Metallographic Examination of Fine Gold and a Gold-Copper Alloy for Coin Manufacturing

The mechanical properties and microstructures of alloys play an important role in the different steps of the coin manufacturing process. Only few data are available for the precious metals gold and silver as well as for their respective alloys. Several different circular coin blanks were metallographically examined in order to provide a better estimation of the impact of the production steps on the material. An electrochemical polishing method was developed aiming at obtaining contrast-rich and artifact-free micrographs. The microhardness was systematically measured on the whole surface of polished cross sections in order to generate distribution mappings. Object of the examination was fine gold (Au 999.9) and ducat gold (Au 986) which are primarily used to manufacture bullion and collector coins.