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This paper presents the progress of an ongoing corrosion study of vehicle microenvironments. The study identifies the difference of corrosion microenvironments at various automotive proving grounds, using a sensor-equipped vehicle. A vehicle was instrumented for the proving ground test study. Various types of environmental sensors were installed at more than thirty-five sites on the vehicle. These sensors measured the temperature and relative humidity of the ambient air, and the temperature and time-of-wetness of the sites' surfaces. Cold rolled steel (CRS) and Zinc (Zn) corrosion rate sensors were also used in the experiments. The comparative analysis of vehicle microenvironments and corrosion rates of CRS and Zn, from three corrosion proving ground tests, will be discussed.

Galvanic corrosion of high purity die cast magnesium alloys AM50 and AZ91 was examined in accelerated atmospheric corrosion testing according to Volvo STD 1027,1375 for 6 weeks involving cycling of the relative humidity between 90% and 45% in combination with intermittent immersion in one of two NaCl-solutions (0.3% or 1.0%). The exposures were performed at two different CO2 levels; 0.01% and 0.3%. The initial general corrosion rate of the AM50 alloy is 50-100% higher than that of AZ91 depending on surface preparation. The corrosion weight loss of both materials depends linearly on salt load in the investigated range. CO2 has a moderate accelerating effect, being higher with decreased salt load. Extreme value analysis was used to evaluate the deepest pit distribution around the perimeter of mounted bolts in panels of AZ91 and AM50. Quite contrary to the general corrosion results, AZ91 showed 30% deeper pits than AM50.

Electrochemical Impedance Spectroscopy (EIS) and Thermal Wave Imaging (TWI) are complementary techniques which can be used to detect and estimate Impact Induced Corrosion (IIC) at the metal-polymer interface. This paper describes the use of the above techniques to detect Impact Induced Corrosion in a variety of pre-coated and painted sheet steels. It has been possible to show, that IIC is a threshold phenomenon and depends on the type of galvanized coating. Evaluation of IIC, using a high performance indoor accelerated test and preliminary data from the proving grounds are presented in this paper.

An extensive atmospheric corrosion test program to simulate automotive field conditions has been successfully completed. This paper focuses on the corrosion results from the widely exposed AISI set of correlation panels for cosmetic corrosion. Eight factorially designed 12-week tests have been performed in the laboratory, using high performance test equipment, capable of simulating diverse outdoor conditions. The results have been compared with those of outdoor scab exposures and reference panels on vehicles, running in Canada and Sweden. The influences of six corrosive test variables on the response creep-back from scribe on the painted panels are demonstrated, based on a statistic evaluation of the test matrix. All higher settings of the introduced accelerating test variables have each resulted in a decrease in the test correlation with on-vehicle exposures.

An extensive atmospheric corrosion test program to simulate automotive field conditions has been undertaken. The aim of this project is to identify the necessary and sufficient key corrosion variables in appropriate dosage levels in order to design an indoor general purpose accelerated corrosion test. This approach is based on a careful study of outdoor conditions that an automobile typically would encounter along with inputs from current understanding in the area of corrosion and material properties. A 26-3 factorial design was used to implement this test program. Simulating conditions such as humidity, temperature cycling, acid and/or salt depositions, generation of dew and the presence of minute amounts of air pollutants have been achieved by the design and implementation of a high performance climate chamber. A large matrix of painted metal substrates and some bare metal samples along with previously studied AISI samples constitute this study.

An accelerated multifactor laboratory corrosion test with high correlation with respect to outdoor Volvo scab and field exposure is under way. It uses a mixture of SO2 and NO2 in ppm amounts at high humidity, combined with periodic soaking of the samples in acidified, diluted sodium chloride solution. A broad representation of precoated steel materials with cathodic electro-deposition primer and the full car body paint system was used to correlate the results to outdoor field and scab exposure. The results show that the conventional electrogalvanized and hot-dip galvanized zinc-coatings seem, from point of view of cosmetic corrosion, to be as good a choice as new generation precoating. The tested hot-dipped zinc-iron alloy coating performed very well, and was much more insensitive to galvanic corrosion than the zinc-coatings.