Wettability of SnAgCu–Cr alloys on graphite with different Cr contents

Abstract

The wettability of brazing alloy on graphite surface is a key factor affecting the successful brazing of graphite to metals. By introducing active Cr, the traditional Sn0.3Ag0.7Cu brazing alloy can wet the graphite effectively. The design of active Cr introduction into SnAgCu alloy caused a significant decrease in contact angle, and the contact angle was decreased from 120° to 20° with the increasing content of active Cr. The influence of active Cr content on the wettability of SnAgCu/graphite system was investigated by sessile drop way at elevating and isothermal process in this work. Cr3C2 reaction layer formed at the interface of liquid alloy and graphite substrate, which enhanced the spreading of liquid brazing alloy and then decreased the contact angle. The thickness of Cr–C reaction layer kept identical of 2.5 μm with the further increasing content of active Cr. Finally, the wetting mechanism of SnAgCu–Cr/graphite system was proposed.