Constructing Colorful Surfaces with Mechanical Robustness for Magnesium Alloys via a Reagent-Free Method

The colorful and mechanically robust surfaces of metallic materials are important for their applications in electronics, automobile, aerospace, and so on, but it is challenging to prepare them at a reasonable cost. Herein, we propose a simple, environment-friendly, and cost-effective method, reagent-free hydrothermal treatment, to prepare colorful surfaces of magnesium alloys with mechanical robustness. The as-treated surface mainly composes of magnesium (hydr)oxides with a biomimetic microstructure, whose thickness and roughness increase linearly with the hydrothermal time. By adjusting the hydrothermal time, a series of surface colors of magnesium alloys are obtained because of light interference. The as-treated surface with film thickness more than 1.1 μm exhibits high Vickers hardness (∼500 HV), low friction coefficient (∼0.26), and low wear rate (1.06 × 10^-5 mm³·N^-1·m^-1), which is superior to most magnesium alloys after surface treatments. The microstructure of the as-treated surface can be retained after harsh tribological tests, demonstrating attractive mechanical robustness. Furthermore, the method proposed here was extended to the surface treatments of other series of magnesium alloys, which verifies the great potential of this method for large-scale industrial application of colorful metallic materials with mechanical robustness.