Test accelere de corrosion alternatif au brouillard salin selon la norme ASTM B117

An accelerated corrosion test is generally defined as a method that assesses the performance of metals and coatings and the results are obtained after a period of time shorter than with natural exposure.;The accelerated corrosion tests are essential for new materials, coatings and surface treatments development and qualification. However, for a variety of materials and coatings used in the aviation industry, these tests are unreliable and fail to reproduce the performance of corrosion resistance obtained in tests of long-term outdoor exposure or even under in service conditions. This lack of precision led to a heavy reliance on long-term exposure tests.;The salt spray test, such as defined by ASTM B117, is one of the most widely used proof tests for evaluating corrosion protection provided by organic and inorganic coatings on metals, including aluminum alloys, and is frequently quoted in specifications as a quality control tool. This method can take several hundred hours, in addition to being the subject of many controversies in the literature.;Despite its known limitations such as time, costs and subjectivity, the salt spray test is considered a reference in the aerospace industry. Explaining why, Bombardier Aerospace, a leader in the aircraft construction field and host company for this master degree, proposed to conduct an experimental research project in collaboration with the "Ecole Polytechnique de Montreal". The scope of this project is to develop test able to assess the ability of different anodized aluminum alloys to resist corrosion attack by overstepping salt spray test limits. For Bombardier Aerospace, the intent is not to replace the salt spray test but rather to develop an alternative method that will predict salt spray pass or failure.;The alternative method must be simple, objective and fast. It should be able to assess finished aluminum alloys, with chromic acid anodizing, quality. Coating specifications and test coupons are provided by the company.;To meet Bombardier Aerospace requirements, the "Cathodic Breakdown Test" CBT among all electrochemical methods was chosen. The CBT appears to be the most promising test and the most likely to correlate with salt spray test. Moreover, CBT is a specially designed electrochemical method for evaluating anodized coatings on aluminum and aluminum alloys.;The CBT has been used in the aeronautical industry for about 15 years (from 1978 to 1993), at least, on an informal basis to evaluate process shifts of chromic acid anodized aluminum coatings [1]. The collected CBT data appeared promising enough to evaluate the correlation between this test results and the salt spray data on a pass/fail basis. An experimental method was put in place to evaluate the corrosion resistance performance of a typical chromic acid anodizing process. At the end, 63 tests were conducted and correlation parameters and criteria were established. Their use allowed an accurate prediction of salt spray failure: samples that failed CBT, also failed in salt spray. The author concluded that the CBT results correlate well with those of the salt spray.;The CBT, not being a standardized test and lacking approved methodology in the literature, this work is devoted to develop a complete experimental procedure for cathodic breakdown testing, to study the correlation between CBT and salt spray testing results, to discuss the accuracy of the correlation parameters presented in the literature, and finally, to evaluate the CBT as useful quality control tool in the aerospace industry. This study will be based on aerospace industrial materials, and will focus on chromic acid anodizing coatings with a large range of sealing performances.;Ultimately, a new testing method of corrosion performance, overcoming salt spray limitations, will be presented (10 minutes for CBT versus 336 hours for salt spray).;Data examination showed that the CBTcombined parameter increases with the salt spray test time to fail, and that the CBT is very responsive to the sealing quality. Thus, the CBT is identified as a tool with the ability to predict failures in salt spray cabinet and could be use for this aim at Bombardier Aerospace's locations. The CBT integration as an alternate test to salt spray would allow a considerable reduction of salt spray testing, deliver great time savings and provide objective quantitative data. However, re-evaluating correlation criteria and parameters is necessary to qualify the CBT as a standalone quality control tool.