Abstract: Milled silica or alumina fibres or whiskers are formed into a reinforcement for a squeeze cast article such as a piston for an internal combustion engine. The problem of handling the milled fibres or whiskers while they are formed into the reinforcement is mitigated or overcome by the use of coagulated latex to bind the milled fibres or whiskers in a colloidal silica solution until they are fired to form the reinforcement. In addition, a starch is used to prevent the milled fibres or whiskers settling when in the colloidal silica solution.

Abstract: A piston is manufactured by incorporating a reinforcement which is formed at least in part by a fibre material and which is so non-uniform as to provide differing characteristics in the cast piston in predetermined differing regions of the piston. For example, the volumetric density of the fibres may be different in one region of the reinforcement as compared with another region in order to produce a more resistant region in the cast piston. Additionally or alternatively, the reinforcement may hold finely divided materials which combine with the piston material during casting to give improved properties. Examples of this are the incorporation of particles of silicon, silicon carbide or silicon nitride to improve wear and/or the incorporation of molybdenum disulphide and tungsten disulphide or graphite to improve lubrication.

Abstract: A composition of matter comprises aluminium or aluminium alloy, such as LM 13, into which has been incorporated between 5 and 50% by volume of zirconia. The zirconia may be in the form of fibres or of powder. As compared with the aluminium alloy, this reduces the thermal conductivity and coefficient of expansion, and provides a material which has, particularly at elevated temperatures above 300.degree. C., improved tensile strength, compressive strength, and hardness and reduced elongation.

Abstract: A metal ring of generally rectangular cross-section has its radially outer surface and its side surfaces treated by being stacked with its sides in contact with other rings in a chamber. Air is excluded from the chamber and a gaseous mixture of a carburizing gas and a nitrogenous gas at a temperature of 450.degree. C. to 650.degree. C. is supplied to the chamber. The proportions (% by volume) of the gases is between 25:75 and 75:25. The mixture nitro-carburizes both the radially outer surface of the stacked rings and the sides of the ring. If the rings are finish machined before treatment, they are ready for use as soon as they are removed from the chamber. The nitro-carburizing treatment reduces wear on the treated surfaces. The rings are used as piston rings or sealing rings.