Zinc and Its Alloys

The chief ores of zinc are zinc blende ( Zinc sulphide ) and calamine ( Zinc carbonate ). In the extraction of the metal, the ore is first roasted in a reverberatory furnace to convert the sulphide to oxide, and in the case of calamine, to drive off carbonic acid and water. The roasted ore is then reduced either in a furnace or electrolytically.

Zinc is a fairly heavy , bluish - white metal used principally because of its low cost, corrosion resistance, and alloying properties. The melting point of zinc is 419 *C.

The protection of Iron and steel from corrosion is done more often with zinc than with any other metal coating. The oldest and most important methods of applying the zinc coating are known as galvanizing. When rolled into sheets, zinc is used for roof covering and for providing a damp-proof non corrosive lining to containers , etc. Zinc casts well and forms the base of various die-casting alloys.

A typical high strength die - casting alloy would have ,

Cu = 1.25 % , Fe = 0.1% , Sn = 0.007 % , Al = 4 % , Pb = 0.007 % , Mg = 0.08 % , Cd = 0.007 %

Zn = remaining %

Properties of die casting alloys are ,

UTS = 32 kg-f /mm2 or 320 M pa percent elongation = 7 %

Charpy Impact No. = 65 J or 6.5kgm \

Melting Point = 425 *C

Comments

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