The influence of mechanical grinding on the microstructure and corrosion behaviour of A356 aluminium alloys

In the automotive industry, mechanical grinding is employed at finishing line rectification to remove defects left over from upstream, which may also result in microstructure modification within the near-surface region of the work piece and, consequently, affects its corrosion performance. The present work investigates the influence of mechanical grinding on the microstructure modification and corrosion behaviour of Al-Si-Mg (A356) alloy castings in order to advance the understanding of potential corrosion issues. It is found that a near-surface deformed layer with a maximum thickness of 3 mu m, characterised by ultrafine equiaxed grains of 50-150 nm diameter, is introduced by the grinding process on alpha-aluminium matrix. The near-surface deformed layer has a significant impact on the corrosion behaviour of the alloy; specifically, preferential dissolution of the near-surface deformed layer occurs when exposed to NaCl solution, together with trenching of the aluminium matrix around the eutectic silicon particles.