Accelerated Prediction Methodologies to Predict the Outdoor Exposure Lifespan of Galvannealed Steel

Abstract

Parameters to affect atmospheric corrosion can be divided into chemical and physical factors [1-9]. Chemical factors include oxygen, ozone, moisture, sulfur dioxide, salt, dust, acid rain, inclusion on the surface, and other gases. Physical factors are mainly temperature, wind intensity, and sunlight. These factors may be changeable with seasons and the natural environment, and these climate changes influence the corrosion behavior of metals and alloys. In general, the environments in which the metals and alloys are applied can be classified into coastal, industrial, urban, and rural areas [9-13]. However, it should be noted that the above classification is greatly simplified. The applied environment can have a large effect on the lifespan of every metal and alloy, and thus the estimation of lifespan needs to fully understand and take into account the environment [14]. When metallic materials are used or exposed outdoors, degradation can take place by the natural environment, such as sunlight, humidity, rain, dew condensation, and pollutant gases in the air, and thus weather resistance, corrosion resistance, and durability are lowered. Therefore, in order to measure the properties in the air, the optimum method is the atmospheric outdoor exposure test [15-18]. The atmospheric outdoor exposure test evaluates the effect of the environmental factors (Cl, CO, NOx, SOx, O3) including weather factors (temperature, humidity, quantity of solar radiation, snow, and rain) on the degradation of industrial products (automobile, train, tire, bridge, road facilities, metals, textile, rubber, antenna, cables etc.) that are used or installed at outdoor sites. Because the outdoor exposure test is one of the essential reliability evaluation methods to improve the quality, and estimate the lifespan of new materials or products, it is considered to be very important. Recently, our group reported the atmospheric corrosion of galvanized steels in Korea [19,20]; when the exposure time was increased, the content of Zn from galvannealed steel GA surface decreased while the contents of iron and oxygen tended to increase [19]. With increasing exposure times, the galvannealed steel GA specimen became blackened by the formation of zinc oxide, and red coloration was increased by the formation of red rust. As the exposure time of galvanized steel GI specimen increased, the surface proceeded to blacken, but no red rust was formed and the color did not change significantly. Accelerated Prediction Methodologies to Predict the Outdoor Exposure Lifespan of Galvannealed Steel