Scratch and Wear Properties of Electroless Ni-P Plated Aluminum Alloy Die Casting in Surface Hardening Heat Treatment

Abstract

  In this study, changes in mechanical properties were characterized using scratch testing for electroless Ni-P plating on JIS ADC12 alloy die casting substrates with/without surface hardening heat treatment. The scratch tests were conducted at a progressive-force of 1N-70N for hardened plating with a hardness of 962HV and for as-plated plating with a hardness of 558HV. The hardened plating showed lower critical normal-force compared to the as-plated plating. Numerous cracks were found to occur easily in the scratch track of the hardened plating owing to embrittlement and lower plating’s flexibility for substrate deformation. These scratch characteristics indicate that hardened plating does not necessarily have a positive effect on surface damage. Based on the scratch test results, ball-on-disk wear tests were performed at various normal-forces of 5N, 9N, 15N and 20N respectively up to the wear distance of 500m. Changes in wear loss in relation to wear distance were also measured at the normal-force of 20N to investigate the progress of wear under high force conditions. Wear loss of the hardened plating was lower than that of the as-plated plating at the normal-forces of 5N and 9N. However, as the normal-force increased to 15N and 20N, the wear loss of the hardened plating overtook that of the as-plated plating. Plating fragments was observed to drop during the wear process of the hardened plating under high forces. Then, wear on substrate developed around the wear at a distance of 400m-500m, leading to significant increase in wear loss.