Effect of Reinforcement Coating on Corrosion Behavior of AA6061/SiC/20p Composite in High Relative Humidity Environments

A study of the influence of silicon dioxide (SiO₂) active coatings on silicon carbide (SiC) reinforcement particles of an aluminum metal composite, AA6061 (UNS A96061)/SiC/20p (Al-Mg-Si alloy reinforced with 20 vol% of SiC particles), exposed to a high relative humidity environment (98% RH and 50°C), was carried out under simulation in a climatic chamber. To improve processibility, SiC particles were coated prior to composite manufacture by a casting procedure, using the sol-gel technique. The corrosion resistance of the composites was analyzed to determine the influence of the manufacturing variables. The nature of corrosion products before and after accelerated testing was analyzed by scanning electron microscopy (SEM) and low-angle x-ray diffraction (XRD), determining the influence of microstructural changes on corrosion behavior during exposure to the aggressive environment. The kinetics of the corrosion process was characterized on the basis of gravimetric tests. The corrosion damage to composite AA6061/SiC/ 20p was dependent on the manufacturing process. The detected corrosion product was basically bayerite (Al₂O₃·3H₂O). Corrosion resistance decreased with the use of the SiO₂ coating, and the matrix/SiCp interfaces acted as preferential nucleation sites, but the corrosion process was of low intensity. The use of active coatings on reinforcement particles is justified in that it demonstrably improves wettability by molten aluminum, despite some slight loss of corrosion resistance.