Role of the Size of Iron- and Silicon-Rich Particles in the Atmospheric Corrosion Performance of Al-Mg-Si Alloys

Abstract

Aluminum-magnesium-silicon (Al-Mg-Si) alloys are vital lightweight materials partly owing to their excellent corrosion properties. While there is a wealth of knowledge in the literature on effect of chemical composition of second phase particles and constituents on their anodic/cathodic activity, there is little known on the influence of particles’ size on the corrosion behavior of Al alloys. Using friction stir welding/processing (FSW/P), which was combined with quantitative microstructural analyses, we were able to clearly uncover this previously less-recognized effect of intermetallic particles in an extruded Al-Mg-Si alloy. The exposures were performed at ambient temperature and in the presence of 95% relative humidity (RH) and 400 ppm CO2 for a time interval of 200-3200 hours. Prior to the exposures, samples were contaminated with 200 μg/cm2 NaCl, mimicking the environment that exists in marine atmospheres. The results showed that the size of the particles in the alloy microstructure plays extremely important role in the overall corrosion performance of the processed/welded materials. Thus, it was demonstrated that the extent of corrosion attack in the heat affected zone (HAZ) of the welded/processed alloys directly depends on the size of particles in the processed regions (a macro-galvanic corrosion process). In addition, using local corrosion analysis, it was clearly noted that the cathodic activity of intermetallic particles in this family of Al alloys is size-dependent.