Effect of different heat treatments and varying volume fraction of nano-Al2O3 particles on the hardness and wear resistance of Al 7150 alloy matrix composite synthesized by hot uniaxial compaction technique

Abstract

The effect of three types of heat treatment and the addition of varying volume fraction of nano-Al2O3 particles on the hardness and wear resistance of Al 7150 alloy matrix composite produced by hot uniaxial compaction technique was investigated. Initially the Al 7150 alloy was synthesized from elemental powders (Al–88.265%, Cr–0.04%, Cu–2.3%, Fe–0.15%, Mg–2.35%, Mn–0.1%, Si–0.12%, Ti–0.06%, Zn–6.5%, Zr–0.115%) using planetary ball milling process. The Al 7150 alloy powders were later blended with varying volume fraction (0, 5, 10 and 15%) of nano-Al2O3 (40–50 nm) particles. The blended Al 7150 alloy composite powders were hot pressed at 400 °C. The compaction pressure was 500 MPa with a compaction time of 1 h before ejection. The hot compacted samples were later subjected to three types of heat treatment processes viz. T6, HTPP and RRA (retrogression and reaging). The microhardness (VHN) of the hot compacted samples increased with the increase in the addition of nano-ceramic particles. The VHN test results of the aged (T6, HTPP andRRA) samples showed higher hardness and the improvement in hardness was 44.11% for T6 sample when compared to the non-aged sample. XRD analysis revealed the occurrence of the stable MgZn2 precipitate phase, which played a significant role in the enhancement of its hardness and wear resistance. The wear behavior of the non-aged and aged samples was analyzed using a pin on disc wear testing machine. The wear test results demonstrated a tremendous enhancement of wear resistance of the T6 aged samples followed by RRA and HTPP treated samples compared to the non-aged samples. Wear surface morphology was studied using FESEM analysis to determine the wear mechanism.