Hardness Testing and Scratch Testing with Heat Treatment Time for Electroless Ni-P Plating on Aluminum Alloy Die Casting

Abstract

Electroless Ni-P plating is suitable for aluminum alloy die castings since the plating can be formed uniformly without being affected by the shape or the microstructure. Moreover, the hardness of the plating increases by heat treatment. In this study, the correlation between the hardness and the heat treatment time was investigated for the electroless Ni-P plating on the ADC12 substrate. The change in scratch characteristics was also examined with/without heat treatment of the plating. The samples were heat treated at 553 K~568 K for 0.9 ks~183.6 ks. Then, the samples were tested by Micro-Vickers hardness, scratch and indentation tests. The hardness of the plating reached its maximum value with the heat treatment time. The temperature dependency of the time to reach the maximum hardness was predicted by using Arrhenius type equation. When the plating reached maximum hardness, the hardness of the substrate was similar to that of as cast sample. However, the hardness of the substrate decreased with passage of the heat treatment time. In the scratch test and the indentation test, the plating was easily cracked with increasing in the hardness by the heat treatment. The critical load of the heat-treated samples also decreased in the scratch test. The results of these scratch test indicate that the hardening heat treatment of the plating does not necessarily have a positive effect on surface damage.