/20 h each were observed. It was found that with more diffusion time, Ga and Cu diffused more adequately, Ga and Cu remained in the middle layer were less, and the joint structure formed was more uniform and compact. The coefficient of interface heat transfer was tested and the results suggested that the metallic bonding had a high coefficient which was about 82362 W·(m²·K)^-1 and fully met the requirements of aerospace grade heat pipe's high-power and high heat flux removal. The heat resistance performance of the joint was also tested and the results indicated that the melting point of the joint microstructure was higher than 300°C and the joints showed no liquefaction and remelting phenomenon at the temperature of 300°C. Finally, through the analysis of the aluminum alloy low-temperature diffusion brazing process, the interlayer of the joints diffusion mechanism was discussed.