Manufacturing method of aluminum alloy in which Al—Fe—Si compound is refined

Abstract

A manufacturing method of an inexpensive aluminum alloy that allows fine crystallization of the AlFeSi compound and primary Si by employing a convenient and efficient means. To a molten aluminum alloy including 8 to 20% by mass of Si; 0.5 to 4% by mass of Fe; and, as necessary, at least any one of Mn and Cr; at least any one of Ni, Cu, and Mg; P; and the balance being Al and impurities, AlB.sub.2, which is present as a solid phase in molten metal upon crystallization of the AlFeSi compound, is added in such an amount that B is in a range of 0.01 to 0.5% by mass with respect to entire molten aluminum alloy. As the AlB.sub.2, an AlB alloy which includes B as the AlB.sub.2 may be used.

Claims

1. A manufacturing method of an aluminum alloy in which an AlFeSi compound is refined, comprising adding, to a molten aluminum alloy comprising 8 to 20% by mass of Si; 0.5 to 4% by mass of Fe; with the balance being Al and impurities, AlB.sub.2, which is present as a solid phase in the molten metal upon crystallization of the AlFeSi compound, in an amount of 0.02 to 1.2% by mass with respect to the entire molten aluminum alloy so that B is in a range of 0.01 to 0.5% by mass with respect to the entire molten aluminum alloy, wherein the AlB.sub.7 is contained in an AlB alloy, and the AlB alloy is added to the molten aluminum alloy.

2. The manufacturing method of an aluminum alloy in which an AlFeSi compound is refined according to claim 1, wherein the AlB alloy further comprises 0.003 to 0.015% by mass of TiB.sub.2.

3. The manufacturing method of an aluminum alloy in which an AlFeSi compound is refined according to claim 1, wherein the molten aluminum alloy further comprises at least one of 0.005 to 2.5% by mass of Mn and no greater than 0.5% by mass of Cr.

4. The manufacturing method of an aluminum alloy in which an AlFeSi compound is refined according to claim 1, wherein the molten aluminum alloy further comprises at least one of 0.5 to 6% by mass of Ni, 0.5 to 8% by mass of Cu, and 0.05 to 1.5% by mass of Mg.

5. The manufacturing method of an aluminum alloy in which an AlFeSi compound is refined according to claim 1, wherein the molten aluminum alloy further comprises 0.003 to 0.02% by mass of P.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram (1) illustrating metallographic structures of aluminum alloys produced in Examples and Comparative Examples;

(2) FIG. 2 is a diagram (2) illustrating metallographic structures of aluminum alloys produced in Examples and Comparative Examples;

(3) FIG. 3 is a diagram (3) illustrating metallographic structures of aluminum alloys produced in Examples and Comparative Examples;

(4) FIG. 4 is a diagram (4) illustrating metallographic structures of aluminum alloys produced in Examples and Comparative Examples;

(5) FIG. 5 is a diagram (5) illustrating metallographic structures of aluminum alloys produced in Examples and Comparative Examples; and

(6) FIG. 6 is a diagram (6) illustrating metallographic structures of aluminum alloys produced in Examples and Comparative Examples.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

(7) The present inventors have conducted extensive research with regard to a method of preventing coarsening and allowing fine crystallization of an AlFeSi crystallization product which crystallizes in a process of cooling and solidification of molten metal during production of an aluminum alloy containing large amounts of Si and Fe.

(8) Given that an effect of refining the AlFeSi crystallization product was obtained in the method proposed in Patent Document 1, constituent elements of the AlFeSi crystallization product being refined by ultrasonic radiation were investigated, and it was proven that CrSi.sub.2 and TiSi.sub.2 were solidification nuclei of the AlFeSi compound. In addition, it was proven that the AlFeSi compound is refined also by adding a silicide containing CrSi.sub.2 and TiSi.sub.2 in the method proposed in Patent Document 2.

(9) CrSi.sub.2 and AlB.sub.2 in Patent Document 2 are of the same crystalline system. Given this, it was presumed that AlB.sub.2, which is included as a solid phase upon crystallization of the AlFeSi compound, would act as a solidification nucleus of the AlFeSi compound and a refinement effect of crystallization product would be obtained, leading to completion of the present invention.

