Aluminum anodic oxidation film performance analysis and quality evaluation

As is known to all, aluminum alloy anodic oxidation film can significantly improve the surface performance of aluminum alloy, especially the surface hardness, corrosion resistance and wear resistance is related to the service life of the important performance, so people will be anodized aluminium alloy described as "universal" surface strengthening processes.


Annual output of 3000 tons of imports from 20 years ago, a simple small horizontal anodic oxidation production line, so far more than the annual output of 30000 tons of large vertical anode oxidation line put into production, the rapid development of it.After selection, selection, integration and improve continuously, at present, our country architectural aluminum shaped to form the three major series of surface treatment technology, namely anodic oxidation, anodic oxidation electrophoresis coating and organic polymer electrostatic spraying technology, its development is synchronized with the international development direction and level, equipment level, process characteristics and product quality has reached the international advanced level.As early as the mid - 1980 - s, the aluminum industry in China in the period of germination.


In 1986 when China nonferrous metals corporation technology bureau, according to some experts timely drafted "about building aluminum anodic oxide film performance test methods and indexes" files, played the specification at the time the product quality and a great role to promote the development of production.This document recommends screening six performance: (1) the appearance of color difference;(2) the thickness of oxide film;(3) hole sealing quality;(4) salt fog corrosion resistance;(5) the abrasion resistance and light resistance (6) (color fastness).Due to the technical level and equipment constraints, only for the first 3 tests specific requirements are put forward.Corrosion resistance, abrasion resistance, light fastness is only put forward a concept of specific performance testing methods and testing parameters, and stipulates the performance indicators such as acceptance of all have no.So far, the contents of this file may not be enough, but before 20 years has clearly put forward the anode oxidation film thickness and hole sealing quality is the essential significance of the basic performance, namely the so-called shall belong to the properties of anodic oxide film project.

In 20 years the rapid development of aluminum industry in China, the corresponding requirement for performance of anodic oxide film, acceptance index and test methods and other technical content is clear, the corresponding national standard has been perfect and improve, with the advanced industrial countries standard basic standards.So now the performance of the test items and test methods should be updated and more content, to keep up with the pace of production in our country, and can be content with the international advanced technology level and international standards is more comprehensive and more systematic.


China nonferrous metals standardization committee in 2004, organize and arrange a series of performance tests, countries and south China quality supervision and inspection center, non-ferrous metal and jianmei, nanping, xingfa, MinFa six companies, such as the factory regular production rather than a special product, involved in the performance test of full-scale test and get a lot of close to 20000 data.The experimental results has been compiled by the national nonferrous metals standardization committee.Although the quality of the products in our country in terms of the country is different, but on the whole, had the very big enhancement.Test data show that the factory products as compared with the international advanced level, so you can proud to say that aluminum building material industry in China has not only is a big country, and become a real power.Film thickness uniformity and hole sealing quality of anode oxide film thickness is one of the most important performance indexes, is likely to be an iconic data, the service life of hole sealing quality is an important index of oxide film corrosion resistance.Test showed that the phosphorus chromate weightlessness experiment data changes, are in the range of 6% ~ 15% between, or phosphorus chromic acid corrosion weightlessness data deviation keep within 15%, can be seen as acceptable error of measurement.8013.1 the forthcoming new standard, aluminum alloy profile anodic oxidation film hole sealing quality construction, nitrate presoak phosphorus chromic acid test is arbitration test, this is the European standard EN12373.6:1999.

     Experimental data show that the hole sealing quality worse sample, nitrate presoak "weightlessness increase" effect, the greater the therefore presoak nitrate for phosphorus chromate weightlessness logo hole sealing quality identification and selection of qualified or not.Cold hole sealing post-processing can significantly improve the quality of hole sealing and speed up the hole sealing time.Tests show that if cold hole sealing post-processing (i.e., at 60 ~ 80 ℃ water immersion 10 min), can shorten the aging time quickly reach the hole sealing quality qualification level.Other domestic and foreign test also proved that the cold sealing hole post-processing can obviously improve the cold hole sealing anodic oxide film of plastic, in order to suit the subsequent mechanical deformation from cracking.Corrosion resistance and weather resistance of anodic oxide film CASS test is a normal test method of salt fog corrosion resistance.Experiment, the results showed that the anodic oxide film quality is not the result of the CASS test and hole sealing can completely, because the quality of hole sealing said the average corrosion rate, and CASS test reflect the results of the local corrosion.Especially for mechanical sanding the surface of the anode oxidation film, even though the hole sealing quality qualification, not by CASS test cases have occurred, the same sample of CASS test compared with alkaline cleaning rating, corrosion level will be low 1 to 2 levels.Sand blasting samples microstructure may be due to part of the sand pit in anodic oxide film is not complete, cause local corrosion sensitivity increase.


