Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
1999-02-02
2001-09-04
Lin, Kuang Y. (Department: 1722)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S312000, C072S462000, C428S472100, C428S472200
Reexamination Certificate
active
06283195
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to tooling for handling molten and hot solid aluminum and its alloys in manufacture of products therefrom.
BACKGROUND OF THE INVENTION
In the making of metal matrix composites (MMC's) comprising fine ceramic (e.g. alumina) reinforcement particles dispersed in a matrix comprising aluminum or its alloys, a semi-solid slurry (a thixotropic liquid/solid mixture) of the aluminum matrix material is formed in a refractory crucible, and the ceramic reinforcement particles are introduced into the aluminum slurry and mechanically mixed therein by a rotating mixing blade. Introduction of the ceramic reinforcement particles into the semi-solid aluminum slurry enables a high volume percentage, such as 30-40 volume %, of reinforcement particles to be dispersed in the aluminum matrix of the final MMC. Such an MMC process is described in the Flemings U.S. Pat. No. 3,948,650.
The mixing blade used to mechanically mix the ceramic reinforcement particles into the semi-solid aluminum slurry is subjected to tremendous abrasive action from the ceramic particles as they are dispersed in the semi-solid slurry. Expensive flame sprayed alumina coated stainless steel (Type 304) mixing blades used in the past typically exhibit catastrophic wear after only 30 minutes such that replacement with a new mixing blade is required.
There is a need for improved mixing blades for use in the manufacture of MMC's using semi-solid slurries as well in other manufacturing applications that process or handle molten or hot solid aluminum and its alloys.
An object of the present invention is to satisfy this need.
SUMMARY OF THE INVENTION
The present invention provides in one embodiment tooling for handling molten or hot solid aluminum and its alloys wherein the tooling comprises passivated titanium aluminide (TiAl) intermetallic compound having a thin passivating surface oxide film formed in-situ thereon by contact with an oxygen-bearing atmosphere at elevated temperature. The surface oxide film passivates and renders the tooling non-wetted by and non-reactive with molten aluminum and its alloys and non-bonded to hot solid aluminum and its alloys.
Passivated titanium aluminide intermetallic tooling having the thin surface oxide film formed in-situ thereon can comprise a mixing blade for making MMC's in the manner described above and also can comprise other tooling. For example, passivated titanium aluminide intermetallic tooling having the thin surface oxide film formed in-situ thereon can comprise hot die casting machine components, such as hot shot sleeves, plungers and dies, hot extrusion die components such as extrusion dies, and holders for molten aluminum filters in permanent mold casting. The passivated titanium aluminide intermetallic tooling advantageously exhibits a coefficient of thermal expansion that is comparable to that of H13 tool steel such that the titanium aluminide intermetallic tooling can be inserted in or mated with larger tooling or machine components made of H13 tool steel to provide a local tooling component that is non-wetted or non-bonded by molten or hot solid aluminum and its alloys.
The above and other objects and advantages of the present invention will become more readily apparent from the following drawings taken in conjunction with the following detailed description.
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Behavior of Metal Alloys in the Semisolid State; Metallurgical Transactions A, vol. 22A, May 1991, pp. 957, 970-972, 981; M.C. Flemings.
Chandley George D.
Harrison Curtis A.
Zhao Qi
Lin Kuang Y.
Metal Casting Technology, Incorporated
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