Influence of heat treatment on corrosion resistance of AlCoCrFeNi2.1 high-entropy alloy in 3.5 wt% NaCl solution

In this work, the effect of heat treatment with different cooling methods on the corrosion properties of the AlCoCrFeNi2.1 high-entropy alloy (HEA) is investigated. The AlCoCrFeNi2.1 HEA was prepared by vacuum induction melting. The AlCoCrFeNi2.1 HEA underwent heat treatment at 650 degrees C for 2 h, followed by various cooling methods: air cooling (HEA-AC), furnace cooling (HEA-FC), and water quenching (HEA-WQ). The microstructural characteristics and electrochemical corrosion behavior in 3.5 wt% NaCl solution were analyzed in detail. The results show that after different vacuum heat treatments, the phase composition of AlCoCrFeNi2.1 HEA remains unchanged, and the elemental composition of each phase is essentially the same, while the phase content varies, the FCC phase content is reduced, the BCC phase content is increased, and the hardness is increased after heat treatment. The average grain size decreases, with the order being: HEA-AC (68.82 mu m) < HEA-FC (88.45 mu m) < HEA-WQ (112.06 mu m) < HEA (145.40 mu m). After heat treatment, the corrosion resistance of HEA is improved. The HEA-WQ has the highest open-circuit potential, the highest E-corr of -0.29 V (SCE), the lowest I-corr of 3.07 x 10(-7) A/cm(2), and the highest Rp of 3(.)78 x 10(8) Omega<middle dot>cm(2), suggesting that the HEA-WQ exhibits the best corrosion resistance, which is attributed to its smaller grain size that facilitates passivation and the dense passivation film. Based on the analysis of corrosion morphologies, a pronounced selective corrosion behavior is evident on the surface of the AlCoCrFeNi2.1 HEA, with the BCC phase being preferentially corroded.