Natural dealloying of brass driven by dezincification under low-pressure oxidation

In this study, the oxidation behavior and pore formation of C26000 (Cu–30Zn) and C27000 brasses were investigated under air at atmospheric pressure and reduced pressure. Specimens were heat-treated at 500 to 700 °C for 24 h, and the resulting oxide scales and subsurface microstructures were examined. Under atmospheric pressure, anisotropic ZnO growth accompanied rapid outward Zn diffusion and promoted localized Zn depletion, leading to deep elongated pores exceeding 10 µm in some cases. After oxide removal by hydrochloric acid, cross-sectional compositional profiles revealed a porous, Cu-rich sub-surface region (nearly pure Cu) extending to approximately 0.3 µm from the pore bottom, this region is situated beneath a top layer of ZnO film, providing direct evidence that pore formation originates from oxidation-driven dealloying through Zn depletion. Increasing the oxidation temperature resulted in smaller and more uniformly distributed pores. By comparison, oxidation under reduced pressure suppressed long-range pore coalescence and produced isolated, fine pores, because oxygen-limited oxide growth weakened reaction-driven Zn outward transport. • Natural dealloying occurred via dezincification, producing a Zn-depleted surface. • Surface porosity on brass was achieved through natural dealloying. • High-temperature oxidation produced uniformly distributed pores on the brass surface. • Low-pressure air oxidation formed a denser oxide layer and suppressed long-range pore coalescence.