Development of accelerated corrosion tests involving alternative exposure to hostile gases, neutral salt spray and drying

Abstract: In this thesis, a well proven corrosion testing method developed by SP Technical Research Institute of Sweden (SP) ISO 21207 method B is modified in order to increase even further the acceleration factor of corrosion attacks by 40%. The method combines humidity cycling with conditioning, drying as well exposure to corrosive substances SO2, NO2 and NaCl solution.ISO 21207 method B is modified into three modifications; Modification A, Modification B and Modification C. In Modification A the quantity of gas is increased by 50% for SO2 and 25 % for NO2 during gas exposure. For Modification B the pH of the NaCl solution is decreased to 3-4, during salt spray test. The last Modification C is a combination between Modification A and B i.e. a higher quantity of gas and a lower pH. Coupons of aluminum, AluZn, carbon steel, copper and zinc are exposed, both at SP and at SAAB. The geometrical size of the coupons is 25 cm2 and the coupons are prepared by grinding and polishing down to 9 µm diamond, washing with ethanol in ultrasonic bath, drying in warm air and weighed before test. The coupons are then exposed to salt and hostile gases according to ISO 21207 method B, Modification A, B and C. The corrosion products are then removed by chemical cleaning in ultrasonic bath and the total mass loss is calculated. In this thesis copper is the most interesting metal since the method is mainly used for electronic components where copper is the dominating metal. In the case of copper all tests accelerate the corrosion rate but Modification C accelerates the most. However, the corroded surface in Modification C is very different compared to that of the coupons exposed to the standardized method ISO 21207 method B. Surface analysis shows that the corrosion products are changed when exposing to Modification C.