Effect of Reinforcement Coating on the Oxidation Behavior of AA6061/SiC/20p Composite

Abstract

The oxidation behavior of SiO₂-active coatings on SiC reinforcement particles of an aluminium-matrix composite, AA6061/SiC/20p, was studied. In order to improve the processing behavior of the composites the SiC particles were coated prior to composite manufacture by a casting procedure, using the sol–gel technique. The oxidation resistance of the composites was analyzed to determine the influence of the manufacturing varibles. Gravimetric tests were used to evaluate the oxidation kinetics at 500°C. The nature of the corrosion products before and after accelerated testing was analyzed by Scanning-Electron Microscopy (SEM), EDX and low-angle X-ray Diffraction (XRD), to determine the influence of the oxidation environment on microstructural changes. Corrosion damage to the AA6061/SiC/20p composite was dependent on the manufacturing process and increased with the manufacturing temperature. Three corrosion products were detected γ −Al₂O₃, MgO and MgAl₂O₄. The corrosion resistance decreased slightly when the SiO₂ coating was used, and the matrix/SiC interfaces acted as preferential nucleation sites, but the intensity of the oxidation process was low. The use of active coatings on reinforcement particles is justified by the improvement in their wettability by molten aluminum, in spite of some slight loss of oxidation resistance