Formation of a composite anodic oxidation film containing Al 2 O 3 particles on the AZ31 magnesium alloy

Abstract

A composite film containing Al 2 O 3 nanoparticles was successfully anodized on the AZ31 alloy using an alkaline NaOH-Na 2 SiO 3 solution. The formation process and the mechanism of the nanoparticles were investigated by means of XRD, SEM and EDS characterization. The addition of nanoparticles does not change the basic process of anodizing magnesium alloys. The thickness change of the oxide films is consistent with the voltage variation and the oxidation time. During the first 5 seconds of anodization, the sample weight decreases, indicating that Mg dissolution dominates this process. Subsequently, the sample weight begins to increase and the film development plays an important role. The oxide film is formed by Al 2 O 3 nanoparticles absorbed on the surface of the magnesium matrix. The nanoparticles have been involved in the growth process of the oxide films. The composite oxide film is composed of MgO, Mg 2 SiO 4 and -Al 2 O 3 phases. In the process of composite oxidation, Al 2 O 3 nanoparticles can fill in the pores and the cracks of the oxide films after being absorbed on the surface of the film. In addition, they can also be continuously captured in the oxide film, forming an oxide film structure reinforced by Al 2 O 3 nanoparticles and leading to enhanced performance.