Influences of 17-4PH Stainless Steel and α + β Titanium Alloy Powders for Corrosion Susceptibility on Friction Stir-Processed AA7075-T651 Aluminium Matrix Composites

Stainless steel (17-4PH) and α + β titanium alloy (Ti–6Al–2Sn–2Zr–2Mo–2Cr–0.25Si) powders have been known for their high strength with low density as well as promising mechanical properties and remarkable corrosion resistance. In view of this, a comparative performance assessment was carried out to evaluate their percentage inhibition performance efficiencies (%IPEs) on the friction stir-processed 7075-T651 aluminium matrix composites (AMC) reinforced with 17-4PH and Ti–6Al–2Sn–2Zr–2Mo–2Cr–0.25Si powders. The process parameters used were the plunge depth of 0.3 mm, processing speed of 20 mm/min, the tilt angle of 3°, the rotational speed of 1500 rpm and 100% inter-pass overlap with double passes. Corrosion study was carried out in a concentration of 3.5% NaCl medium at an ambient temperature of 25 °C using potentiodynamic polarization technique on AA7075-T651/17-4PH AMC and AA7075-T651/Ti–6Al–2Sn–2Zr–2Mo–2Cr–0.25Si AMC with reference to the processed and unprocessed base metal. It was revealed that the AA7075-T651/Ti–6Al–2Sn–2Zr–2Mo–2Cr–0.25Si AMC has higher %IPE of 98.26%, while AA7075-T651/17-4PH AMC exhibited %IPE of 90.57%. The corrosion rate was extraordinarily reduced from 5.0718 to 0.087675 mm/year using α + β titanium alloy powder as corrosion resistance while that of 17-4PH stainless steel reduced to 0.47744 mm/year. The polarization resistance was greatly high when inhibition α + β titanium alloy powder was used and found to be 2240.7 Ω as against 191.06 Ω when 17-4PH stainless steel was used as a corrosion barrier. The SEM images of the corroded samples revealed the presences of pits and intergranular corrosion attack with the trace of flakes on the surfaces.