Interfacial wetting and reacting between pyrolytic graphite and Sn–Ag–Cu–Al alloy under ultrasonication at a low temperature

Poor wetting and bonding serve as significant challenges in the joining of carbon materials at low temperatures. In this work, the ultrasonically assisted hot dipping of pyrolytic graphite was investigated in a SnAgCu–2Al liquid metal at a low temperature of 250 °C in air. During the ultrasonic-assisted hot-dipping process, the filler metal filled into the surface grooves of pyrolytic graphite. A closely contacting interface formed between the pyrolytic graphite and the filler metal. Interlayer penetration induced by the cavitation effect, and the amount and depth of penetration increased with ultrasonication time. A transition layer of Al₂O₃ was formed at the interface between pyrolytic graphite and the filler metal. Large amounts of O atoms were induced at the interface during the ultrasonically assisted hot-dipping process, and the reaction of Al and O preferentially occurred between the liquid metal and solid C. This was consistent with the thermodynamic calculation results. The joining of metallizing-pyrolytic graphite was achieved by soldering at same temperature of 250 °C in air, where the highest joint strength could reach 17.52 MPa, achieving a joining module with a high thermal conductivity of 392 W/(m·K) and reaching 90 % of the base material.