Anodic oxidation film of alkali test method to be improved.GB5237 rules of visual bubble happened discriminant end point error is large, seems to have not continue to use and should be amended.Even if the future Japanese resistance measurement method is used to get data, and using the approximation method to improve accuracy, drop test results and the phosphorus chromic acid alkali hole sealing quality test or CASS test results is also difficult to completely.In view of anodic oxide film drops of alkali test only in Japan's standards, international standards and European standards are not the way, so the necessity of drops of alkali test is still questionable.


Colouring anodized weatherability.Electrolytic coloring bronzing anodized, after uv radiation tests showed that the color difference data can keep the Δ E < 2.6, so we can meet the national standard of Δ E < 3.0.By participation units, and to provide data on this test is less, so the data reliability and representative is smaller, should continue to expand and further tests.Given that China and Japan in terms of anodic oxidation electrophoresis coating composite film of experiment, Japan suggest weather resistance and corrosion resistance of the joint test, the combination of colouring anodized test is necessary to consider.


The wear resistance of anodic oxide film at present domestic basically adopts the shakeout to test wear resistance of anodic oxide film, but the data is more dispersed, many units all think abrasion coefficient can be far more than China national standards < 300 g/index of microns.Because the shakeout method test results with the test process of environmental factors, the shape of the sand, sand factors such as the use of.Such as the determination of the abrasion coefficient of anodic oxide film in one power plant, silver anode oxidation film of home-made sand abrasion coefficient of 1107 g/u m and 894 g/u m, and the corresponding value of the sand is 517 g/mu m and 567 m g/mu.Tan anodic oxide film of home-made sand abrasion coefficient of 1541 g/u m and 1423 g/u m, and the corresponding value of the sand is 911 g/u m and 697 g/u m, almost doubled.Shakeout method of national standard of the criterion of wear resistance to abrasion coefficient < 300 g/mu m for qualified can be completed most of the unit of data show that all the data are > 300 g/mu m, which generally AA20 samples better than AA15 samples.


Spray equipment test parameters of the grinding is strict, only Beijing national non-ferrous metal using the supervision and inspection center, the test data of dispersion is larger, and the lack of other domestic unit data comparison, so still need further perfect equipment, strive for more units to participate in the test work, can make the right judgment.Due to the jet grinding with national standards, international standards and European standards, and shakeout legal system, the Japanese standard, thus widely construction of jet grinding equipment and the method is of great practical significance, at the same time can be shorten test time.

The results of atmospheric corrosion exposure (UK 16 years test results) atmospheric exposure of anodized data is the basis of corrosion data, fast corrosion testing methods of credibility, in principle, should have correspondence for atmospheric exposure data.Though our country has been in the atmospheric corrosion test station for nearly 20 years of commonly used test of metal, but has yet to complete the green anode oxidation film of published data.According to BarryR. Ellard report for tf 6063 aluminium alloy, anodic oxidation conditions as follows: 150 ~ 165 g/L sulfate, current density: 1.4 A/dm2, oxidation temperature: 20 ~ 21 ℃, anodic oxidation film thickness of 15 ~ 40 microns.Barry 16 years in the UK are summarized all kinds of atmospheric corrosion of the test results, the data can be used as the future of our country's exposure to atmospheric corrosion test results are summarized up.Given that exposure to atmospheric corrosion test time is very long, at the same time, data repeatability not ideal, especially environmental pollution degree is different, the data although very meaningful, also can have reference value.In the actual use of these data, can only choose larger insurance coefficient for consideration, or should have the option of corrosion level is low or film thickness loss larger data as a basis for more reliable.Data shows that different test station for the corrosion degree of difference is very big, to prove the degree of air pollution on the influence of anodic oxide film of corrosion level greatly.In rural areas, Marine and lightly polluted atmosphere, film thickness has not been from 15 to 40 microns point corrosion, and heavy pollution industry atmosphere, only film thickness reach more than 35 microns can reach the magnitude 9, the rest of the film thickness of the degree of corrosion is serious, the film thickness of 15 microns sample only level 7.Britain's test showed that Marine atmosphere is not the most severe test conditions, although the international standard for this American Florida test for the regulation of atmospheric corrosion area, is not actually can represent all of the atmospheric corrosion, strictly speaking, should choose to use the environment close to the test station to get the test data is more reliable.