GROWTH MECHANISM OF DIAMOND-LIKE CARBON FLAKES REINFORCED OXIDE COATING ON AA2017 ALUMINIUM ALLOY

Abstract

The incorporation of diamond-like carbon (DLC) flakes in the oxide coating significantly reduced the surface defect and enhanced the microhardness of the composite oxide coating. However, the growth mechanism for type III disordered porous oxide coating and the crack reduction mechanism when incorporating DLC flakes in the oxide coating remains unclear. The study aims to clarify the growth mechanism by examining the oxide coating with and without incorporating DLC flakes at different anodizing times. Anodizing of the aluminium substrate (AA2017-T4) in 20 wt.% sulphuric acid (H₂SO₄) with a constant current of 2 A and 15 V initial applied voltage at the anodizing time of 2, 4, 6, 8, 10, 20, 30, and 60 minutes was performed. The result revealed that the disordered pores formed at 20 minutes of anodizing time due to fluctuating voltage when anodizing time increased. An initial increase in surface roughness was observed, reaching up to 7 µm at 8 minutes, followed by a sharp decrease to 1.8 µm at 10 minutes. Subsequently, the surface roughness increased again between 20 and 60 minutes of anodizing, ranging from 2.5 µm to 6.5 µm. The incorporation of DLC flakes in the oxide coating significantly reduced the formation of cracks and prevented them from propagating by occupying the pores. In addition, the DLC flakes also act as a physical barrier that hinders the dissolution of Al³⁺ into the electrolyte, which can cause further weakness in the oxide coating if the size of the pores increases. This study managed to reduce the knowledge gaps for the crack reduction mechanism of disordered porous oxide coating.