Study On Electrochemical Corrosion Resistance Of AZ31 Alloy By Al Ions Implantation

Electrochemical corrosion resistance of AZ31 alloy unimplanted and implanted with Al ions was evaluated by using anodic polarization measurement and electrochemical impedance spectroscopy(EIS). The results of anodic polarization indicated that magnesium alloy AZ31 dissolves as an anodic electrode in the solutions with Cl^-, and corrosion rates of AZ31 alloy decrease with increasing the Cl^-concentrations. Anodic dissolution of AZ31 alloy for pH<10.5 and passivating for pH≥ 10.5 are detected, respectively. In the solutions of 0.01⁰.08 N NaCl with pH=12, AZ31 alloy is passivated firstly and then broken down, pitting corrosion potentials decrease with the Cl" concentrations increase. EIS of AZ31 alloy suggested that the capacitance arc of EIS at high frequency accounts for hydrogen evolution of electrode at the cathodic polarization potentials. But at corrosion potential and anodic polarization potentials, EIS makes up of capacitance arc at high frequency and inductance arc at low frequency. The later shows the middle corrosion production of Mg⁺ in the electrode reaction. The metal dissolutions in magnesium alloy were carried out in the anodic polarization process at the same time.Al-ion implantation of AZ31 alloy is carried out in MEVVA ions source at room temperature and at elevated temperature. The ions implantation doses are 2 × 10¹⁶, 6 × 10¹⁶ and 1×10¹⁷ ions/cm², respectively. Preciption of the intermetallic phases from the magnesium alloy is related to the Al-implantation doses and the temperatures by using XRD analysis. The γ-Al₁₂Mg₁₇ phase is precipited out for Al-implanted AZ31 alloy at room temperature and 200 ℃ when the implantation dose is 1×10¹⁷ ions/cm², and at 350 ℃ for all the three doses. But Al₃Mg₂ phases are from Al-implanted magnesium alloy at room temperature for the dose of 1×10¹⁷ ions/cm². Corrosion potentials E_corr and pitting corrosion potentials E_b for Al-implanted AZ31 are increased, and corrosion currents I_corr and passivated currents I_p are decreased, so the pitting corrosion resistance of magnesium alloy AZ31 is improved in the solution with Cl" for Al-ion imaplantation at room temperature and elevated temperatures, and AZ31 alloy annealed after implanting Al. The corrosion resistance for Al-implanted AZ31 alloy is influenced by thecomposion of Al, phase contents and states in the surface. The corrosion resistance of AZ31 alloy implanted Al is decreased in the case of y phase precipition. In 0.08 N NaCl solution with pH=12, the corrosion resistance for Al-implanted AZ31 alloy is mainly influenced by the composion of Al. In 0.01 N NaCl solution with pH=12, Al ions implantation dose of 6X1016 ions/cm2 at 350 °C is the optimum modification process for AZ31 alloy to improve corrosion resistance, whose corrosion potential Eccr, pitting corrosion potential Eb, corrosion current Ion- and passivated current Ip were -1200 mV, -970 mV, 0.060 uA/cm2 and 0.001 mA/cm2, respectivelyc...