Emissivity characteristics of roughened aluminum alloy surfaces and assessment of multispectral radiation thermometry (MRT) emissivity models

Experiments were performed to examine the emissivity characteristics of aluminum alloy samples over the spectral range of 2.05 to 4.72 μm and temperatures of 600, 700 and 800 K. AL 1100, 7150, 7075 and 2024 samples were tested which possessed polished, 6- and 14-μm surface finishes. Additionally, extruded and saw-cut samples were tested to examine the effects of extreme roughness on emissivity. For the polished, 6- and 14-μm samples, the emissivity decreased appreciably between 2.05 and 3.5 μm, and increased slightly between 3.5 and 4.72 μm. Spectral variations were far less pronounced for the extruded and saw-cut surfaces. Eighteen MRT emissivity models were examined for accuracy in temperature measurement. Drastic changes in the emissivity distribution precluded the use of a single function to accurately represent every band of the measured spectrum. Overall, two relatively simple models provided the best overall predictions for different alloys and temperatures. These are the same models that yielded the best overall results for polished aluminum surfaces in a previous study by the authors. Despite the relative success of these models, this study points to a need to greatly enhance the measurement accuracy of radiation thermometers to meet the needs of the aluminum industry.