Abstract
To develop an improved surface treatment for producing metallic luster on magnesium alloys by controlling surface roughness, we analyzed the angle of incidence ψ, the instrument acceptance angle Δθ and the root mean square slope m, for experimental results on specular glossiness Gs and root mean square roughness σ. First, we derived a theoretical equation from the theory of electromagnetic waves and a model of surface roughness, assuming that the root mean square roughness is much smaller than the wavelength of the incident radiation. In this equation, the ratio R/R0 of the specular reflectance of the specimens to the specular reflectance of a smooth surface indicates the sum of the specular reflection component and the scattering reflection component for the instrument acceptance angle. This reflectance is a function of the angle of incidence. In this study, angles of incidence of 20°, 60° and 85° were used. Next, the specular glossiness and the root mean square roughness were measured for the surface of AZ31 magnesium alloy specimens treated with acidic aqueous solution. The value of the root mean square slope was obtained from the theoretical equation and was compared with the experimental results. We found that the experimental results matched the results calculated for an angle of incidence of 20°. These results clarified that the reflectance R/R0 is a function of σ/λ, the angle of incidence ψ, the instrument acceptance angle Δθ and the root mean square slope m. These results will be useful for developing better surface treatments for producing metallic luster on magnesium alloys.
