Effect of Si/Mg molar ratio on the electrochemical behavior of Al/SiCP composites with bimodal distribution of reinforcements

The effect of the Si/Mg molar ratio - in the raw aluminum alloy - on the electrochemical behavior of Al/SiCP composites was investigated. Composites were fabricated by reactive infiltration of porous preforms with 0.6 volume fraction of silica-coated SiC with particle sizes of 10 and 146 gm, in the particle size ratio 1:5, correspondingly. Four experimental Al-Mg-Si alloys with Si/Mg molar ratios of 0.12, 0.49, 0.89, and 1.05, were used to infiltrate the preforms in argon followed by nitrogen, at 1100 degrees C for 60 min. The composites were characterized by Xray diffraction (XRD) and scanning electron microscopy (SEM) before and after electrochemical tests, measuring the corrosion potential (E-corr) and cyclic polarization in aerated and de-aerated 0.1M NaCl solutions, respectively. Results show that pitting potential (E-pit) becomes less negative with decrease in the Si/Mg molar ratio, thus enhancing the corrosion resistance. By contrast, E-corr tends to similar values after two hours of immersion.