The thermal conductivity of plasma electrolytic oxide coatings on aluminium and magnesium

Plasma electrolytic oxide coatings have been produced on both aluminium and magnesium substrates. Their microstructures have been studied and deductions made about formation conditions. The thermal conductivities of the coatings have been measured using a simple steady state method. The values obtained are relatively low (∼1 W m−1 K−1). This is explained in terms of the microstructure, which exhibits an extremely fine grain size and a significant proportion of amorphous phase. The porosity levels are low, so the low conductivity is not due to the presence of pores. It is noted that, even with a thickness limit of the order of 100 μm, coatings with such low conductivity may prove useful as thermal barrier layers, particularly since they exhibit excellent adhesion characteristics.