Aluminum-based Solder

Aluminum has a low melting point (660°C) and a very low vapor pressure (about 10-3Pa at 800C), so it is more suitable for use as a vacuum brazing filler metal. -The general aluminum-based brazing filler metal is Mainly based on the eutectic of aluminum and other alloying elements. As shown in Figure 1, aluminum and silicon can form a eutectic phase at 577°C. Therefore, most aluminum-based brazing filler metals used in vacuum brazing are composed of aluminum -silicon eutectic with a small amount of magnesium, which can improve the wetting performance. Because magnesium is an extremely strong activator, during the brazing process, the magnesium vapor can combine with the remaining oxygen in the brazing atmosphere or the oxygen in the water vapor to protect the parts from re-oxidation, and it may penetrate into the parts that have not been cleaned. Remove the oxide film. Aluminum-based brazing filler metals that do not contain magnesium are almost impossible to braze aluminum and aluminu m alloys in a vacuum.

Figure1 Aluminum and silicon eutectic phase

In order to further reduce the brazing temperature, the BAl55GeSi brazing filler metal can control the brazing temperature at about 550C, but the strength of the brazed joint obtained is very low, which is only suitable for use under static load conditions. In order to improve the strength of aluminum-silicon-magnesium brazing filler metal: BAl84SiCuMg, it can be used for brazing joints that require higher strength. At present, it has been successfully used for brazing of pure aluminum, partially forged aluminum and rust-proof aluminum.

Since the melting temperature of the existing aluminum-based brazing filler metal is mostly close to that of the aluminum alloy, strict requirements are put forward for the strict control of the brazing temperature during the brazing process. Therefore, the further development of aluminum-based brazing filler metals with excellent performance and lower melting temperature has become a key to promoting the vacuum brazing of aluminum and aluminum alloys.