ALUMINUM ALLOY AND ALUMINUM ALLOY DIE CASTING MATERIAL

Abstract

Provided are a non-heat-treated aluminum alloy which has excellent casting properties and is high in both strength and toughness, and an aluminum alloy die casting material which is high in both strength and toughness, and which, in addition to having minimal difference in characteristics between regions thereof, is not prone to be affected by aging. An aluminum alloy comprises Si: 5.0 to 12.0% by mass, Mn: 0.3 to 1.9% by mass, Cr: 0.01 to 1.00% by mass, Ca: 0.001 to 0.050% by mass, with the balance being Al and unavoidable impurities, and the content of Mg in the unavoidable impurities being less than 0.3% by mass.

Claims

1. An aluminum alloy comprises Si: 5.0 to 12.0% by mass, Mn: 0.3 to 1.9% by mass, Cr: 0.01 to 1.00% by mass, Ca: 0.001 to 0.050% by mass, with the balance being Al and unavoidable impurities, and the content of Mg in the unavoidable impurities being less than 0.3% by mass.

2. The aluminum alloy according to claim 1, wherein the Cr content is 0.10 to 0.50% by mass.

3. The aluminum alloy according to claim 1, wherein Fe is 0.4% by mass or less in the unavoidable impurities.

4. The aluminum alloy according to claim 3, wherein Fe is 0.2% by mass or less.

5. An aluminum alloy die casting material comprising the aluminum alloy according to claim 1, which has a tensile property of 0.2% proof stress of 110 MPa or more and elongation of 10% or more.

6. The aluminum alloy die casting material according to claim 5, wherein, in the cross-sectional structure observation, an average value of the equivalent circle diameter of the eutectic Si structure is 3 μm or less, and a cross-sectional area ratio of the Cr-based crystallized product to the whole is 10% or less.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 shows an optical micrograph of the cross section of the example aluminum alloy die casting material 1.

[0035] FIG. 2 shows an optical micrograph of the cross section of the example aluminum alloy die casting material 2.

[0036] FIG. 3 shows an optical micrograph of the cross section of the example aluminum alloy die casting material 3.

[0037] FIG. 4 shows an optical micrograph of the cross section of the comparative example aluminum alloy die casting material 1.

EMBODIMENTS FOR ACHIEVING THE INVENTION

[0038] Hereinafter, typical embodiments of the aluminum alloy and the aluminum alloy die casting material of the present invention will be described in detail, but the present invention is not limited to these.

1. Aluminum Alloy

[0039] The aluminum alloy of the present invention contains Si: 5.0 to 12.0% by mass, Mn: 0.3 to 1.9% by mass, Cr: 0.01 to 1.00% by mass, Ca: 0.001 to 0.050% by mass, with the balance being Al and unavoidable impurities, and the content of Mg in the unavoidable impurities being less than 0.3% by mass. Hereinafter, each component will be described in detail.

(1) Additive Element

[0040] Si: 5.0 to 12.0% by Mass

[0041] Si has a function of improving the flow of molten metal to improve castability. When not reaching the lower limit, the castability becomes insufficient, and when exceeding the upper limit, since the formation of the crystallized product, which is the starting point of fracture, adversely affects the elongation, it is necessary to limit within the above range. In order to achieve both castability and elongation at a better level, Si: 7.0 to 12.0% by mass is preferable, and Si: 8.0 to 11.0% by mass is more preferable.

[0042] Mn: 0.3 to 1.9% by Mass

[0043] Mn must be contained in a certain amount in order to prevent the molten metal from being seized on the mold during casting. When being less than the lower limit of the specified range, the effect is not sufficient, and when exceeding the upper limit, primary crystals of Al—Mn compounds are generated, and since, if this forms coarse crystallized products, ductility is adversely affected, it is limited within the above range. In order to achieve both toughness and castability, the upper limit of Mn is preferably 1.4% by mass, more preferably 1.0% by mass, and most preferably 0.8% by mass.

[0044] Cr: 0.01 to 1.00 Mass %

[0045] Cr is dissolved in the matrix to mainly improve the proof stress. When being less than the lower limit, the effect is small, and when adding beyond the upper limit, though the adverse effect on proof stress is small, since coarse Cr-based crystallized product is formed which is the starting point of fracture due to stress concentration, this adversely affects the ductility, it is necessary to limit within the above range. In order to obtain the effect of solid solution strengthening more reliably, addition of 0.10% by mass or more is preferable. It should be noted that, with the addition of about 0.50% by mass, since crystallized products containing Cr, but not coarse, will appear, in this composition, the limit at which Cr contributes to the proof stress as a solid solution strengthening element is approximately this value. Since the addition of more than this is a factor of increasing the cost, the upper limit is preferably 0.50% by mass, more preferably 0.40% by mass.

