Scanning Kelvin Probe Force Microscopy and Density Functional Theory Studies on the Surface Potential of the Intermetallics in AA7075-T6 Alloys

Abstract

The surface potentials of Mg2Si and Al7Cu2Fe intermetallic particles in AA7075-T6 alloys were investigated by scanning Kelvin probe force microscopy (SKPFM) technique. The experimental surface potentials of Mg2Si and Al7Cu2Fe intermetallic particles relative to Al matrix were ranging from − 368 to − 265 mV and 480–500 mV, respectively. A theoretical method for assessing relative nobility of intermetallics in Al alloys was discussed through first principle calculation. The work functions and surface energies of Mg2Si and Al7Cu2Fe surfaces were calculated by using density functional theory (DFT) method. The results showed that work functions and surface energies of Mg2Si and Al7Cu2Fe intermetallics were influenced by the orientations of crystal face and terminal types. At the oxygen coverage of 1/4 ML and 1 ML, the theoretical surface potential differences between Mg2Si intermetallics and Al matrix were increased by 10–560 mV and 0–620 mV, while those between Al7Cu2Fe intermetallics and Al matrix were increased by 62–360 mV and 102–331 mV. For the adsorption of oxygen atom, theoretical surface potentials of Mg2Si and Al7Cu2Fe intermetallics relative to Al matrix had a close agreement with the experimental surface potentials. It was verified that DFT method was a valuable theoretical approach to assess the relative nobility of different phases in alloys.