Surface oxide development on aluminum alloy 6063 during heat treatment

Abstract

We report on the influence of oxygen partial pressure for the development of surface oxides covering the industrial aluminum alloy standard 6063 at temperatures ranging from room temperature to 500° C. Using an array of synchrotron‐based techniques, we followed the change in oxide thickness, chemical composition, and the lateral distribution of alloying elements. The impact of the oxygen chemical potential is most visible at high temperatures where the oxide composition changes from mostly Al based to mostly Mg based. This is in stark contrast to the ultra‐high vacuum (UHV) conditions where only a partial compositional transition is observed. The microscopy data demonstrate that in the UHV case, Mg segregation onto the surface occurs firstly at grain boundaries at 300° C and secondly at sites over the entire surface at 400° C. Further, the initial oxide thickness is 45 Å, as determined by XPS and XRR, decreases in all observed cases after heating to 300° C. At higher temperatures, however, the oxygen partial pressure highly influences the resulting oxide thickness as evident from our X‐ray reflectivity data.

Investigation of Oxide Thickness on Technical Aluminium Alloys—A Comparison of Characterization Methods

“…As known from the literature, the growth rate of aluminium oxide at ambient pressures and temperatures is initially extremely rapid and decreases with increasing thickness of the oxide. In general, the growth rate is positively influenced by increased temperatures to a certain point and elevated oxygen concentrations [25]. However, as soon as a so-called limiting thickness is reached, the oxide growth stops and does not change with time [26].…”