Investigation of diamond turning: of rapidly solidified aluminum alloys

Abstract

Aluminum 6061 is often considered the preferred material for manufacturing optical components for ground-based astronomical applications. One reason for using this material is its high specific stiffness and excellent thermal properties. Moreover, a large amount of data exists for this material and commercially available aluminum 6061 can be diamond turned to achieve surface roughness values of approximately 4 to 8 nm, which is adequate for applications that involve the infrared spectral range, but not for the near-ultraviolet wavelength (NUV) spectral range. In this study, we used a novel aluminum material, fabricated using a rapid solidification process that is equivalent to the conventional aluminum 6061 alloy grade. Using rapidly solidified aluminum (RSA) can achieve improved surface finish and enhanced optical performance. The rapid solidification process was realized using a melt spinning operation, which achieves a high cooling rate to yield a fine microstructure. The properties of RSA 6061 are similar to those of conventional aluminum 6061, but its grain size is extremely small. In this paper, the background of RSA is introduced, and the diamond turnability characteristics and coating processes for both traditional aluminum 6061 and RSA are discussed. The surface roughness and grain structure of RSA were evaluated using white light interferometers and the surface roughness during coating of the reflectance multilayers of samples were analyzed using near-ultraviolet wavelengths. Finally, indicators such as optimal cutting parameters and optical performance are discussed.