Abstract
A compocasting process including two steps, liquid and semisolid stirring. This process has been used to produce SiC particle reinforced aluminium matrix composites (A7475). In the presnt study, this process has been used to produce aluminium matrix composites reinforced with 15 and 25 vol.% SiC particles of 15, 30, 50 and 100 mum size. This process leads to complete wetting of SiC particles, good distribution in molten aluminium and it can be readily achieved at relatively low stirring rate. After casting, the composites were hot extruded, solution treatment at 753 K for 1.5 hours and ageing at 393 K for 6 hours (M). Then the interaction between SiCp and aluminium matrix has been studied. Al4C3 is not detected at the A7475/SiC interface due to lower processing temperature. The corrosion behaviour of extruded SiCp/(A7475) alloy and (A7475) were investigated under the condition of the peak aged (T6) in 3.5% NaCl using weight loss and a polarisation measurements. Some corrosion kinetic and mechanistic parameters have been studied such as anodic and cathodic Tafel slopes, corrosion potential and corrosion current density. The addition of SiC particle by 15 or 25 vol.% in aluminium alloy (A 74 75) decreases the resistance of these alloys to corrosion. The increase of particle size accelerates the corrosion process. Addition of Na2CrO4 as inhibitor to 3.5% NaCl decreases the corrosion rate of composites alloy. The inhibition efficiency was found to be increased with chromate concentration.