[0046] Ca: 0.001 to 0.050% by Mass

[0047] Ca mainly contributes to elongation by refining the eutectic Si structure. When being less than the lower limit, the effect is small, and even when adding beyond the upper limit, there is no effect because the eutectic Si structure has already been sufficiently refined. Further, when containing excessively, the crystallized product becomes coarse and adversely affects the toughness. In addition, since the addition of Ca is a cost-increasing factor, it is necessary to limit the upper limit within the above range. Though the effect of improving the eutectic Si structure can be obtained by adding Sr, Sb, and Na, in the composition of the present invention, elongation tends to be slightly inferior to that of Ca.

[0048] In addition, one or more of Ti: 0.05 to 0.20% by mass, B: 0.005 to 0.100% by mass, and Zr: 0.05 to 0.20% by mass may be further added. Since Ti, B, and Zr mainly contribute to toughness by refining the structure, it is preferably added. When being less than the lower limit, the effect is small, and even when containing beyond the upper limit, it is already sufficiently finely divided and has no effect, and, in addition thereto, when adding excessively, it adversely affects ductility by forming the coarse crystallized products, therefore it is necessary to limit within the above range.

(2) Inevitable Impurities

[0049] Mg: less than 0.3% by Mass

[0050] The aluminum alloy of the present invention is expected to be used in situations and cases where the adverse effects of Mg described in the above PRIOR ARTS are undesired in the product. Accordingly, Mg needs to be regulated at a low level. In order to more reliably avoid the above adverse effects, the Mg content is preferably limited to less than 0.1% by mass, more preferably less than 0.08% by mass.

[0051] Fe: 0.4% by Mass or Less

[0052] Generally, Fe is often added for the purpose of preventing the molten metal from being seized onto the mold during casting. On the other hand, in the aluminum alloy of the present invention, the addition of Fe forms Al—Fe—Si compounds and Fe—Si compounds, which adversely affect the ductility. Accordingly, Fe is preferably regulated to 0.4% by mass or less, more preferably 0.2% by mass or less.

[0053] The method for producing the aluminum alloy of the present invention having the above composition is not particularly limited as long as the effect of the present invention is not impaired, and the molten aluminum alloy having the desired composition may be melted by various conventionally known methods.

[0054] Impurities such as hydrogen gas and oxides are mixed in the molten metal that is melted in the atmosphere, and when this molten metal is cast as it is, defects such as porosity are appeared during solidification, which results in inhibiting the toughness of the produced member. In order to prevent these defects, it is effective to perform bubbling with an inert gas such as nitrogen or argon gas after melting the molten metal and before die casting. The inert gas supplied from the lower part of the molten metal, when ascending, has the function of catching hydrogen gas and impurities in the molten metal and removing them to the surface of the molten metal.

2. Aluminum Alloy Die Casting Material

[0055] The aluminum alloy die casting material of the present invention is a die casting material made of the aluminum alloy of the present invention having a tensile property of 0.2% proof stress of 110 MPa or more and elongation of 10% or more.

[0056] Both excellent 0.2% proof stress and elongation of the aluminum alloy die casting material are basically realized by seriously optimizing the composition, and the desired tensile properties are obtained regardless of the shape and size of the aluminum alloy die casting material. Here, the 0.2% proof stress is preferably 115 MPa or more, and the elongation is preferably 15% or more.

[0057] Further, in the aluminum alloy die casting material of the present invention, it is preferable that the average value of the equivalent circle diameter of the eutectic Si structure is 3 μm or less, and the cross-sectional area ratio of the Cr-based crystallized product to the whole is 10% or less. Dou to this microstructure, the high proof stress and elongation can be obtained. At this time, the method for determining the average value in the equivalent circle diameter of the eutectic Si structure and the cross-sectional area ratio of the Cr-based crystallized product to the whole is not particularly limited, and the measurement may be performed by various conventionally known methods. For example, the size of the eutectic Si structure or the Cr-based crystallized product can be obtained by cutting the aluminum alloy die casting material, observing the obtained cross-sectional sample with an optical microscope or a scanning electron microscope, and calculating. Depending on the observation method, the cross-sectional sample may be subjected to mechanical polishing, buffing, electrolytic polishing, etching or the like.

[0058] The shape and size of the aluminum alloy die casting material are not particularly limited as long as the effects of the present invention are not impaired, and can be made to various conventionally known members. Examples of the member include a vehicle body structural member.

3. Method for Manufacturing Aluminum Alloy Die Casting Material

[0059] The aluminum alloy die casting material of the present invention is a die casting material made of the aluminum alloy of the present invention. The die casting method for obtaining the aluminum alloy die casting material is not particularly limited as long as the effects of the present invention are not impaired, and various conventionally known methods and conditions may be used, and in the following, an example of manufacturing conditions for the aluminum alloy for die casting will be described.

[0060] Since the aluminum alloy used as the raw material of the aluminum alloy die casting material of the present invention contains the element for the purpose of solid solution strengthening, it is necessary to pay attention to the cooling rate in the production of the die casting material. When the cooling rate at the time of casting is slow, Mn, Cr and Ca cannot be sufficiently solid-solved in the matrix, and therefore, it is preferable to secure a cooling rate of 50° C./sec or more at the time of casting. At this time, the casting pressure may be set from 50 MPa to 150 MPa.

