Metallographic preparation of copper and copper alloys Copper, together with gold and tin were the first metals put to use by ancient man. The ease with which it could be shaped and formed, its attractive colour and its corrosion resistance were among some of the reasons why it found widespread use in the manufacture of early weaponry, jewellery, liturgical vessels and everyday domestic objects. Application Notes Metallic copper has been known since about 9.000 BC and was widely used by 5.000 BC. When its value as an alloy with tin was recognised, the birth of the Bronze Age initiated a profound cultural and economic development in Europe and the Mediterranean countries. Historically, casting of bronze has a long tradition, but it is only since the 1920s that hot rolling and extrusion of copper and its alloys have been practiced. Nowadays, most of the copper produced is in wrought form, and with its high electrical conductivity copper is much used as cables, switchgear components, transformers, motor windings, and generators. Oxygen free copper is mainly used in the electro-nics industry. The corrosion resistance and high thermal conductivity of copper make it suitable for tubes, vessels and heat exchangers in the chemical, and food and beverage industry. Apart from the traditional applications of Aluminium bronze, CuAl8, shows dendritic structure with α-δ eutectoid. Colour etching according to Klemm, pol. light, 100x. copper for water and heating pipes, architects have in recent years discovered the appeal of designing facades with oxidised copper sheets. The metallography of copper and its alloys is used for grain size measurement and purity checks by qualifying and quantifying the copper oxide content. On occasion, in certain brasses, the distribution of lead is determined as it can influence the machining process. In cast alloys the general microstructure and distribution of eutectic or lead is evaluated as well as the presence of shrinkage cavities or porosity. Difficulties in the preparation of copper and its alloys Pure copper is soft and ductile, easy to deform and prone to form scratches. Bronzes, and even some of the harder brasses, may be susceptible to severe scratching. Solution - Avoiding coarse grinding abrasives - Thorough diamond polishing with soft cloths - Chemical-mechanical fine polishing Fig.1: Pure copper wire, with final polish of OP-S, DIC, 200x. Fig. 2: Same sample as Fig.1 with final polish of OP-S-ammonia water-hydrogen peroxide-mixture, DIC, 200x.
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