The Effects of Solar Radiation on the Surface Temperatures of Various Alloys Exposed to Atmospheric Corrosion Conditions

摘要

The surface temperature of alloys of different base metals will equilibrate to different temperatures depending on their solar reflectance index (SRI). The buildup of corrosion products can also have a significant effect on specimen surface temperatures due to changes in emissivity, which affects the SRI. In this study, the surface temperatures of exposed metallic specimens (i.e., UNS Z15001 zinc, UNS M11311 magnesium, UNS G10080 steel, UNS S30400 stainless steel, UNS C11000 copper, UNS A91060 aluminum, UNS A92024 aluminum and UNS A96061 aluminum) of varying exposure times were monitored in severe marine (Marine Corps Base Hawaii), rain forest (Lyon Arboretum), and high-altitude (Mauna Loa Observatory) environments. The emissivities of virgin and exposed specimens were measured. The maximum recorded temperature difference that occurred simultaneously for samples located at the same site (Lyon Arboretum) was 29.1°C between UNS C11000 copper and UNS A96061 aluminum. The smallest temperature variations occurred between virgin samples deployed at the Mauna Loa Observatory where solar radiation was high, but corrosion product formation and ambient air temperatures were low. The emissivites of the virgin samples were predictably low (typically e ≤ 0.1). The formation of corrosion products increased emissivities, but to different extents based on the alloy type. In some cases, differences in emissivities were measured for the sky-facing and ground-facing sample surfaces. A correlation between daytime peak temperature and accelerated evening cooling was also observed. That is, the hottest specimens during the day were also the coolest at night, resulting from large emissivity values.