Enhancing the long-term anti-corrosion property of Mg alloy by quaternary phosphonium salt: Integrated experimental and theoretical approaches

[Display omitted] •Both [BPP][NTf2] and [OTP][NTf2] are efficient inhibitors for Mg Alloy in NaCl solution.•The inhibition efficiency is improved with the longer soaking time.•Corrosion resistance would be kept after 240 h immersion.•The inhibition mechanism is proposed by theoretical and XPS result. The corrosion resistance of two ionic liquids, [BPP][NTf2] and [OTP][NTf2], for Mg alloys is explored in NaCl solution by electrochemical approach, SEM, XRD, and XPS measurements along with theoretical calculations. The inhibition efficiency of [BPP][NTf2] is better than that of [OTP][NTf2] in three tested NaCl solution. Their inhibition performance is improved after long time immersion. Moreover, the [OTP][NTf2] would exceed [BPP][NTf2] after 96 h immersion. The essential item to affect the long-term inhibition performance is elucidated by the molecular dynamics simulations. The possible inhibition mechanism is proposed according to the XPS results along with the quantum chemical calculations.