(10) AlB.sub.2 is present in the molten metal as a solid phase for a certain amount of time and acts as a nucleus for crystallization of the AlFeSi compound, since the melting point thereof is higher than the crystallization temperature of the AlFeSi compound. However, after holding for an extended period of time, AlB.sub.2 ultimately dissolves. Once dissolved, AlB.sub.2 does not necessarily recrystallize at a higher temperature than the AlFeSi compound. In such a case, the AlFeSi compound is without a nucleus. For improvement of high temperature stability of AlB.sub.2, upon production of an AlB alloy, crystallizing AlB.sub.2 with TiB.sub.2, which has been added in advance, as a solidification nucleus is effective. Since TiB.sub.2 is fine particle which can present in molten aluminum alloy as a solid phase even in a small quantity, high temperature stability of AlB.sub.2 having this as solidification nuclei is improved.

(11) The present invention is described in detail hereafter.

(12) First, components and composition ranges of the molten aluminum alloy are described.

(13) Si: 8 to 20% by Mass

(14) Si is an element that is essential for improving stiffness and abrasion resistance and for reducing thermal expansion of the aluminum alloy, and is included in an amount in a range of 8 to 20% by mass. An amount smaller than 8% by mass results in poor castability. An amount exceeding 20% by mass results in extremely high crystallization temperature of Si and requires higher melting temperature and casting temperature. This increases a gas volume in the molten metal and causes a casting defect. The rise of casting temperature may lead to a shorter life of a fireproof material.

(15) Fe: 0.5 to 4% by Mass

(16) Fe crystallizes as the AlFeSi compound and increases stiffness and reduces thermal expansion of the aluminum alloy. The Fe content lower than 0.5% by mass does not provide a sufficient amount of the AlFeSi crystallization product required for increase of stiffness, and the Fe content higher than 4% by mass coarsens the crystal particles and deteriorates processability. The Fe content exceeding 4% by mass results in high crystallization temperature of the AlFeSi compound and requires higher casting temperature. This increases a gas volume in the molten metal and causes a casting defect. The rise of casting temperature may lead to a shorter life of a fireproof material.

(17) Mn: 0.005 to 2.5% by Mass

(18) Mn is an element that crystallizes as an Al(Fe, Mn)Si compound and has an effect of agglomerating an acicular and coarse AlFeSi crystallization product, contained as necessary. The Fe amount exceeding 1% by mass results in a problem of the AlFeSi compound becoming acicular and coarse. In such a case, addition of Mn in an amount of 0.5 to 0.6 times of the Fe amount is effective for agglomeration. In a case in which the Fe amount is smaller than 1% by mass, Mn can be added in an amount of 0.005 to 0.6% by mass regardless of the Fe amount. However, the amount greater than 2.5% by mass accelerates coarsening. In addition, the crystallization temperature of the Al(Fe, Mn)Si compound rises and higher melting temperature and higher casting temperature are required. This increases a gas volume in the molten metal and causes a casting defect. The rise of casting temperature may lead to a shorter life of a fireproof material.

(19) Cr: No Greater than 0.5% by Mass

(20) Cr is an element that crystallizes as an Al(Fe, Mn, Cr)Si compound and has an effect of agglomerating an acicular and coarse AlFeSi crystallization product, and is contained as necessary. However, the amount greater than 0.5% by mass raises the crystallization temperature of the Al(Fe, Mn, Cr)Si compound and requires higher melting temperature and higher casting temperature. This increases a gas volume in the molten metal and causes a casting defect. The rise of casting temperature may lead to a shorter life of a fireproof material.

(21) P: 0.003 to 0.02% by Mass

(22) P functions as a refining agent of primary Si. Content of 0.003% by mass is necessary for exertion of its function. However, addition in an amount exceeding 0.02% by mass deteriorates fluidity and may cause casting defects such as misrun. Given this, an upper limit of the P content is 0.02%. Especially in a case in which Si is in an amount greater than 11.5% by mass, it is preferable that 0.003 to 0.02% by mass of P is contained.

(23) Ni: 0.5 to 6% by Mass

(24) In a state in which Cu is present, Ni crystallizes as an AlNiCu compound and has an effect of increasing stiffness and reducing thermal expansion, and is added as necessary. This also improves high temperature strength. An effect of this function is exerted especially with an amount greater than 0.5% by mass; an amount exceeding 6.0% by mass raises the liquidus temperature and deteriorates castability. Given this, the added amount of Ni is preferably in a range of 0.5 to 6.0% by mass.