[0061] Further, in the manufacturing of a member using the die casting method, since the molten metal is poured into the mold at high pressure and high speed, there is a case that air in the mold is involved in the molten metal, or a case that due to solidification shrinkage, defects such as bubbles, and nests are occur in the member. Since the presence of many such defects adversely affects the toughness of the member, it is preferable to take technical measures to reduce these defects during casting.

[0062] Further, the aluminum alloy for die casting of the present invention is a non-heat treatable type aluminum alloy, and does not require heat treatment on the product after casting in order to obtain the mechanical properties required for, for example, the vehicle members in the die casting material. As a result, it is possible to reduce the cost related to the heat treatment step and the correction of the strain generated by the heat treatment step.

[0063] Although the typical embodiments of the present invention have been described above, the present invention is not limited to these, and various design changes are possible, and all of these design changes are included in the technical scope of the present invention.

EXAMPLES

Example 1

[0064] After melting the aluminum alloy having the composition shown in Example 1 in TABLE 1, the example aluminum alloy die casting material 1 was obtained by die casting. The values in TABLE 1 are % by mass, and the balance is Al.

TABLE-US-00001 TABLE 1 Si Mn Ti Fe Ca Cr Mg Ex.1 9.7 0.53 0.15 0.12 0.010 0.19 — Ex.2 9.2 0.48 0.14 0.13 0.010 0.45 — Ex.3 9.4 0.49 0.13 0.12 0.008 0.73 — Com. Ex.1 9.5 0.49 0.08 0.10 0.010 — — Com. Ex.2 9.5 0.48 0.09 0.15 0.006 — 0.43

[0065] As a die casting method, a non-porous die casting method was adopted to produce a die casting material. The size of the mold used at this time was 110 mm×110 mm×3 mm, the casting was conducted under the condition that the casting pressure at the time of die casting was 120 MPa, the molten metal temperature was 730° C., and the mold temperature was 160° C. A water-soluble release agent was used.

Example 2

[0066] An example aluminum alloy die casting material 2 was obtained in the same manner as in Example 1 except that the aluminum alloy having the composition shown in Example 2 in TABLE 1 was melted.

Example 3

[0067] An example aluminum alloy die casting material 3 was obtained in the same manner as in Example 1 except that the aluminum alloy having the composition shown in Example 3 in TABLE 1 was melted.

Comparative Example 1

[0068] A comparative aluminum alloy die casting material 1 was obtained in the same manner as in Example 1 except that the aluminum alloy having the composition shown as Comparative Example 1 in TABLE 1 was melted.

Comparative Example 2

[0069] A comparative aluminum alloy die casting material 2 was obtained in the same manner as in Example 1 except that the aluminum alloy having the composition shown as Comparative Example 2 in TABLE 1 was melted.

[Tensile Test]

[0070] A 14B test piece specified in JIS-Z2241 was collected from the obtained example aluminum alloy die casting materials 1 to 3 and comparative aluminum alloy die casting materials 1 and 2, and when a tensile test was conducted at room temperature, the results of the 0.2% resistance and the elongation at break are as shown in TABLE 2, respectively.

TABLE-US-00002 TABLE 2 0.2% proof stress (MPa) Elongation at break (%) Ex. 1 119 15 Ex. 2 110 16 Ex. 3 112 16 Com. Ex. 1 103 14 Com. Ex. 2 151 8

[0071] All of the example aluminum alloy die casting materials 1 to 3 satisfy 0.2% proof stress of 110 MPa or more and elongation of 10% or more. On the other hand, in the comparative aluminum alloy die casting material 1, since Cr is not added in an appropriate amount, the 0.2% proof stress remains at 103 MPa. Further, in the comparative aluminum alloy die casting material 2, high proof stress is obtained by adding Mg, but a decrease in ductility due to the Mg—Si compound is observed, and the elongation is 8%.

[Structural Observation]

[0072] The cross sections of the example aluminum alloy die casting materials 1 to 3 and the comparative aluminum alloy die casting material 1 were mirror-polished and observed with an optical microscope. The optical micrograph of the example aluminum alloy die casting material 1 is shown in FIG. 1, the optical micrograph of the example aluminum alloy die casting material 2 is shown in FIG. 2, the optical micrograph of the example aluminum alloy die casting material 3 is shown in FIG. 3, and the comparative aluminum alloy die casting material 1 is shown in FIG. 4, respectively.

[0073] When the field of 100 μm×100 μm selected from the optical micrographs of the example aluminum alloy die casting material 3 was targeted for image analysis, and the average value of the equivalent circle diameter of the eutectic Si structure and the cross-sectional area ratio of the Cr-based crystallized product to the whole were measured, the average value of the equivalent circle diameter of the eutectic Si structure was 2 μm, and the cross-sectional area ratio of the Cr-based crystallized product to the whole was 7%.