Apparatus for producing metal to be semimolten-molded

Details Apparatus for producing metal to be semimolten-molded Apparatus for producing metal to be semimolten-molded

1999-04-05

2000-12-26

Kastler, Scott

Metallurgical apparatus

With cleaning or lubricating means

266241, 266242, 164312, B22D 1708, B22D 2300, B22D 2700

Patent

active

061654116

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to an apparatus for producing semisolid shaping metals. More particularly, the invention relates to an apparatus with which semisolid metals suitable for semisolid shaping that have fine primary crystals dispersed in the liquid phase and that have a uniform temperature distribution can be produced in a very convenient and easy way.


BACKGROUND ART

A thixo-casting process is drawing researcher's attention these days since it involves a fewer molding defects and segregations, produces uniform metallographic structures and features longer mold lives but shorter molding cycles than the existing casting techniques. The billets used in this molding method (A) are characterized by spheroidized structures obtained by either performing mechanical or electromagnetic agitation in temperature ranges that produce semisolid metals or by taking advantage of recrystallization of worked metals.
On the other hand, raw materials cast by the existing methods may also be molded in a semisolid state. There are three examples of this approach; the first two concern magnesium alloys that will easily produce an equiaxed microstructure and Zr is added to induce the formation of finer crystals [method (B)] or a carbonaceous refiner is added for the same purpose [method (C)]; the third approach concerns aluminum alloys and a master alloy comprising an Al-5% Ti-1% B system is added as a refiner in amounts ranging from 2-10 times the conventional amount [method (D)]. The raw materials prepared by these methods are heated to temperature ranges that produce semisolid metals and the resulting primary crystals are spheroidized before molding.
It is also known that alloys within a solubility limit are heated fairly rapidly up to a temperature near the solidus line and, thereafter, in order to ensure a uniform temperature distribution through the raw material while avoiding local melting, the alloy is slowly heated to an appropriate temperature beyond the solidus line so that the material becomes sufficiently soft to be molded [method (E)]. A method is also known, in which molten aluminum at about 700.degree. C. is cast to flow down an inclined cooling plate to form partially molten aluminum, which is collected in a vessel [method (F)].
These methods in which billets are molded after they are heated to temperatures that produce semisolid metals are in sharp contrast with a rheo-casting process (G), in which molten metals containing spherical primary crystals are produced continuously and molded as such without being solidified to billets. It is also known to form a rheo-casting slurry by a method in which a metal which is at least partially solid, partially liquid and which is obtained by bringing a molten metal into contact with a chiller and inclined chiller is held in a temperature range that produces a semisolid metal [method (H)].
Further, a casting apparatus (I) is known which produces a partially solidified billet by cooling a metal in a billet case either from the outside of a vessel or with ultrasonic vibrations being applied directly to the interior of the vessel and the billet is taken out of the case and shaped either as such or after reheating with r-f induction heater.
However, the above-described conventional methods have their own problems. Method (A) is cumbersome and the production cost is high irrespective of whether the agitation or recrystallization technique is utilized. When applied to magnesium alloys, method (B) is economically disadvantageous since Zr is an expensive element and speaking of method (C), in order to ensure that carbonaceous refiners will exhibit their function to the fullest extent, the addition of Be as an oxidation control element has to be reduced to a level as low as about 7 ppm but then the alloy is prone to burn by oxidation during the heat treatment just prior to molding and this is inconvenient in operations.
In the case of aluminum alloys, about 500 .mu.m is the crystal grain size that can be achieved by the mere addition of refiners and it is not eas

REFERENCES:
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patent: 5533562 (1996-07-01), Moschini et al.
patent: 5697425 (1997-12-01), Nanba et al.
patent: 5701942 (1997-12-01), Adachi et al.
patent: 5730198 (1998-03-01), Sircar
patent: 5758707 (1998-06-01), Jung et al.

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