Copper and Alloys
The most important physical properties of copper are its high electrical conductivity, its high thermal conductivity and its excellent resistance to corrosion. There are three basic commercial grades of copper are available - tough pitch copper which is oxygen bearing, oxygen-free high conductivity copper and phosphorous deoxidised copper. The phosphorus deoxidised grade was originally developed to overcome problems when flame welding tough pitch copper, and is now the standard commercial weldable grade used for pressure vessels and radiators. The oxygen-free grades have significantly higher electrical conductivity than the oxygen bearing grades and are therefore used as electrical conductors. There is also a wide range of copper alloys including: · Brass - these alloys can contain up to 45% Zn, sometimes with additions of Sn, Pb, A1 Mn and Fe. Solid solution alloys contain up to 37% Zn and can be cold worked. The are used for pressings, shell cases, ornaments etc. Maximum ductility is obtained in the 70/30 brass, which is used for the deep drawing of cartridges. Lead is sometimes added to aid machining and tin for corrosion resistance in salt water. · Bronze - is a copper and tin alloy and is one of the oldest engineering materials known. They are used for coins, springs and ornaments, depending on the particular alloy. Admiralty gunmetal (88% Cu, 10% Sn, 2% Zn) is used for pumps and valves in the marine industry. · Cupronickel - as the name suggests these are copper rich, nickel containing alloys used mostly in marine environments. · Aluminium-bronze - these have between 5 and 10% Al in copper with small amounts of Fe, Mn and Ni. They have good strength and corrosion resistance and are widely used in heat exchangers. · Silicon bronzes - contain 1 to 5% Si as well as Mn, Fe and Zn. They are ductile, have excellent corrosion resistance and are readily welded.
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