In a previous paper we reported about the use of rapidly solidified aluminium (RSA) for optical applications [1]. RSA has a small sized grain structure enabling it to be diamond turned to low surface roughness values. This paper describes the diamond turning investigation for both RSA-6061 and RSA-905. We show that RSA-905 can be diamond turned to a surface roughness value of 2 nm Rq, (Higher Extrusion Ratio to about 1,5nm), while the RSA-6061 can be diamond turned to 1 nm Rq, provided that the proper post processing of the material after melt spinning is given. It is shown that the surface roughness values are influenced by mainly the amount and size of Mg2Si precipitates that are present in the base material. Using an optimized processing to get the Mg2Si precipitates better into solid solution enabled us to achieve 1 nm Rq surface roughness for the heat treatable RSA-6061, see Figure 1. We show, using a bidirectional reflectance distribution function measurement, that the RSA-6061 does not have to be post-polished.
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