Contrasting initial events of localized corrosion on surfaces of 2219-T42 and 6061-T6 aluminum alloys exposed in Caribbean seawater

暴露在加勒比海水中的2219-T42和6061-T6铝合金表面初始局部腐蚀行为的比较（英文）

Aluminum alloy samples, 6061-T6 and 2219-T42, were exposed to Caribbean seawater for 90 d. The fluctuations of open circuit potential, considered as electrochemical noise (EN), were used to characterize and compare initial pitting events, which appeared on their surfaces. EN analysis was carried out using the power spectral density (PSD) vs frequency. The decrease of the β exponent in PSD graphs indicated a release of spontaneous energy with the progress of pit formation in seawater. The fluctuations were associated with the breakdown and formation of new corrosion layers. The values of β exponent in PSD graphs suggest that corrosion process of AA2219-T42 alloy occurs as a persistent non-stationary process, the dynamics of which is controlled by fractional Brownian motion (fBm), while on AA6061-T6 alloy the corrosion process was dominated by stationary and weakly persistent features, with the contribution of fractional Gaussian noise (fGn). After the exposure in seawater, SEM-EDX analysis revealed insoluble intermetallic particles on the alloys, rich in Cu or Fe and irregularly distributed. The preferential dissolution of Mg and Al occurs from the S-phase (Al2CuMg) of AA2219-T42 alloy.

将6061-T6和2219-T42铝合金样品暴露在加勒比海水中90 d。将开路电位的波动作为电化学噪声(EN),用来表征和比较合金表面的初始点蚀行为。采用功率谱密度(PSD)与频率的关系图进行电化学噪声分析。PSD图中指数β的减小表明,随着海水中铝合金点蚀的进行,出现自发的能量释放。开路电位的波动与新腐蚀层的破裂和形成有关。PSD图中指数β的变化趋势表明,AA2219-T42铝合金的腐蚀过程是一个持续的非稳态过程,其动力学行为受分形布朗运动(fBm)控制;AA6061-T6铝合金的腐蚀过程则主要表现出稳态和弱持久性的特性,这是由于分形高斯噪声(fGn)的贡献。将合金暴露于海水中后进行扫描电镜-X射线能谱(SEM-EDX)分析,发现合金上存在富含Cu或Fe、不规则分布的不溶性金属间化合物颗粒。AA2219-T42合金中Mg和Al的优先溶解发生在S相(Al_2CuMg)。