As we all know, anodized aluminum alloy film can significantly improve the surface properties of aluminum alloys, especially the surface hardness, corrosion resistance, wear resistance and other important performance related to the service life, so people describe the anodized film as aluminum alloy Functional "surface strengthening treatment means.
From the simple small-scale horizontal anodic oxidation production line with annual output of 3,000 tons imported from 20 years ago to the current production of large-scale vertical anodic oxidation lines with an annual output of 30,000 tons or more, its rapid development is evident. After continuous elimination, selection, integration and improvement, at present, China's aluminum alloy building profiles have formed a series of three surface treatment technologies, namely anodizing, anodized electrophoretic coating and organic polymer electrostatic spraying technology, and its development direction and level are Synchronized with international development, the equipment level, process characteristics and product quality have reached the international advanced level. As early as the mid-1980s, China's aluminum industry was in its infancy.
In 1986, the China Nonferrous Metals Corporation’s Science and Technology Bureau drafted a document on the performance testing methods and indicators for aluminum profile anodized films according to the opinions of some experts. At that time, it played a role in regulating product quality and promoting the development of production. Good effect. The document proposes the detection of six properties: (1) appearance color difference; (2) oxide film thickness; (3) plugging quality; (4) salt spray corrosion resistance; (5) abrasion resistance and (6) light resistance ( Color fastness). Due to the limitations of technology and equipment at the time, only specific requirements were put forward for the first three tests. Corrosion resistance, wear resistance, and light resistance are merely a concept. Specific performance test methods and test parameters, as well as performance acceptance criteria, are not specified. At present, the content of this document may not be perfect enough, but it has been clearly stated 20 years ago that the thickness of the anodized film and the quality of the sealing pores are fundamental properties that are essential, that is, the so-called properties of the anodized film. Must-test items.
In the past 20 years, the aluminum industry in China has developed rapidly. The technical requirements for the corresponding anodic oxide films, acceptance criteria and detection methods are relatively clear. The corresponding national standards have been improved and improved, and are basically in line with the standards of the advanced industrial countries. Therefore, the current performance testing items and detection methods should have newer and more content, so that they can keep up with the pace of development in China's production, and can more fully and systematically integrate with the international advanced technology and international standards.
The China Non-Ferrous Metals Standardization Committee organized and arranged a series of performance testing tests in 2004, the National and South China Nonferrous Metals Quality Supervision and Inspection Center, and six companies including Jianmei, Nanping, Xingfa, and Haofa, for the regular production of factories instead of The specially arranged products participated in the full test of this performance test and obtained a large number of nearly 20,000 data. The experimental results have been compiled by the National Non-Ferrous Metals Standardization Committee. Although China's product quality varies from country to country, overall it has greatly improved. The test data shows that the above-mentioned factory products are not inferior to the international advanced level, so we can proudly say that China's aluminum building profile industry is not only a big country, but also a real power. Film thickness uniformity and sealing quality The thickness of the anodized film is one of the more important performance indicators. It may be a symbolic data of the service life. The quality of the sealing hole is an important indicator reflecting the corrosion resistance of the oxide film. Tests have shown that the data changes in the phosphochromic acid weight loss test are in the range of 6% to 15%, or that the phosphochromic acid corrosion weight loss data deviation remains within 15%, which can be regarded as an acceptable measurement error. The new standard 8013.1 to be promulgated stipulates that the quality of the anodized film sealing of aluminum alloy building profiles and the nitric acid presoaking phosphorous chromic acid test is an arbitration test, which is the European standard EN12373.6:1999.
The experimental data shows that the sample with poor sealing quality has a greater “weightlessness increase†effect of nitric acid pre-soaking. Therefore, nitric acid pre-soaking is more sensitive to the identification and screening of the quality of the sealing quality of the weight loss indicator of phosphoric acid and chromic acid. Cold post-sealing post-treatment can significantly improve the sealing quality and speed up the sealing time. Tests show that if cold post-sealing post-treatment (ie, impregnation with pure water at 60-80°C for 10 minutes), the aging time can be shortened and the qualified quality of the sealing hole can be quickly achieved.
Other tests at home and abroad have also proved that the post-treatment of cold-sealed holes can significantly improve the plasticity of the cold-sealed anodic oxide film to suit the subsequent mechanical deformation without cracking. Corrosion Resistance and Weather Resistance The CASS test of anodized films is a routine test method for resistance to salt spray corrosion. Tests have shown that the CASS test of the anodized film is not fully compatible with the result of the plugging quality because the quality of the plugging represents the average corrosion rate, while the CASS test reflects the results of the localized corrosion. Especially for the anodic oxide film on the mechanical sandblasting surface, even if the quality of the sealing hole is acceptable, the CASS test cannot be performed. The CASS test of the same sample and the rating of the caustic wash will be one to two levels lower than the corrosion rating of the same sample. . The microscopic appearance of the sandblasted sample may be due to the incompleteness of the anodized film at the part of the sandblasted pit, and the increased sensitivity to localized corrosion.
