Abrasive wear of aged 2014 and 6061 aluminium alloy composites

Abstract

Al-based discontinuously reinforced metal-matrix composites (MMCs) have received attention because of their improved strength, high modulus and increased wear resistance compared with conventional A1 alloys. Although the specific strength of discontinuously reinforced MMCs is not as high as that of continuously reinforced composites, the isotropic properties and reasonable cost of discontinuously reinforced MMCs make them potentially useful wear-resistant materials. Intuitively, a harder matrix is expected to provide a better wear-resistant composite. Thus, hardness may be an important index in selecting the matrix alloy for wear resistance. It is generally believed that ageing treatment may be an effective way of improving the wear resistance of composites. Lin and Liu [1] showed that an overaged AI-Zn-Mg-SiC composite possessed the same wear resistance as the peak-aged composite. However, Ma et al. [2] suggested that the wear rate of the 6061 AI-SiC composite aged to peak hardness was the lowest; for the overaged composite the wear rate increased with decreasing hardness. This anomalous wear behaviour of different A1 alloy composites may be attributed to the difference in the chemical compositions of the A1 alloys. The main objective of this study was to compare the effects of ageing on the sliding abrasive wear behaviour of 2014 and 6061 A1 alloy composites. Composites containing 10 vol% silicon carbide particles (SiCp) with average particle size of about 20/zm were prepared by the powder metallurgy and hot-extrusion processes. For abrasive wear testing, cylindrical specimens 12.5 mm in diameter and approximately 10 mm high were machined. Solution-treatment was performed at 530 °C for 2 h, and the specimens were then water-quenched to room temperature. The ageing conditions were selected based on the variation of the matrix hardness relative to the ageing time, and included the as-solutionized, peak-aged (160 °C for 18 h) and overaged (160 °C for 120 h) conditions. The abrasive wear test was of the pin-on-disc type. Experiments were carried out under dry conditions by sliding the sample under an applied load of 10 N on a number 80 abrasive paper stuck to the grinding disc. Each test was conducted on a fresh abrasive paper. Wear losses were obtained by weighing the samples before and after the wear tests. The wear rate was calculated by converting the mass loss measurements to volume loss using the respective densities. The variations in hardness with ageing time of the 2014 and 6061 A1 alloy composites aged at 160 °C are