时效对Al-2Li二元合金钝化膜耐蚀性及结构的影响

Influence of aging on corrosion resistance and structure of the passive film formed on Al-2Li binary alloys

Al-Li合金具有低密度、高强韧性和低的腐蚀疲劳扩展速率的优点,在航空领域有着广泛应用.Al3Li(δ′)相是Al-Li合金中主要强化相之一,因含有活性元素Li对该合金的腐蚀行为产生显著影响.为明确δ′相在Al-Li合金电化学腐蚀中的作用,真空熔炼制备Al-2Li二元合金,固溶后进行180℃等温时效,用X射线衍射(XRD)检测合金的相组成.在质量分数为3.5%的NaCl水溶液中,用动电位极化的方法测量了该合金的极化曲线.-0.85 V vs SCE钝化电位下形成钝化膜后,用电化学阻抗(EIS)检验钝化膜的耐蚀性;用恒电位阳极极化和Mott-Schottky(M-S)曲线对该合金钝化膜的结构进行分析.结果表明,Al-2Li合金的自腐蚀电位随时效时间增加先正移后负移;固溶和时效合金钝化膜的EIS都由两个容抗弧组成,时效未改变钝化膜的腐蚀机制;钝化膜耐蚀性由高到低的顺序为:时效20 h>固溶>时效40 h>时效1 h,且耐蚀性与其致密性及膜内的载流子密度有关.

Al-Li alloys have the advantage of low density, high strength and toughness, and low corrosion fatigue rate. This combination of properties has led to their use in aerospace. Al3 Li(δ′)phase is one of main strengthening phases of Al-Li alloys. The higher chemical reactivity of Li clearly influences its corrosion behavior. In order to explain the effect of δ′ phase in the Al-Li alloy electrochemical corrosion process, an Al-2 Li binary alloy was prepared by vacuum melting. Aging treatment of Al-2 Li alloy at 180 ℃followed by solution treatment were carried out. A potentiodynamic polarization plot of the alloy was tested in a 3.5%(mass fraction)NaCl solution. Phase composition of all samples was determined by X-ray diffraction(XRD). Passive film was formed on this alloy at a passivation potential of-0.85 V vs SCE. Corrosion resistance of the passive film on the surface of the Al-2 Li binary alloy was tested by electrochemical impedance spectroscopy(EIS). Structure of the passive film was analyzed by potentiostatic polarization and the Mott-Schottky(M-S) approach. Results show that the corrosion potentials of Al-2 Li alloy initially move toward the positive, then toward negative, along with increasing aging time. EIS spectra of the passive films on the solution treatment and aging have two capacitive impedance arcs;the corrosion mechanism is not changed by the aging treatment. Corrosion resistance of the passive film is, in order from high to low, aged 20 h > solution treatment > aged 40 h > aged 1 h, and is related to the compactness and acceptor concentration of the passive film.