The anodic oxidation test method for anodic oxidation film needs to be improved. The deviation of the visual bubble occurrence discriminating end point specified by GB5237 is very large, it seems that it is not suitable to continue to adopt and should be modified. Even if the data obtained by the resistance measurement method in Japan is used in the future and the accuracy is improved by the “approach methodâ€, it is difficult to completely correspond to the results of the drop alkali test and the results of the phosphoric acid chromatographic plugging quality test or the CASS test. Since the anodic oxidation test of the anodic oxide film is only found in the Japanese standard, both the international standard and the European standard do not have this method, so the necessity of the dripping test is still questionable.
Coloring of anodized film weather resistance. Electrolytic coloring of anodized bronze film, the test shows that the color difference data after ultraviolet radiation can be maintained at ΔE <2.6, it can meet the requirements of the national standard ΔE <3.0. Since there are relatively few participating units and data provided in this experiment, the confidence in data credibility and representativeness is relatively small, and it is advisable to continue to expand and in-depth experiments. In view of the Sino-Japanese experiments in the anodization and electrophoretic coating of composite membranes, Japan suggests that a joint test of weatherability and corrosion resistance and a joint test of colored anodized films be considered worthy of consideration.
Abrasion resistance of anodic oxide film At present, the use of sand falling method to test the wear resistance of anodic oxide film is basically adopted in China. However, the data is relatively dispersed. Many units believe that the wear coefficient of the anodic oxide film can exceed the index specified by the national standard well below 300 g/μm. Because of the falling sand test results and the environmental factors of the test process, the shape of the sand, the number of times the use of sand and other factors. For example, a factory measures the wear coefficient of an anodic oxidation film, and the wear coefficient of silvery white anodic oxide film is 1107 g/μm and 894 g/μm, and the corresponding values ​​of Japanese sand are 517 g/μm and 567 g/μm. The worn coefficient of the bronze anodized film was 1541 g/μm and 1423 g/μm, while the corresponding values ​​of the Japanese sand were 911 g/μm and 697 g/μm, which were almost one time different. The national standard stipulates that the abrasion resistance of the sand falling method can be completed with a wear factor of <300 g/μm. Most of the unit data indicate that all the data are >300 g/μm, and the AA20 sample is generally better than the sample. Samples of AA15.
The test parameters of jet mill method are more stringent. At present, it is only used by the National Nonferrous Metal Supervision and Inspection Center of Beijing. The dispersion of its test data is relatively large, and it is lack of comparison and verification of the data of other units in the country. Therefore, further improvement of equipment is needed to strive for more. More units can participate in the test work before they can make correct judgments. Since the jet mill method has national, international, and European standards, and the falling sand method has the Japanese standard, the extensive construction of jet mill equipment and methods is of great practical significance, and the test time can be shortened.
Atmospheric corrosion exposure results (the results of the UK 16-year test) The atmospheric exposure data of the anodized film is more basic than the corrosion data, and the credibility of various rapid corrosion detection methods should, in principle, have a correspondence to atmospheric exposure data. Sex. Although China has conducted tests of commonly used metals for nearly 20 years at atmospheric corrosion test stations, no complete data on green anodized films has been published yet. According to a report published by Barry R.Ellard, for 6063TF aluminum alloy, the anodizing conditions are: 150-165g/L sulfuric acid, current density: 1.4A/dm2, oxidation temperature: 20-21°C, the thickness of the anodized film is 15-40μm .
Barry summarized the experimental results of various types of atmospheric corrosion stations in the United Kingdom in the past 16 years. These data can be used as a reference for future summary of atmospheric corrosion exposure tests in China. Given that atmospheric corrosion exposure tests take a long time, and the reproducibility of data is not particularly satisfactory, especially the extent of pollution of the environment, the British data, although significant, can only have reference value. In the actual use of these data, you can only choose a larger factor of insurance to be considered, or that should choose the point of corrosion of the lower level or greater loss of film thickness as a basis for more reliable data. The data shows that the different degrees of corrosion of different test stations for the point of corrosion, proved that different levels of atmospheric pollution on the anodic oxide film, a large impact on the level of corrosion. In rural areas, oceans and lightly polluted atmospheres, no point corrosion occurred in the film thickness from 15 to 40 μm. However, heavy pollution of the industrial atmosphere can only reach a grade of 9 when the film thickness reaches 35 μm or more. The remaining film thicknesses are severely corroded. , film thickness 15μm sample is only 7 grades. Tests in the United Kingdom have shown that the marine atmosphere is not a harsher test condition. For this reason, despite the fact that the international standard stipulates that the United States’ Florida test is a prescribed place for atmospheric corrosion, it does not actually represent all atmospheric corrosion situations. Strictly speaking, It should be more reliable to use experimental data obtained from test stations with similar environmental conditions.