(25) Cu: 0.5 to 8% by Mass

(26) Cu has a function of improving the mechanical strength and is added as necessary. Cu, in a form of an AlNiCu compound, also improves stiffness and reduces thermal expansion. This also improves high temperature strength. This function becomes remarkable with addition in an amount of at least 0.5% by mass; however, if the amount exceeds 8% by mass, coarsening of compound progresses, and mechanical strength and corrosion resistance deteriorate. Given this, the added amount of Cu is preferably in a range of 0.5 to 8% by mass.

(27) Mg: 0.05 to 1.5% by Mass

(28) Mg is an alloy element which is effective for improving strength of the aluminum alloy, and is added as necessary. Addition of Mg in an amount of at least 0.05% by mass can provide the above described effect; however, the amount exceeding 1.5% by mass hardens a matrix and deteriorates toughness and is therefore not preferable. Given this, the added amount of Mg is preferably in a range of 0.05 to 1.5% by mass.

(29) Configurations, added amounts, and the like of substances, which are added to molten aluminum alloy and act as solidification nuclei upon crystallization of the AlFeSi compound, are described hereafter.

(30) To molten aluminum alloy of composition ranges of elements adjusted as described above, AlB.sub.2, which is present as a solid phase in the molten metal upon crystallization of the AlFeSi compound, is added in such an amount that B is in a range of 0.01 to 0.5% by mass with respect to the entire molten aluminum alloy. The amount is equivalent to 0.02 to 1.2% by mass of AlB.sub.2. AlB.sub.2 acts as solidification nuclei upon crystallization of the AlFeSi compound and allows fine crystallization of the AlFeSi compound. A calculated value of the amount of AlB.sub.2 less than 0.02% by mass does not provide this effect and a value exceeding 1.2% by mass increases viscosity of the molten metal and deteriorates fluidity.

(31) It is preferable that AlB.sub.2 is added to the molten aluminum alloy in a form of AlB alloy. For example, Al-0.5 mass % B alloy, Al-3 mass % B alloy, Al-4 mass % B alloy, and the like can be used. B in these alloys is generally in a form of AlB.sub.2. A refinement effect of AlB.sub.2 continues for around 30 minutes and it is therefore preferable to cast the metal within 30 minutes after addition thereof. For extension of the refinement effect, it is preferable to use an alloy to which 0.003 to 0.015% by mass of TiB.sub.2 has been added as the AlB alloy in advance. In this alloy, AlB.sub.2 crystallizes with TiB.sub.2 as solidification nuclei, and AlB.sub.2 functions effectively as nuclei for an extended period of time. In this case, the refinement effect of AlB.sub.2 continues for at least 1 hour.

(32) Addition of AlB.sub.2 is not limited to the above described method, as long as it can be present as a solid phase upon crystallization of the AlFeSi compound.

EXAMPLES

(33) Molten aluminum alloy of a component composition shown in Table 1 was prepared by using: Al-25 mass % Si alloy; Al-5 mass % Fe alloy; Al-10 mass % Mn alloy; Al-5 mass % Cr alloy; Al-20 mass % Ni alloy; Al-30 mass % Cu alloy; pure Si; pure Fe; pure Cu; pure Mg; and Al-19 mass % Cu-1.4 mass % P alloy.

(34) B in Examples 1 to 7 was added by slicing an Al-4 mass % B alloy ingot manufactured by Fukuoka Alumi Industry Co., Ltd. In Example 8, B was added in a form of an Al-0.5 mass % alloy (manufactured by inventors) containing 0.007% by mass of TiB.sub.2.

(35) CrSi.sub.2 in Comparative Example 5 was added in a form of CrSi.sub.2 powder of 2 to 5 m in average particle size (product ID: CrSi.sub.2F) manufactured by Japan New Metals Co., Ltd.

(36) Retention time between addition of the refining agent and casting was: 30 minutes in Examples 1 to 7; 70 minutes in Example 8; and 30 minutes in Comparative Example 5. Die casting and gravity casting were employed as casting methods; in every case, cooling rate was 10.sup.2 C./s (die casting: plate of thickness 6 or 10; gravity casting using a copper mold: round bar of 10). Casting temperature was almost equal in a range of 760 to 770 C. Die temperature was also almost equal in a range of 100 to 130 C.

