Studies On Preparation Of Oxidation Surfaces On Aluminum Substrate And The Insulation And Thermal Conductivity Of The Surfaces

Thermal conductivity of insulation layer on traditional LED aluminium substrate is poor.Aimed at this problem,oxide films on the surface of aluminum substrates was prepared by micro-arc oxidation with different pulse widths and anodic oxidation with different electrolyte systems to replace the epoxy resin insulation layer in traditional aluminum substrates.By means of XRD and SEM,the micro-morphology,phase and corrosion resistance of the films were tested and analyzed,and the effects of oxidation process on the thermal conductivity of the films were systematically studied,which provided reference and data support for the application of micro-arc oxidation and anodic oxidation processes in the field of aluminum substrates.The results show that:With the increase of pulse width,the thickness of the micro-arc oxidation film on the surface of aluminum substrates first increases and then decreases,and the number and size of the micro-holes on the surface increase gradually,the ratio of the main components in the oxide film,a-Al2O3 and y-Al2O3,increases gradually.With the increase of pulse width,the volume resistivity of micro-arc oxidation film on the surface of aluminum substrate increases gradually,the breakdown voltage increases first and then decreases,and the thermal conductivity increases slightly.When the pulse frequency is 500 Hz,pulse width is 800 microsecond,the film has the best comprehensive insulation performance.volume resistivity is 8.6×1014?·cm,breakdown voltage is 1240V,which meets the requirements of insulation performance of aluminum substrates.Meanwhile,thermal conductivity is 27.09W/m-k,which is two orders of magnitude higher than that of epoxy resin.The thickness of anodic oxide film on aluminium substrate prepared by sulfuric acid,oxalic acid and mixed organic acid electrolyte system increases first and then decreases with the increase of electrolyte concentration.When sulfuric acid concentration is 140g/L,oxalic acid concentration is 60g/L,mixed organic acid includes 100g/L sulfosalicylic acid and 40g/L malic acid,the prepared anodic oxide film has the best insulation performance:volume resistivity of sulfuric acid oxide film is 6.2×1011?·cm,breakdown voltage is 1420V;volume resistivity of oxalic acid oxide film is 3.6×1012?·cm,breakdown voltage is 1200V;volume resistivity of mixed organic acid oxide film is 7.1×1013?·cm,breakdown voltage is 1510V.it all satisfies the requirement of insulation performance of aluminium substrates.The thermal conductivities of the three anodic oxide coatings are 15.84W/m K,17.53W/m K and 20.70W/m K,respectively,which show good thermal conductivity compared with epoxy resin.The results of electrochemical impedance spectroscopy show that the corrosion resistance of micro-arc oxidation and mixed organic acid anodic oxidation film is excellent,which can shield the ion erosion in electrolyte and ensure that the copper foil circuit is not corroded in the later etching stage of aluminum substrate.