Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
1999-03-26
2002-08-20
Elve, M. Alexandra (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S487000, C164S444000, C164S504000
Reexamination Certificate
active
06435263
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an agitated continuous casting process for an aluminum alloy.
2. Description of the Related Art
An aluminum alloy ingot made by an agitated continuous casting process is conventionally used, for example, as a thixocasting material. In a thixocasting process, the casting is carried out by utilizing the fluidity of a semi-molten casting material having solid and liquid phases coexisting therein and hence, it is an essential condition to finely divide a highly-melting crystallized product such as an initial crystal &agr;.
However, when a recycled material is used as a starting material from the resources-saving demand, the following problem is encountered: If the content of Cu, Mn, Ti or the like in the recycled material is large, an acicular intermetallic compound having a high melting point is crystallized in a coalesced manner and cannot be finely divided only by an electromagnetic agitating force.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an agitated continuous casting process of the above-described type for an aluminum alloy, wherein a hard primary crystallized product is crystallized by specifying the aluminum alloy composition of a molten metal, and not only an initial crystal &agr; but also an acicular intermetallic compound of high melting point can be finely divided by cooperation of the primary crystallized product with an electromagnetic agitating force.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided an agitated continuous casting process for an aluminum alloy, comprising continuously casting a molten metal of an aluminum alloy composition while applying an electromagnetic agitating force to the molten metal, wherein the molten metal of the aluminum alloy composition used has an Fe content in a range of 0.75% by weight ≦Fe<2% by weight.
If the Fe content in the molten metal of the aluminum alloy composition is specified in the above-described range, a hard Fe-based intermetallic compound is crystallized as a primary crystallized product at a temperature equal to or higher than a temperature of crystallization of an initial crystal a, and pulverizes and finely divides the initial crystal a and an acicular intermetallic compound, while being moved at random in a liquid phase by the electromagnetic agitating force.
However, if the Fe content is lower than 0.75% by weight, it is absurd or meaning less to add iron (Fe). On the other hand, if the Fe content is higher than 2% by weight, an Fe-based intermetallic compound is crystallized in an excessive amount, resulting in a remarkably reduced toughness of a produced continuous casting material.
The present inventors have forwarded researches for the agitated continuous casting process and consequently, have made clear that the amount of &agr;-intermetallic compound crystallized in the Fe-based intermetallic compound is increased depending on the Mn content in the molten metal, and the crystallized &agr;-intermetallic compound becomes a massive &agr;-intermetallic compound by its growth, thereby suppressing the crystallization of a fine &bgr;-intermetallic compound in the Fe-based intermetallic compound. The massive &agr;-intermetallic compound reduces the cutting property of a produced aluminum alloy member, and moreover, brings about a deterioration in plating property and a reduction in fatigue strength of the aluminum alloy member.
It is another object of the present invention to provide an agitated continuous casting process of the above-described type, wherein the amount of &agr;-intermetallic compound crystallized can be suppressed to an inevitable amount, and the amount of fine &bgr;-intermetallic compound crystallized can be increased to an upper limit value.
To achieve the above object, according to a second aspect and feature of the present invention, there is provided an agitated continuous casting process in which a molten metal of an aluminum alloy composition is introduced into a cylindrical water-cooled casting mold disposed immediately below a spout, while being agitated within the spout, wherein the molten metal of the aluminum alloy composition used has an Fe content in a range of 0.75% by weight ≦Fe<2% by weight, and an Mn content which is set at Mn≦[(Fe/5)+0.2]% by weight, when the Fe content is in a range of 0.75% by weight ≦Fe≦1.5% by weight; while being Mn≦[−Fe+2]% by weight, when the Fe content is in a range of 1.5% by weight <Fe<2% by weight; and the molten metal cooling speed CR in an upper peripheral edge of a molten metal agitating area forming portion on an inner peripheral surface of the spout is set in a range of 10° C./sec ≦CR≦30° C./sec.
If the Fe and Mn contents are set in the above-described ranges, the amount of &agr;-intermetallic compound crystallized can be suppressed to an inevitable amount. The upper peripheral edge is a site where the molten metal cooling speed is slowest. If the molten metal cooling speed CR in the upper peripheral edge is set in the above-described range, the growth of the &agr;-intermetallic compound can be suppressed. This enables the amount of fine &bgr;-intermetallic compound crystallized to be increased to an upper limit value to largely enhance the mechanical property of an aluminum alloy member. The cooling speed is calculated from a cooling curve established in the upper peripheral edge. The &agr;-intermetallic compound contributes to the pulverization and fine-dividing of a coalesced acicular intermetallic compound and an initial crystal &agr;.
However, if the Fe and Mn contents depart from the above-described ranges, the amount of &agr;-intermetallic compound crystallized tends to be increased. If the cooling speed CR is lower than 10° C./sec, the growth of the &agr;-intermetallic compound is advanced, whereby the fine &bgr;-intermetallic compound is difficult to crystallize, or is not crystallized. On the other hand, if the cooling speed CR is higher than 30° C./sec, the fine-dividing of the initial crystal a in an ingot is insufficient, and the rheologic property of the ingot, because the cooling speed is too high.
Further, the present inventors have forwarded the researches for the agitated continuous casting process and consequently, have investigated that the Fe-based intermetallic compounds are agglomerated in an outer peripheral area of an ingot to form a relatively large agglomerate, depending on the Mn content in the molten metal, and for this reason, it is impossible to provide a sufficient pulverizing and finely-dividing effect by the Fe-based intermetallic compounds in some cases.
The agglomerate is chemically stable and hence, it is difficult to finely divide the agglomerate by an added element. Moreover, the agglomerate has a high melting point and hence, it is difficult to disintegrate and finely divide the agglomerate by a thermal treatment. If a thixocasting is carried out using a casting material including such an agglomerate, the agglomerate is caught in an intact state within a produced aluminum alloy member. Therefore, the toughness, elongation and the like of the aluminum alloy member are remarkably reduced.
It is a further object of the present invention to provide an agitated continuous casting process of the above-described type, wherein the agglomeration of the Fe-based intermetallic compounds in an outer peripheral zone of an ingot made of the aluminum alloy can be suppressed to a large extent, and the segregation of various intermetallic compounds in a center zone of the ingot can be avoided.
To achieve the above object, according to a third aspect and feature of the present invention, there is provided an agitated continuous casting process in which a molten metal of an aluminum alloy composition is introduced into a cylindrical water-cooled casting mold disposed immediately below a spout, while being agitated within the spout, wherein the molten metal of t
Idegomori Takashi
Mizoue Kiyonobu
Nakamura Takeyoshi
Ohtani Teruyuki
Saito Nobuhiro
Elve M. Alexandra
Honda Giken Kogyo Kabushiki Kaisha
McHenry Kevin
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