Achieving atomic-level surfaces for aluminum alloys induced by a novel chemical mechanical polishing strategy using a developed polisher with yttria hybrid nano-abrasives

Abstract

Aluminum (Al) alloy has soft and plastic nature, easy to occur pitting, scratching, corrosion and wear. Chemical mechanical polishing (CMP) on Al alloys usually leads to a surface roughness (S_a) of more than 0.5 nm, making it a challenge to achieve atomic-level surfaces. To overcome this challenge, a novel, green CMP strategy was developed using a custom-made polisher, and the CMP slurry contained silica and yttria hybrid nano-abrasives, hydrogen peroxide, sodium tartrate and sodium phytate. After finishing of CMP, surface roughness S_a is 0.161 nm garnered on a 6061 Al alloy with a measurement area of 50 × 50 µm², and material removal rate is 41.25 nm min⁻¹. To the best of our knowledge, this Al alloy has the lowest S_a compared with those reported to date. Molecular dynamics simulations predicted that when the cutting depth was 15 Å in a three-body nano-abrasive wear, the surface roughness (S_a) was 0.169 nm. This was in good agreement with 0.161 nm measured using a three-dimensional surface profilometer. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy revealed that hydrogen peroxide oxidized the surface of the Al alloy, forming alumina and aluminum hydroxide. They were dissolved by hydroxyl ions released by the hydrolysis of sodium tartrate and sodium phytate. The dissolved ions were complexed by salts of tartrate and phytate, generating complexes. These oxidized layer and adsorbed complexes were removed by silica and yttria hybrid nano-abrasives, resulting in an atomic-level surface. Our outcomes provide a new route to achieve atomic-level surface for Al alloys via a novel, eco-friendly CMP strategy using yttria hybrid nano-abrasives.