Casting aluminum alloy and casting produced using the same

Abstract

An AlMgSi-based aluminum alloy includes 0.015 to 0.12 mass % of Sr, the aluminum alloy producing a cast metal structure in which Mg.sub.2Si is crystallized in a fine agglomerate form.

Claims

1. An aluminum alloy that is an AlMgSi-based aluminum alloy consisting of 2.0 to 7.5 mass % of Mg, 2.0 to 3.5 mass % of Si, and 0.015 to 0.12 mass % of Sr, with the balance being aluminum and unavoidable impurities.

2. A casting produced using the aluminum alloy as defined in claim 1, wherein Mg.sub.2Si is crystallized in a fine agglomerate form.

3. The aluminum alloy as defined in claim 1, comprising 3.0 to 7.0 mass % of Mg.

4. An aluminum alloy that is an AlMgSi-based aluminum alloy consisting of 2.0 to 7.5 mass % of Mg, 2.0 to 3.5 mass % of Si, 0.0015 to 0.12 mass % of Sr, and 0.40 mass % or less of Fe, with the balance being aluminum and unavoidable impurities.

5. A casting produced using the aluminum alloy as defined in claim 4, wherein Mg.sub.2Si is crystallized in a fine agglomerate form.

6. The aluminum alloy as defined in claim 4, comprising 3.0 to 7.0 mass % of Mg.

7. An aluminum alloy that is an AlMgSi-based aluminum alloy consisting of 2.0 to 7.5 mass % of Mg, 2.0 to 3.5 mass % of Si, 0.015 to 0.12 mass % of Sr, 0.3 to 1.0 mass % of Mn, and 0.40 mass % or less of Fe, with the balance being aluminum and unavoidable impurities.

8. A casting produced using the aluminum alloy as defined in claim 7, wherein Mg.sub.2Si is crystallized in a fine agglomerate form.

9. The aluminum alloy as defined in claim 7, comprising 3.0 to 7.0 mass % of Mg.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates the chemical composition of each alloy used for experimental evaluation, and the evaluation results for each alloy.

(2) FIG. 2 is a schematic view illustrating an I-beam mold used when evaluating casting crack resistance.

(3) FIG. 3A illustrates a casting crack fracture surface, and FIG. 3B illustrates a hot tearing fracture surface.

(4) FIG. 4 illustrates a photograph of a microstructure when each component was added to an Al6% Mg3% Si composition.

(5) FIG. 5A illustrates an SEM area analysis photograph when Sr was added to an Al6% Mg3% Si composition, and FIG. 5B illustrates an SEM area analysis photograph when Sr was not added to an Al6% Mg3% Si composition.

(6) FIG. 6A illustrates an etching analysis photograph when Sr was added to an Al6% Mg3% Si composition, and FIG. 6B illustrates an etching analysis photograph when Sr was not added to an Al6% Mg3% Si composition.

DESCRIPTION OF EMBODIMENTS

(7) The castability of the AlMgSi-based alloy according to the invention was evaluated by preparing each molten metal having the chemical composition listed in FIG. 1 (table), and casting each molten metal using an I-beam mold.

(8) FIG. 2 is a schematic view illustrating the I-beam mold used for casting.

(9) In order to determine the difference in shrinkage stress due to the restraint length, three types of molds in which the depth C of the cavity was 25 mm, and the longitudinal length was 70, 95, or 140 mm, were used.

(10) A thermal insulation material A was bonded to the center of the mold in the longitudinal direction so that shrinkage stress is concentrated on the final solidification part, and cracks occur at an identical position.

(11) Bubbling with argon gas was performed for about 120 seconds in order to reduce the hydrogen content in the molten metal.

(12) The mold temperature was set to 4735 K when pouring the molten metal, and the molten metal was cast at a temperature higher than the melting point of each composition by 505 K.

(13) The fracture surface of the resulting I-beam casting (sample) in which cracks or complete fracture was observed in the final solidification part was observed using an SEM. A casting crack fracture surface having dendrite cells (see FIG. 3A), and a hot tearing fracture surface with a trace of plastic deformation (see FIG. 3B), were observed from the secondary electron image.

