Compositional tuning-induced permanent color adjustment and mechanical properties: Binary Cu-Mg colored metallic system

Abstract

Cu-Mg binary alloys consist of a relatively simple mixture of eutectic reactions (L ➔ f.c.c. Cu + MgCu2). Since they have different color, i.e., the copper with L* = 86, a* = 14, b* = 16 and the MgCu2 with L* = 91, a* = 3, b* = 11, it can be suggested that the compositional tailoring can control the overall color of the alloys. In order to investigate the influences of the Mg contents on microstructure, color, and mechanical properties, series of the Cu-Mg colored near-eutectic and eutectic alloys were investigated for identifying color materialization and their properties, as well as the possibility of permanent color materialization in the metallic materials, was also investigated. With increase of Mg contents, the microstructure was transformed from a typical near-eutectic structure to MgCu2 polycrystalline structure, indicating the increased volume fraction of MgCu2 Laves-phase together with the enhanced hardness. In addition, the color variations expressed by means of L*a*b* color space migrated to the reduced a* and b* direction, suggesting the visual color of alloys changing from reddish orange color to pale yellow color. Therefore, these findings indicated that the combination of two different colored phases can lead to the permanent color variations in metallic materials without any additional processes.