Analysis of the Surface-Preparation Effect on the Hardness-Measurement Uncertainty of Aluminium Alloys

Abstract

Surface roughness has a strong effect on the measurement uncertainty and scatter of results in instrumented indentation hardness testing. Thus, it is an important factor to take into account when planning experimental parameters. This research was focused on selecting the appropriate hardness method together with the surface preparation that would provide the best measurement accuracy. The material used for this investigation was a 2xxx-series aluminium alloy 2030 (AlCuMgPb) in the T6 condition, man- ufactured from one batch of homogenous material. The hardness measurements were performed using three different hardness methods: Brinell, Vickers and Rockwell. The analysis was first focused on the impact of the different surface-preparation parameters, performed on milled square blocks of aluminium alloy. The hardness tests were performed on samples with different surface preparations in which the surface milling parameters including rotation speed of the cutting mill, the feed rate and the depth of cut, were varied. Secondly, the impact of surface curvature was investigated by performing hardness measurements on cylinders with different diameters, manufactured from aluminium blocks. The statistical deviation of the obtained measurement results is graphically presented and discussed. Based on the obtained measurement-uncertainty results, it is concluded that the best measurement accuracy is achieved when the surface roughness is less than Sa < 0.6 μm and Sz < 10 μm for the Brinell and Rockwell tests, while the Vickers test requires additional grinding or polishing of the surface.