Temperature-Dependent Selective Oxidation Behavior of Al₂Au Alloy: Insights for Tailoring Au-Enhanced Oxide Layers

Selective oxidation is a common strategy for enhancing protective oxide layers on an alloy. In this work, oxide films were obtained on Al2Au under a series of temperatures, and the structure, chemical state, and corrosion resistance were investigated. The oxidation behavior was confirmed to be temperature-dependent, exhibiting two distinct kinds of oxide films. Uniform oxidation occurred below the critical temperature Ts (700 < Ts < 800 °C), resulting in ultrathin oxide layers (<10 nm) with corrosion resistance enhanced by Au solute atoms. Phase-separate oxidation, occurring at temperatures above Ts, resulted in a much thicker oxide-affected region (250–300 nm) composed of Al2O3 and AlAu phases. Above 625 °C, bulk recrystallization led to Al diffusion through grain boundaries, disrupting the continuity of the oxide layer on the surface. These findings help further improve the existing alloy oxidation theory and develop potential surface modification methods on precious-metal-based alloys.