Microarc oxidation coated magnesium alloy radiator for light emitting diode: Microstructure, thermal radiative and dissipating property

Light emitting diode (LED) as a new generation light source whose lifetime and luminescence efficiency drop rapidly with the P-N junction temperature (T_j) increase. In this paper, a high emissivity ceramic coating fabricated by microarc oxidation (MAO) on magnesium alloy radiator enhanced the heat dissipation of LED. And the effects of MAO coatings with different phase composition on infrared emissivity and T_j were studied. The results show that Mg-Si-O and Ca-Mg-Si-O coatings exhibit a high emissivity up to 0.8 at 623 K within 8-20 μm wavelength range. The formation of CaSiO₃ phase in Ca-Mg-Si-O coating contributes to the short wavelength shift of the high emissivity region due to the enhanced lattice vibration absorption. The increasing coating surface roughness is beneficial to promote the emissivity. The enhanced thermal radiation with coated magnesium radiator significantly promoted the heat dissipating of LED. Compared with the uncoated magnesium radiator, the Mg-Si-O and Ca-Mg-Si-O coated samples with oxidation time of 10 min enable the temperature of LED to drop approximately at 6.2 °C and 7.3 °C, respectively.