Heat Treatment Effect in the Corrosion Resistance of the Al-Co-Mn Alloys Immersed in 3 M KOH

Al-based alloys named M1, M2, M3, M4, and M5 doped with different atomic percentage (at%) of cobalt and manganese as cast and submitted at two heat treatments (600°C and 1100°C) were analyzed by using electrochemical techniques to evaluate their corrosion resistance immersed in 3 M KOH. With the heat treatments applied to the alloys, the sample M2 (65% Al, 20% Co, and 15% Mn) observed the highest corrosion resistance with $R_p$ values of $3.0\times {10}^2$ , $6.2\times {10}^2$ , and $1.61\times {10}^3\Omega ·\text{c}{\text{m}}^2$ as cast, 600°C, and 1100°C, respectively. The latter was in agreement with the $I_{\text{corr}}$ calculated from the polarization curves where the values decrease based on the heat treatment applied as follows: $1.60\times {10}^3>6.16\times {10}^2>3.07\times {10}^2\text{mA}/\text{c}{\text{m}}^2$ for 1100, 600, and as cast, respectively. Co concentration above 20% increases the corrosion current ( $I_{\text{corr}}$ ) and decreases the polarization resistance of the remain samples. The chemical analysis done with EDS and X-ray diffraction made confirmed the presence of compounds such as CoAl, Co2Al5, Co2Al9, MnAl4, and MnAl6.