Tribological performance of AZ91D/HfCp magnesium composite prepared through stir-ultrasonic-squeeze casting technique

Abstract

The present work investigates the influence of hafnium carbide, an ultra-high temperature ceramic reinforcement on the dry sliding wear behaviour of AZ91D magnesium composite. AZ91D/5 wt.% hafnium carbide composite and AZ91D alloy were fabricated using stir-ultrasonic treatment-squeeze casting method followed by heat treatment (T6). Microstructure and intermetallic phase studies were performed using scanning electron microscopy and X-ray diffraction techniques. Density, porosity and hardness of the materials were determined. Wear tests at room temperature were conducted at various sliding speeds (0.25–1 m/s) and normal loads (12.5–50 N), using a pin-on-disc tribometer. The temperature of wear varied from 50–200 °C for high-temperature wear tests. Compared to alloy, the composite showed better wear performance under all test conditions. Increasing the normal load increased the wear rate of both materials, but the wear rate decreased with an increase in sliding speed. The friction at the sliding interface decreased with an increase in normal load and sliding speed. The mechanisms of wear for both materials were abrasion, delamination, and oxidation at room temperature. At high temperatures, there was a dramatic increase in the wear rate of the alloy at 150 °C, whereas the wear resistance of composites improved up to 150 °C due to the presence of small amounts of hafnium carbide ultra-high temperature ceramic reinforcement. Abrasion, oxidation, delamination, and plastic yield were the primary wear mechanisms at high temperatures.