Thermal studies on electrodeposited black oxide coating on magnesium alloys

Thermal behavior of black anodic coatings on magnesium alloy, AZ31B and magnesium lithium alloy, MLA 9 has been investigated. The chemical nature of coating is characterized by infrared spectral studies. The thermoanalytical investigations have been carried out using thermogravimetry (TG), derivative thermogravimetry (DTG), and differential scanning calorimetry (DSC). The decomposition proceeds through three steps viz., dehydration, decomposition of chromium hydroxide and sulphate and decomposition of magnesium chromate to oxide. Measurement of hemispherical emittance of coatings verses temperature was investigated using calorimetric methods. The studies revealed that the thermal emittance of coatings increases with temperature.