Effect of annealing on interior Vickers hardness and surface work function of light alloys

With the change of external environment, how to clarify the corresponding change of the interior and surface properties as well as their relationship is of both fundamental and practical significance. In this study, the correlation between the interior Vickers hardness (HV) and surface work function (SWF) of Mg and Al alloys was investigated by annealing at different temperature. With the increase of annealing temperature, the contrary change trend of the HV and the SWF was found. For example, for Mg alloys, the HV gradually decreased from 131 kg mm⁻² to 52 kg mm⁻² with the increase of annealing temperature from 200 °C to 500 °C, accordingly, the SWF increased from 4.22 eV to 4.44 eV. It was in that the annealing process allowed the alloys deform easily, increasing their ductility and decreasing their hardness. After annealing the surface oxidation layers brought the stronger electrostatic interaction between the free electrons and surface electrostatic field, and limited the escape of free electrons from the Fermi level to the vacuum level, resulting in the increase of the SWF. Such a correlation between the SWF and the HV will be of much help to understand the inherent relations between the surface and interior properties of all kinds of materials. (paper)