Thermal studies on electrodeposited black oxide coating on magnesium alloys

Thermal behavior of black anodic coatings on magnesium alloy, AZ31B and mag nesium lithium alloy, MLA 9 has been investigated. The chemical nature of c oating is characterized by infrared spectral studies. The thermoanalytical investigations have been carried out using thermogravimetry (TG), derivativ e 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 temper ature was investigated using calorimetric methods. The studies revealed tha t the thermal emittance of coatings increases with temperature. Cc) 2001 El sevier Science B.V. All rights reserved.