Studies Of The Aging Behaviors Of High-Strength Aluminum Alloy Protective Coating In Typical Service Environment And Indoor Accelerated Environment And Their Correlation

Using organic coating is one of the most widely used means for preventing metallic materials from corrosion in industry as well as in high-speed trains.In recent years,the coating system on service could not met the need due to the rapid development of high-speed trains and the increasing train speed.Developing new nano-composite coatings can not only satisfy the demand of vehicles for environmental adaptability but also improve the train body's weather resistance in the hash and changing environment,delaying the corrosion of vehicles and increasing the service life.For organic coatings,the exposure test in natural environment can truly reflect the ageing-resistant performance of the protective coating in the typical climatic environment.However,the modern high-performance anti-corrosive coating system has limited degradation after exposure in the natural climate for several years,so predicting the service life of the new coatings by means of exposure test in natural environment is almost impossible to achieve.Therefore,the laboratory accelerated weathering test has become an important means to examine the performance of anti-corrosion coatings,which can simulate the situation about the aging of the coatings in a relatively short period.The correlation research is put forward with the development of the accelerated test,which mainly refers to the accelerated relationship between the natural environment exposure test and the corresponding laboratory accelerated weathering test.It is possible to simulate natural aging for years or even decades of coatings under laboratory conditions in a very short time by studying the correlation,which is important for testing coating quality,evaluating coating life and developing new coating systems.In this paper,a new nano-composite coating system on aluminum alloy used in high-speed trains was located in four typical climatic environmental areas(Beijing,Shenyang,Wuhan,and Guangzhou)for the natural environment exposure experiment.At the same time,a reasonable experimental program was designed for the laboratory accelerated weathering experiment.The actual aging behavior in four typical climatic environmental areas and the accelerated aging behavior in laboratory accelerated weathering experiments for the new nano-composite coating were analyzed,as well as the correlation between them,which can provide the theoretical basis for the research of anti-aging properties of coatings and forecast service conditions.The main conclusions of the experimental study are as follows:(1)In the most comprehensive view,for the experimental test pieces exposed to the natural environments at the four test sites,the aging of the specimens at Guangzhou is the most serious and the aging in Shenyang and Beijing is lighter,which means that the degree of aging about tested pieces is closely related with the intensity of illumination and the average temperature of the test areas.(2)The tested specimens exposed to the natural environments at the four sites all remained good corrosion resistance and the aging of the resin was not serious until the 24th month,which indicates that the nano-composite coating system has excellent aging resistance.(3)Among the accelerated aging methods employed in the indoor accelerated aging experiments,the xenon lamp aging test contributed most to the accelerated aging rate of coating surface.(4)The accelerated relationship between indoor and outdoor aging tests are as follows:From the surface morphology of view,the indoor accelerated aging test for a cycle is equivalent to the natural environment exposure test for 6 to 8 months;from the change of glossiness of view,the indoor accelerated aging test for a cycle is equivalent to the natural environment exposure test for 5 to 6 months;from the color difference value of view,indoor accelerated aging test for a cycle is equivalent to the natural environment exposure test for more than 10 months.(5)The change of the chemical bonds on the surface of the coating at both indoor and outdoor aging tests are not completely uniform.The aging mechanisms of the natural environment exposure test and the indoor accelerated aging test are not completely consistent.