Gm Global Technolgoy Operations, Inc.

Venkatasubramanian Laxmanan

Suresh Deepchand Shah

Jayprakash Uttamchand Raisoni

Robert James Hoye

High strength to weight ratio, improved dimensional and surface quality hollow metal moldings are formed by injecting thixotropic, semi-solid metal billets as a 'short shot' into a mold cavity; introducing an inert gas into the charge under pressure to force the metal into full and faithful contact with cavity surfaces and to form a hollow portion in the molding; maintaining the pressure of the gas on the charge in the cavity until the metal has solidified and then venting the gas for molded product removal.

Gas-assisted molding of thixotropic semi-solid metal alloy

A semi-solid metal-forming process for producing an article of a hypoeutectic aluminum-silicon alloy comprises heating a solid billet of the alloy to a temperature intermediate the liquidus temperature and the solidus temperature at a rate not greater than 30.degree. C. per minute, preferably not greater than 20.degree. C. per minute, to form a semi-solid body of the alloy while inhibiting the formation of free silicon particles therein. The semi-solid body comprises a primary spheroidal phase dispersed in a eutectic-derived liquid phase and is conducive to forming at low pressure. In one apsect of this invention, a billet having a quiescently cast microstructure characterized by primary dendrite particles in a eutectic matrix is heated at the slow rate and maintained at the intermediate temperature for a time sufficient to transform the dendrite phase into the desired spheroidal phase.

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Troy, MI, United States of America

Venkatasubramanian Laxmanan