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• B2 phases in Al 0.3 CoCrFeNi HEAs are purposely controlled by annealing treatment. • Effect of B2 phases on corrosion resistance of Al 0.3 CoCrFeNi HEAs is studied. • The B2 phases deteriorate the pitting corrosion resistance of Al 0.3 CoCrFeNi HEAs. • B2 phases act as preferential pit nucleation sites and facilitate pit propagation. The corrosion resistance of Al-Co-Cr-Fe-Ni high entropy alloys (HEAs) is probably affected by B2 phases. In this paper, the effect of B2 phases on the corrosion behavior of Al 0.3 CoCrFeNi HEAs in 3.5 wt% NaCl solution is clarified in this paper by purposely controlling the formation of B2 phases using annealing treatment. The microstructure characterization reveals that the content of (Al, Ni)-rich and Cr-poor B2 phases increases and the electrochemical measurements show that the pitting corrosion resistance is deteriorated as the annealing temperature decreases. Accordingly, the B2 phase is confirmed to be detrimental to the corrosion resistance of Al 0.3 CoCrFeNi HEAs. It can be attributed to the preferential dissolution of B2 phases causing easier pit initiation, which is evidenced by the corrosion morphology observation and scanning Kelvin probe force microscopy measurements, and to the slower repassivation rate leading to easier pit propagation, as demonstrated by the quantitative analysis of potentiostatic polarization curves. [ABSTRACT FROM AUTHOR]