Corrosion Characteristics of Al-B<sub>4</sub>C Metal Matrix Composites in Boric Acid Solution

The corrosion behavior of Al-B 4 C metal matrix composites in H 3 BO 3 solutions with different Cl - contents was investigated using potentiodynamic polarization and zero resistance ammetry techniques. Results show that the corrosion of Al-B 4 C composites in H 3 BO 3 solution increases with increasing B 4 C volume fraction in the composites. The main corrosion characteristic of Al-B 4 C composites in H 3 BO 3 solution is the galvanic corrosion between Al matrix and B 4 C particles. In the galvanic couple, B 4 C particle acts as cathode and Al matrix acts as anode. The cathodic reaction is hydrogen revolution reaction, which controls the corrosion mechanism of Al-B 4 C composites. Pitting is not observed on the composite surface in the H 3 BO 3 solution with zero Cl - . However, with addition of Cl - in H 3 BO 3 solution, pitting occurs and the corrosion resistance remarkably decreases with increasing Cl - content. The corrosion resistance of Al-B 4 C composites in H 3 BO 3 solutions is compared with that in the standard 3.5% NaCl solution.