Abstract: In this work, possible short-term thermal exposure oxidation in hot processing including semi-solid processing is focused. We aim to investigate the short-term oxidation behavior of a novel powder metallurgy Al_0.8Co_0.5Cr_1.5CuFeNi high entropy alloy (HEA) in high-temperature solid (1000-1100 °C) and semi-solid (1125-1225 °C) intervals. From 1000 to 1225 °C, mass gain increases from 0.31 to 0.45 mg cm^-2 after 60 min oxidation, presenting superior oxidation resistance in the semi-solid state compared with other semi-solid alloys. Equiaxed α-Al₂O₃ grains are the predominant component of oxide scales and no obvious internal oxidation layer occurs in both solid and semi-solid intervals. Al₂O₃ scale growth is predominantly determined by outward Al³⁺ diffusion. For solid oxidation, different scale formation kinetics occur on various phases and the BCC(B2) phase has faster scale formation kinetics. This is attributed to outward Al³⁺ diffusion rate differences in various component systems. During semi-solid oxidation, the increased degree of chaos and number of vacancies in the liquid phase provide a diffusion channel, leading to rapid Al₂O₃ formation. Oxidation resistance in the semi-solid state is attributed to dense Al₂O₃ scales formed through selective oxidation of Al.

Key words: High entropy alloy, Short-term oxidation, Semi-solid interval, Oxidation behavior, Oxidation resistance