GB769483A - Zinc aluminium alloy and process for the production thereof - Google Patents

Abstract

A zinc-aluminium alloy, particularly suitable for workpieces having high strength to weight and for carrying out reciprocating movements or exposed to sliding or roling friction, has a composition within the following range .Zn.at least 20.per cent .Al.at least 20.per cent .Si.0.1 - 15.per cent .Cu.0.05 - 6.per cent The alloy may also contain one or more of the following elements up to 6 per cent in total namely Cr, Ti, Ca, Sr, Ba, Cd, Mn, Sn, B, C, V, Mo, Sb, W, Ce, P, Na and K with Fe or Pb as impurities only less than 0.1 in either case. The alloy may contain in addition Mg up to 6 per cent and Ni up to 4 per cent. In forming the alloy one or more of the elements may be added in the form of hydrides. The addition of monoazite to the melt ensures the production of a uniformly fine-pored material suitable for bearings. The resulting alloy may be cast by continuous casting, pressure or die casting from a melt at a temperature of 550-680 DEG C. Preferably the melt is cooled in stages first locally then as to the rest, as by use of a steel mandrel as a casting core which may be cooled by water or simply serve as a heat dissipator. The casting may be heat treated. For example it may be subjected to prolonged heating to 350-400 DEG C. for 6-12 hours and tempered and then quenched in cold sand impregnated with oil. Alternatively the incompletely cooled casting may be heated to 300-400 DEG C. on removing from the mould and placed successively in sand baths at various temperatures, e.g. 200 DEG C., 100 DEG C. and 10-20 DEG C., for several hours in each. Chill mould castings may be tempered at 250-300 DEG C. then cooled to 10-20 DEG C. in sand. Specifications 769,484 and 769,485 are referred to.