An Investigation of T6 Heat Treatment, and Corrosion Behaviour of AA7085/TiB2 Composites

There is potential to improve corrosion resistance of AA7085 aluminium alloy by adding ultra-high temperature ceramic particles such as TiB2 and by using better T6 ageing conditions. AA7085 composites with 3–9 wt.% TiB2 particles were fabricated by the stir-casting method. T6 heat treatment of 525 °C solutionising, then artificial ageing at 230 °C for 10 hours was performed. Hardness assessment, 3.5 wt.% NaCl immersion corrosion for 24 hours, 48 hours and 72 hours, and Optical microscopy and SEM analysis studies as indicates the fine distribution of TiB2 particles. The AT9 sample achieved a maximum hardness of 122 HV, about 35% higher than the base AA7085. The lowest corrosion rate was observed for the AT9 composite at 230 °C ageing rate of 0.12 mm yr-1 at 72 hours. TiB2 particles inhibited pit initiation and promoted the formation of an Al-rich passivation layer. At higher ageing, pitting was observed to increase due to the reduction of over-ageing precipitates. The AA7085 composite reinforced with 9 wt.% TiB2 and artificially aged at 230 °C improved the corrosion resisting behaviour. The TiB2-Al matrix interface and the formation of a dense passivation layer are the key mechanisms for the enhanced corrosion resistance process.