Brazing of Aluminum Matrix Composites

(1) Brazing characteristics aluminum matrix composites mainly include particle (including whisker) reinforcement and fiber reinforcement. The materials used for reinforcement mainly include B, CB, SiC, etc.

When the aluminum matrix composites are brazed and heated, the matrix Al is easy to react with the reinforcing phase, such as the rapid diffusion of Si in the filler metal to the base metal and the formation of brittle dumping layer. Due to the large difference in linear expansion coefficient between Al and the reinforcing phase, improper brazing heating will cause thermal stress at the interface, which is easy to cause joint cracking. In addition, the wettability between the filler metal and the reinforcing phase is poor, so the brazing surface of the composite must be treated or activated filler metal should be used, and vacuum brazing should be used as far as possible.

(2) Brazing material and process B or SiC particle reinforced aluminum matrix composites can be brazed, and the surface treatment before welding can be done by sandpaper grinding, wire brush cleaning, alkali washing or electroless nickel plating (coating thickness 0.05mm). The filler metal is s-cd95ag, s-zn95al and s-cd83zn, which are heated by soft oxyacetylene flame. In addition, high joint strength can be obtained by scraping brazing with s-zn95al solder.

Vacuum brazing can be used for the connection of Short Fiber Reinforced 6061 aluminum matrix composites. Before brazing, the surface shall be ground with 800 abrasive paper after grinding, and then brazed in the furnace after ultrasonic cleaning in acetone. Al Si brazing filler metal is mainly used. In order to prevent the diffusion of Si into the base metal, a layer of pure aluminum foil barrier layer can be coated on the brazing surface of the composite material, or b-al64simgbi (11.65i-15mg-0.5bi) brazing filler metal with lower brazing strength can be selected. The melting temperature range of the brazing filler metal is 554 ~ 572 ℃, the brazing temperature can be 580 ~ 590 ℃, the brazing time is 5min, and the shear strength of the joint is greater than 80mpa

For graphite particle reinforced aluminum matrix composites, brazing in protective atmosphere furnace is the most successful method at present. In order to improve the wettability, Al Si solder containing Mg must be used.

As with aluminum vacuum brazing, the wettability of aluminum matrix composites can be significantly improved by introducing mg vapor or Ti suction and adding a certain amount of Mg.

Post time: Jun-13-2022