Alloys zinc-based

Zinc consumption is categorized in five semifabricating markets (see Table 15). Galvanizing was the main market for zinc in the 1970s followed by zinc-base casting alloys and brass and bronze. Depressed constmction and automotive industries caused a decline from 1979 to 1980 of ca 18%, and the die-casting business declined 34% and galvanizing 24%. 

Because zinc-based alloys have low melting points, energy savings in the melting operation are substantial and the foundry operation is essentially free of fume. With the current trend of increasing energy costs and pollution control, cost benefits can be considerable (114). 

Forming-Die Alloys. The tonnage of slab zinc used in this appHcation is small. The use of zinc alloy dies started in the aircraft industry during World War II (119). Zinc-based alloys cast in sand and plaster molds continue to be used for short-mn dies for steel and aluminum stampings in the automotive and aircraft industries (120). Considerable cost savings are realized with these low melting zinc-based alloys which are easy to poHsh, machine, weld, and remelt. 

Kretzschmar, E., Metaii, Kermik and Piasispritzen, V. E. B. Verlag Technik, Berlin (1970) Leclercq, M. and Bensimmon, R., New Zinc-based Alloy for Metallising . Proc. 8th Int. Thermal Spray. Conf., American Welding Society, pp. 417-429 (1976)... 

As a decorative finish on steel and zinc-base alloys for a variety of domestic and ornamental articles. The finish may be protected by clear lacquers or may be coloured by metal colouring techniques for use on, for example, door handles, luggage trim, etc. 

Chemical deposition Simple immersion deposits of copper may be obtained on iron and steel in a solution containing, for example, 15 g/1 of copper sulphate and 8 g/1 sulphuric acid, and on zinc-base alloy in a solution containing copper sulphate 300 g/1, tartaric acid 50 g/1 and ammonium hydroxide 30ml/l . Such deposits are thin and porous and are mainly plated for their colour, e.g. for identification, or for their lubricating properties, e.g. in wire drawing. 

Corrosion resistance The corrosion resistance of a copper deposit varies with the conditions under which it is deposited and may be influenced by co-deposited addition agents (see, for example, Raub ). Copper is, however, plated as a protective coating only in specialised applications, and the chief interest lies in its behaviour as an undercoating for nickel-chromium on steel and on zinc-base alloy. Its value for this purpose has long been a controversial issue. 

A further development is the use of a combined chromium-nickel-chromium or nickel-chromium-nickel-chromium deposit on steel- or zinc-base alloy articlesAn advantage of this system is that the first chromium layer need not be plated within the bright range of the chromium bath, so that plating can be carried out under conditions giving deposits of maximum corrosion resistance such conditions do not coincide with those under which fully bright chromium plate is obtained. 

In view of the high cost, when tarnish resistance of the surface is the only requirement it is customary to use the thinnest possible coatings of rhodium (0-000 25-0-000 5 mm). Since rhodium deposits in this thickness range, like thin electrodeposits of other metals, show significant porosity, readily corrodible metals, e.g. steel, zinc-base alloys, etc. must be provided with an undercoating deposit, usually of silver or nickel, which is sufficiently thick to provide a fairly high level of protection to the basis metal even before the final precious metal deposit is applied, and, in this way, to prevent accelerated electrochemical corrosion at pores in the rhodium deposit. 

Park and Szpunar [318] have shown that the texture, surface morphology, alloy composition, and phase composition of zinc-based coatings strongly influence corrosion resistance. 

The zinc-base dic-casting alloys are the mast widely used. A typical composition is 1.0% copper. 3.9% aluminum, 0.06% magnesium, balance zinc. This alloy has a strength of about 43.000 psi (3.061 atmospheres) with 3% elongaliun in 2 inches (3 centimeters). Typical applications are carburetors, fuel pumps, tools, typewriter frames, instrument cases, and hardware often finished by chromium plating. 

Care has to be taken in selecting materials for the die and punches. Metals are of little use above 1000 °C because they become ductile, and the die bulges under pressure so that the compact can only be extracted by destroying the die. However, zinc sulphide (an infrared-transparent material) has been hot pressed at 700 °C in stainless steel moulds. Special alloys, mostly based on molybdenum, can be used up to 1000 °C at pressures of about 80 MPa (5 ton in-2). Alumina, silicon carbide and silicon nitride can be used up to about 1400 °C at similar pressures and are widely applied in the production of transparent electro-optical ceramics based on lead lanthanum zirconate as discussed in Section 8.2.1. 

Zinc-Base Alloys. I. General Introduction. The Application of the Linear Sweep Cathode Ray Polarograph. Anal. Chim. Acta 18, 345 (1958). 

INSTRUMENTAL PARAMETERS FOR THE ANALYSIS OF ZINC-BASED ALLOYS... 

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