Metal treatment – Stock – Aluminum base
Reexamination Certificate
1999-04-13
2001-08-21
Ip, Sikyin (Department: 1742)
Metal treatment
Stock
Aluminum base
C420S542000, C420S543000, C420S547000
Reexamination Certificate
active
06277217
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an aluminum alloy for a tough, die-cast product and particularly, an Al—Mg—Mn—Ni based alloy.
2. Description of the Related Art
Aluminum alloys are known from which a die-cast product having a relatively high strength in an as-cast state can be produced (for example, see Japanese Patent Application Laid-open No. 63-250438).
Attempts are presently being made to substitute die-cast products made of an aluminum alloy for various parts made of steel due to a demand for decreasing the weight of a motorcycle. In this case, the die-cast product must have not only high strength but also excellent shock resistance, that is, the die-cast product should have a high toughness for the reason that various parts are exposed to the outside.
It is also required that when the die-cast product is subjected to an anode oxidizing treatment in order to enhance the appearance quality of the motorcycle, the film formed on the resulting product should be aesthetically appealing.
A conventional die-cast product made of aluminum alloy has the advantages that it can be placed into use in an as-cast state, thermal treatment can be eliminated to enhance productivity and production costs can be reduced. However, the conventional die-cast product suffers from the problem that because the Ni content is as high as in the range of 1% by weight≦Ni≦5.5% by weight, grains of an acicular intermetallic compound, AlMnNi, are liable to be coalesced, and due to this, the toughness of the die-cast product is relatively low, and the aesthetic aspect of the film formed by the anode oxidizing treatment may also be reduced.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an aluminum alloy of the above-described type, from which a die-cast product having a high toughness in an as-cast state and an aesthetically appealing film formed by an anode oxidizing treatment can be produced by regulating, particularly, the Ni content.
To achieve the above object, according to the present invention, there is provided an aluminum alloy for a die-cast product having a high toughness, comprising magnesium in a range of 3.0% by weight≦Mg≦5.5% by weight, manganese in a range of 1.5% by weight≦Mn≦2.0% by weight, nickel in a range of 0.5% by weight≦Ni≦0.9% by weight, and the balance of aluminum including inevitable impurities.
The die-cast product made of the aluminum alloy having a composition as described above has a high toughness and a predetermined strength in the as-cast state. By subjecting the die-cast product to an anode oxidizing treatment, an aesthetically appealing film can be formed in the die-cast product.
Furthermore, the molten metal of aluminum alloy has an excellent castability in that the seizure or adhesion of the molten metal to a mold is inhibited; the molten metal has a good flowability and moreover, the number of points of cracks generated in the die-cast product is small.
The function and effect of the chemical constituents and the basis for the inclusion of the chemical constituents will be described below.
Magnesium (Mg): It has an effect that when it is incorporated as a solid-solution into &agr;-aluminum (&agr;-Al), it enhances the strength of the matrix formed. However, if the Mg content is lower than 3.0% by weight, the strength of the matrix cannot be enhanced sufficiently. On the other hand, if the Mg content is higher than 5.5% by weight, the die-cast product has an increased tensile strength, but has a reduced impact value, namely, a reduced toughness. Regarding castability, if the Mg content is low, e.g., in a range of 1.0 to 2.0% by weight, the crack sensitiveness is remarkably high. On the other hand, if the Mg content is high, e.g., 6.0% by weight, the molten metal is violently oxidized, resulting in a deteriorated flowability.
Manganese (Mn): It produces an intermetallic compound, AlMgMn, at an initial stage of solidification of the molten metal. A liquid-phase state permitting the flow of &agr;-Al is maintained for a relatively long period by a large latent heat of solidification of the intermetallic compound and hence, the flowability of the molten metal is improved. Manganese also has the effect of inhibiting the seizure or adhesion of the molten metal to the mold. Furthermore, manganese is incorporated as a solid solution into the &agr;-Al under a quenching provided by the die-casting, whereby the strength of the matrix is enhanced, and an intermetallic compound, Al
6
Mn, is dispersed finely and crystallized. Therefore, the toughness and strength of the die-cast product are enhanced. However, if the Mn content is lower than 1.5% by weight, the effect of enhancing the flowability of the molten metal and the seizure inhibiting effect are not obtained sufficiently. On the other hand, if the Mn content is higher than 2.0% by weight, the grains of the intermetallic compound Al
6
Mn are coalesced. For this reason, the die-cast product has a reduced toughness.
Nickel (Ni): In the course of pouring the molten metal into the mold, nickel (Ni) produces a eutectic crystal, Al
3
Ni, when the &agr;-Al is crystallized. The eutectic crystal, Al
3
Ni, assumes a liquid phase state between adjacent &agr;-Al crystals and hence, the propagation of an injecting pressure is easily performed, whereby the cracking of the die-cast product attendant with the solidification and shrinkage of the molten metal can be reduced. Nickel also has the effect of inhibiting the seizure of the molten metal to the mold, as does manganese. However, if the Ni content is lower than 0.5% by weight, the propagation of the injecting pressure is insufficient. On the other hand, if the Ni content is higher than 0.9% by weight, the grains of the acicular intermetallic compound AlMnNi are liable to be produced in a large amount and to be coalesced. For this reason, the elongation and the impact value of the die-cast product are reduced, and the aesthetic attributes of the film formed by the anode oxidizing treatment is also reduced.
Silicon (Si) and iron (Fe): During production of an aluminum alloy and in a die-casting process of forming a product of the aluminum alloy, silicon (Si) and iron (Fe) are inevitably incorporated impurities. The silicon promotes the seizure or adhesion of the molten metal to the mold and is segregated on the surface of the die-cast product, thereby reducing the aesthetic attributes of the film formed by the anode oxidizing treatment. On the other hand, iron (Fe) promotes the production of an intermetallic compound which exerts an adverse effect on the mechanical strength of the die-cast product. Therefore, it is desirable that the Si and Fe concentrations be reduced to the utmost.
In addition, according to the present invention, the aluminum alloy for the die-cast product having improved toughness further includes at least one of titanium (Ti) in a range of 0.1% by weight ≦Ti≦0.2% by weight and beryllium (Be) in a range of 0.001% by weight≦Be≦0.006% by weight in addition to the above-described chemical constituents in order to improve the castability further.
Titanium (Ti) produces an intermetallic compound Al
3
Ti which acts as an &agr;-aluminum producing nucleus in a thick portion of the die-cast product to produce a fine texture, whereby cracking of the die-cast product is inhibited. However, if the Ti content is lower than 0.1% by weight, the intermetallic compound Al
3
Ti is not produced in sufficient amounts. On the other hand, if the Ti content is higher than 0.2% by weight, the grains of the intermetallic compound Al
3
Ti are coalesced to exert an adverse affect on the toughness of the die-cast product.
Beryllium (Be) has the effect of preventing the oxidation of the molten metal, thereby inhibiting the dissipation of magnesium due to oxidation and the production of an oxide in the molten metal. To provide this effect reliably, the Be content is set in the above-described range.
The above and other objects, features and advantages of the invention wil
Koike Seiichi
Koya Eitarou
Nakagawa Masahiko
Yoshino Sadafumi
Arent Fox Kintner & Plotkin & Kahn, PLLC
Honda Giken Kogyo Kabushiki Kaisha
Ip Sikyin
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