铝合金表面聚氨酯涂层在加速实验条件下的老化机制及规律研究

Assessment of Aging Performance of Polyurethane Coating for 7B04 Al-alloy with an Accelerated Testing Spectrum

针对有机涂层抗腐蚀性能评估问题,基于涂层老化物理机制,运用热力学理论建立了紫外线辐照条件下当量折算系数理论模型,提出了有机涂层加速老化实验谱编制方法。针对铝合金表面聚氨酯涂层进行了加速老化实验,分别从宏观和微观形貌、失光率、色差、粘附性能、电化学阻抗等多个方面表征了涂层老化规律,揭示了老化物理机制。结果表明,失光率和色差不能作为涂层失效评估参数,粘附性能和电化学阻抗能较好地表征涂层老化规律。涂层老化过程大致可以分成3个阶段,初期(第0~2个周期)抗腐蚀性能完好,低频电化学阻抗|Z|_(0.01 Hz)为10^(10)Ω·cm^2量级;中期(第3~7个周期),|Z|_(0.01Hz)为10~7~10~9Ω·cm^2量级,内部微孔增大增多,抗腐蚀性能明显衰减;后期(第8~9个周期),表面出现局部鼓包,|Z|0.01 Hz为106Ω·cm2量级,粘附性能仅为初始值的35%,涂层失效。涂层的使用寿命大约为8 a,这与实际使用情况相吻合,初步验证了涂层加速实验谱编制方法的合理性和可行性。

A model of equivalent conversion coefficient for UV radiation was firstly proposed, and which then was coupled with the existed acceleration corrosion testing method to establish a test spectrum for the assessment of aging performance of polyurethane coating on 7 B04 Al-alloy plate. The aging behavior of polyurethane coating were characterized by means of macroscopic-and microscopic-observation, gloss loss-, color change-and adhesion strength-measurement, and electrochemical impedance spectroscopy（EIS） etc. Results show that the gloss loss and color change are not the suitable index for representing coating degradation degree, but the adhesive force and EIS are the appropriate ones to characterize the aging behavior of coating. The aging process of coating can be broadly divided into three stages： in the initial stage, the coating was intact with impedance above 10^10Ω·cm^2; in the middle stage, the anticorrosion performance of the coating was impaired to a certain extent with impedance within a range of 10^7~10^9Ω·cm^2, while pores increase in the coating; and in the late stage, coating was failed with blisters on its surface, while, of which the impedance lowered to 10^6Ω·cm^2 and the adhesive was reduced to 35% of the original value. It was found that the coating service life was ca 8 a, which is in line with the behavior conditions of the coating at the local airport. On this account, the rationality and feasibility coating accelerated aging test spectrum were verified.