Abstract
Hydro-thermal technology had been used to improve the anti-corrosion and anti-wear performance of anodizing coating on the surface of aluminium alloys. The micromorphology of the coating has been studied by SEM and results proved the coating had a compact structure. The element in the substrate had been characterized by EDS and results proved Fe had redissolved to the Al substrate. The crystalline structure of the coating had been studied by XRD and results proved the anodic coating could be transformed into η-, p- and γ-alumina. The electrochemical properties had been researched using an electrochemical workstation; results proved after the coating had been treated by hydro-thermal technology, its anti-corrosion properties could be improved. At the hydro-thermal temperature of 400 ℃, its open circuit voltage and impedance reached −0.46 V and 160 kΩ × cm2, respectively. The hardness of the coating had to be measured with an HVS-100 micro-hardness tester, with results proving that, after the hydro-thermal treatment, the hardness of the coating increased to 150 HV. The friction coefficient of the coating had been studied using a ball-on-disk tester, and the results proved it decreased to 0.46. The MMW-2 scratch tester had been used to measure the adhesion between the coating and substrate; results proved the coating had better adhesion with the substrate. The thermal conductivity of the coating had been studied by a heat conduction coefficient measurement device; results proved that it reached 11.2 W/m × K at a hydro-thermal temperature of 400 ℃, far higher than that of organic coating.
Highlights
Aluminium alloys have high heat conductivity, high specific strength, and no lowtemperature brittleness
After the anodic coating was treated by hydro-thermal technology, the hardness of the coating increased
A compact crystalline alumina coating had been prepared on the surface of alloy 5052 (AA 5052), by combining anodizing and hydro-thermal technology
Summary
Aluminium alloys have high heat conductivity, high specific strength, and no lowtemperature brittleness. It is well known that crystalline alumina oxide has higher thermal conductivity, anticorrosion, and anti-wear performances than that of amorphous alumina [15,16,17]. If the amorphous alumina can be transformed into crystalline alumina, its anti-corrosion and anti-wear properties can be improved. When the amorphous alumina particle is treated by hydro-thermal technology, it can be transformed into crystalline alumina [20,21,22]. The relationship between hydro-thermal temperature and the crystallinity of alumina particles has been studied by many researchers [23,24,25]. If the anodic coating was treated by hydro-thermal technology at a suitable temperature, a compact crystalline alumina coating could be prepared. Based on the above analysis, using hydro-thermal technology can improve the anticorrosion or anti-wear of the anodic coating. The thermal conductivity of the coating was researched and compared with that of the anodic coating, proving the heat transfer performance of the coating could be improved
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