(14) The casting crack fracture surface (see FIG. 3A) was divided into 15 areas. An 11-step value (0 to 10) was assigned to each area, a case where the casting crack ratio was 100% being assigned a value of 10, and the casting crack area ratio was calculated (i.e., the total value of the entire fracture surface was divided by the maximum value (=150)).

(15) The results are listed in FIG. 1 (table).

(16) The evaluation results for the alloys of Examples 1 to 7 (inventive alloys) and the alloys of Comparative Examples 11 to 15 are listed in FIG. 1.

(17) In Examples 1 to 4 and Comparative Examples 14 and 15, the Sr content was changed with respect to the Al6% Mg3% Si composition.

(18) As is clear from a comparison with the alloy of Comparative Example 15 to which Sr was not added, the casting crack resistance was improved due to the addition of Sr.

(19) A significant effect was observed in Example 1 (Sr content=0.018 mass %) (i.e., more than 0.015 mass %), and the casting crack area ratio was 0% in Example 2 in which the Sr content was 0.03 mass %. The casting crack area ratio was 0% when the Sr content was 0.06 mass % or less (see Example 4).

(20) In Example 5 in which the Sr content was 0.12 mass %, the casting crack resistance decreased to some extent.

(21) AlSiSr-based crystallized products (compounds) were observed when the fracture surface of the alloy of Example 5 was observed using an SEM.

(22) In the castings of Examples 2 to 4, almost all (100%) of the Mg.sub.2Si crystallized phase had a fine agglomerate form.

(23) In Example 6 in which 0.6 mass % of Mn was added in addition to 0.04 mass % of Sr, and Example 7 in which Ti and B were added in addition to 0.04 mass % of Sr, the effect of the addition of Sr was also observed.

(24) In Comparative Examples 11 to 13 in which the AlMgSi-based alloy composition was used, the effect of the addition of Ti and B was observed, but the casting crack area ratio did not reach 0%.

(25) A change in metal structure due to the addition of Sr was also determined. FIG. 4 illustrates a photograph of the microstructure of a casting obtained when each component was added to an Al6% Mg3% composition, and FIGS. 5A and 5B illustrate the SEM area analysis results (mapping analysis results) for each component.

(26) Note that BEI in FIGS. 5A and 5B indicates a backscattered electron image.

(27) As is clear from the photographs illustrated in FIG. 4, the needle-like (elongated) growth of Mg.sub.2Si (length: about 30 m or more) was observed when Sr and/or TiB was not added.

(28) The length of Mg.sub.2Si was reduced to some extent when TiB was added. However, the same refinement effect as that observed due to the addition of Sr was not observed.

(29) As is clear from FIGS. 5A and 5B (mapping analysis results), it was found that the crystallized products were Mg.sub.2Si.

(30) In order to determine the shape of Mg.sub.2Si, the Al6% Mg3% sample to which 0.03 mass % of Sr was added and the Al6% Mg3% sample to which Sr was not added (see FIG. 4) were corroded (only in the aluminum phase) using a sodium hydroxide aqueous solution to expose the Mg.sub.2Si eutectic phase.

(31) FIGS. 6A and 6B illustrate the SEM secondary electron image of each sample.

(32) The sample illustrated in FIG. 6A (to which Sr was not added) had a lamellar crystallization form in which coarse plate-like layers having a thickness of 1 to 2 m and a size of about 30 m or more were stacked.

(33) On the other hand, the sample illustrated in FIG. 6B (to which Sr was added in a ratio of 0.03 mass %) had a crystallization form in which Mg.sub.2Si was crystallized in a fine agglomerate form (thickness: 2 to 3 m, size: 20 m or less, average size: 10 m or less).

(34) The casting aluminum alloy according to the invention exhibits excellent casting crack resistance while maintaining the high ductility and the high strength of an AlMgSi-based aluminum alloy. Therefore, the casting aluminum alloy according to the invention can be widely used to produce a casting (cast product) that is used in the fields of mechanical parts, airplanes, vehicles, and the like for which these properties are required.