Anodizing is widely used as a surface treatment for aluminum alloy to improve its surface properties by increasing the thickness of the oxide layer. Generally, conventional anodizing by direct current (DC) produced high porosity and micro‐cracks. Utilizing pulse current (PC) as a power source and graphite particles as reinforcement for the oxide layer may solve these problems. Therefore, the present work aims to study the effect of the combination approaches on coating growth and the surface characteristics of the oxide coating. The graphite‐incorporated composite oxide coating on the AA2017‐T4 Al alloy was developed by DC and PC hard anodizing process. The surface morphology, topography, chemical composition, and surface hardness were evaluated. In PC anodizing, the growth rate of oxide layer was slower (0.59 μm/min) than DC anodizing (1.08 μm/min). The surface pores start to develop at the 30th minute compared to DC, which is the 20th minute. At 60 min, the formation of porous composite oxide coating is complete with pore dimension (width: 46.74 ± 19.96 μm and depth: 7.11 ± 2.57 μm) and thickness of 35.20 ± 8.90 μm for PC, whereas for DC pore dimension (width: 81.03 ± 21.60 μm and depth: 17.16 ± 4.31 μm) and thickness of 64.80 ± 23.69 μm. Surface roughness and hardness of composite oxide coating by PC were measured at about 1.90 ± 0.04 μm and 379.10 ± 4.37 HV, respectively. Meanwhile, the DC reveals a significant increase in roughness (4.28 ± 0.25 μm) and a decrease in hardness (302.75 ± 1.09 HV). The introduction of graphite particles with PC anodizing reduces the surface porosity, microcracks and enhances the surface hardness of oxide coating.
Anodic Alumina Oxide (AAO) is one of the nanomaterials that have developed as a template in the nanowires, nanodots and nanotubes. This research focuses on synthesizing AAO by two different electrolytic solutions which are using sulfuric acid (H2SO4) and oxalic acid (C2H2O4) by electrochemical anodization method. Two parameters were influencing the anodization process in the experiment; the type and the concentration of the electrolytic solution. The effects of the different type of electrolytic solutions produced different size of pores. When the voltage used is 25 V in H2SO4, the optimum reading size of the nanopores is in the range of 16-22 nm, whereas the AAO pores in C2H2O4 are in the range of 100-200 nm. Meanwhile, the concentration of H2SO4 and C2H2O4 is set to be 0.3 M, 0.4 M and 0.5 M., The results in 0.3 M H2SO4 and C2H2O4, show the optimum concentration of electrolytic solutions which is the key parameter affecting the morphological structure of porous membranes in AAO. The optimum value for these two acidic solutions has produced such highly ordered arrangement of nanopores which are from the average size of nanopores that anodized in sulfuric acid is 19 nm while 120 nm in oxalic acid. The morphological structure properties of AAO templates include the diameter of nanopores, the thickness of membrane and density of nanopores would be examined by Field Emission Scanning Electron Microscope (FESEM) and Energy Dispersive X-ray (EDX). Also, Fourier-transmittance infrared spectroscopy (FTIR) detected the chemical functional group of bonds in AAO. In conclusion, AAO templates have a big potential to be the major contributor in the future for the development of new electronic devices.
This paper clarifies the surface difference and tribological performance of anodic oxide coating reinforced with three different carbon-based sources. With the rising age of oxide coating as one of the strongest metal surface protectors, modification and improvement of this coating have been rapidly explored, including reinforcing carbon-based materials. The lack of literature on how the correlation between the particles' size improves the surface condition and its tribological properties opens up the gap in expanding this coating's potential. In this study, aluminium alloy AA2017 has been chosen as the substrate to be anodized with three different carbon sources: micro-sized graphite, nano-sized graphite, and graphite plate. With a constant 2A current on the DC power supply, the substrate was anodized for 60 minutes in a 20% sulphuric acid electrolyte. The finding shows that the anodic oxide with nano-sized graphite produces the highest hardness surface with almost 50% improvement compared to the unreinforced anodic oxide coating with no visible micro-cracks on the surface observed. Tribologically, the anodic oxide reinforced with micro-sized graphite produced the lowest coefficient of friction and wear rate at 0.4 and 1.25x10-5 mm3/Nm, respectively. The wear track image shows traces of debris that are different for each type of anodic coating that might be influenced by the surface roughness and hardness of the coating.
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