(37) FIGS. 1 to 6 are micrographs illustrating metallographic structures of aluminum alloys produced in Examples 1 to 8 and Comparative Examples 1 to 7. In micrographs of FIGS. 1 to 6, gray portions represent the AlFeSi compound and black portions represent pure Si crystals.

(38) Example 1 and Comparative Example 1 used alloys of the same composition as samples, Example 1 being added with AlB.sub.2. In Comparative Example 1, no AlFeSi compound which is remarkably coarse is present; however, Example 1 is finer.

(39) Example 2 and Comparative Example 2 used alloys of almost the same composition as samples. Example 2, to which B is added, is finer.

(40) Example 3 and Comparative Example 3 used alloys of the same composition as samples. Example 3, to which B is added, is finer.

(41) Example 4 and Comparative Examples 4, 5 used alloys of almost the same composition as samples. Example 4, to which B is added, is finer than Comparative Example 4 without B. Example 4 and Comparative Example 5 are equivalent structures; however, in Comparative Example 5, addition of a powdery refining agent was difficult and the powdery refining agent was not sufficiently dispersed in the molten metal even after stirring of the molten metal, and generally, in a case of addition in a powdery form, only about 10% was well blended with the molten metal.

(42) Example 5 and Comparative Example 6 used alloys of the same composition as samples. Example 5, to which 0.4% by mass of B is added, is finer.

(43) Examples 6, 7 and Comparative Example 7 used alloys of the same composition as samples. In Examples 6, 7 in which 0.04% by mass and 0.01% by mass of B are respectively added, refined AlFeSi compositions are obtained.

(44) In Example 8, B was added in a form of an AlBTiB.sub.2 alloy. As a result, an AlFeSi compound, which is fine even for a retention time of 1 hour or more, was obtained.

(45) The above results show that the AlFeSi compound is refined by adding AlB.sub.2 to molten aluminum alloy, and that continuation time of the refinement effect is extended by using the AlBTiB.sub.2 alloy as a refining agent.

(46) TABLE-US-00001 TABLE 1 Component Compositions, Manufacturing Conditions. AlFeSi State, and Ease of Addition of Refining Agent of Aluminum Alloy Material Sample Amount of Manufacturing Condition Ease of Addition of Casting Addition Refining Agent Retention Tempera- of Alloy Composition (mass %) (mass %) Time Casting ture AlFeSi Refining Si Fe Mn Cr Ni Cu Mg P B alone AlB.sub.2 CuSi.sub.2 (min) Method ( C.) State Agent Example 1 90 0.5 0.3 0.03 0.07 3.0 Die Casting 770 Fine Easy 2 110 2.5 1.5 2.5 4.0 0.5 1.12 3.0 Die Casting 760 Fine Easy 3 170 3.0 1.8 0.5 0.01 0.03 0.06 3.0 Gravity 770 Fine Easy Casting 4 180 3.5 2.0 0.5 0.01 0.01 0.09 3.0 Gravity 770 Fine Easy Casting 5 200 4.0 2.0 0.5 0.01 0.4 0.90 3.0 Gravity 770 Fine Easy Casting 6 185 3.8 1.9 0.3 2.5 0.2 0.01 0.04 0.09 3.0 Die Casting 770 Fine Easy 7 185 3.8 1.9 0.3 2.5 0.2 0.01 0.01 0.02 3.0 Die Casting 770 Fine Easy 8 170 3.0 1.8 0.3 0.5 0.01 0.02 0.05 7.0 Gravity 770 Fine Easy Casting Com- 1 90 0.5 0.3 <0.005 Die Casting 770 Coarser than N/A parative Example 1 Example 2 130 2.5 1.5 2.5 4.0 0.01 <0.005 Die Casting 760 Coarser than N/A Example 2 3 170 3.0 1.8 0.5 0.01 <0.005 Gravity 770 Coarser than N/A Casting Example 3 4 180 3.5 2.0 0.5 0.01 <0.005 Gravity 770 Coarser than N/A Casting Example 4 5 186 3.8 2.0 0.25 0.1 0.01 <0.005 0.1 3.0 Gravity 770 Equal to Difficult Casting Example 4 6 200 4.0 2.0 0.5 0.01 <0.005 Gravity 770 Coarser than N/A Casting Example 5 7 185 3.8 1.9 0.3 2.5 0.2 0.01 <0.005 Die Casting 770 Coarser than N/A Example 6, 7