Understanding the role of alloyed Ni and Cu on improving corrosion resistance of low alloy steel in the simulated Beishan groundwater

•The addition of Ni and Cu elements significantly inhibited the cathodic and anodic processes of steel corrosion.•Ni and Cu alloy elements were obviously enriched in the inner rust layer, which could improve the compactness of rust layer.•Fe6(OH)12SO4 stably existed in the corrosion products of NiCu steel because Ni(Ⅱ) or Cu(Ⅱ) could substitute Fe(Ⅱ) of Fe6(OH)12SO4 and increase its oxidation resistance.•Ni and Cu made Fe3O4 ionic selective by doping, which could repel the aggressive anions and improve the corrosion resistance.