Effect Of Surface Morphology And Microstructures Of Typical Light Alloys On Electronic Work Function

As a lightweight structural material, light alloy has been widely applied in various fields, especially in aerospace, due to its excellent properties, such as low density and high strength. With the continuous development of science and technology, the electron work function (EWF) is used to characterize the physical priperties of the alloy surface and is now arousing more and more interest of scholars. At present, many phenomena and behaviors of the alloy surface have been successfully analyzed by means of the EWF, but the detailed mechanisms affecting the electron work function of the alloy surface have been rarely reported.In this thesis, AZ31magnesium alloy and2198aluminum lithium alloy were chosen as the objects, and the effect of various factors on the EWF was investigated. These factors included the change of surface oxidation, relative humidity, surface morphology, annealing temperature and time, and so on.The results show that the EWF of the two alloys increased as a function of surface oxidation time, which was in that the vacuum potential of alloy surface enhanced due to the appearance of the electric dipole layer caused by surface oxidation. The increase of relative humidity in air enabled the alloy to adsorb water film, and inhibited the escape of electrons, resulting in the increase of the surface EWF. Meanwhile, the change of air’s dielectric constant affected the measurement of the surface EWF. The surface roughness also had an important effect on the change of the EWF. For the alloy surface after polishing and surface corrosion, the EWF increased as the surface roughness increased. Based on the principle of the scanning Kelvin probe, the surface roughness caused the spatial fluctuation of electrostatic potential and electrostatic field between the pin and the alloy surface. Electric potential and electric field intensity increased with the increase of roughness, resulting in the change of the EWF. A mathematical model was introduced to simulate the profile of a rough alloy surface to further explain the influence of the roughness on the EWF. In addition, the effect of the annealing temperature and time on the hardness and the internal Fermi level of the alloys were found. It was further discovered that the EWF of the alloys decreased with the increase of the hardness of the alloys, which was consistent with the theoretical results based on free volume model and structural relaxation.