Aluminum alloy and die casting method

Abstract

A method for casting an aluminum alloy includes: pouring molten metal of an aluminum alloy comprising 6.0 to 9.0 mass % of Si, 0.4 to 0.8 mass % of Mg, 0.25 to 1.0 mass % of Cu, 0.08 to 0.25 mass % of Fe, 0.6 mass % or less of Mn, 0.2 mass % or less of Ti, and 0.01 mass % or less of Sr, with the balance being Al and unavoidable impurities into a shot sleeve of a die casting machine; filling a mold cavity of a center-gate die with the molten metal at a gate speed of 1 msec or less so as to produce a laminar flow, and subjecting T5 heat treatment so as to obtain the aluminum alloy having a tensile strength of 240 MPa or more.

Claims

1. A method for casting an aluminum alloy comprising: directly pouring molten metal of an aluminum alloy comprising 6.0 to 9.0 mass % of Si, 0.4 to 0.8 mass % of Mg, 0.25 to 1.0 mass % of Cu, 0.08 to 0.25 mass % of Fe, 0.6 mass % or less of Mn, 0.2 mass % or less of Ti, and 0.01 mass % or less of Sr, with the balance being Al and unavoidable impurities into a shot sleeve of a die casting machine; filling a mold cavity of a center-gate die with the molten metal at a gate speed of 1 m/sec or less so as to produce a laminar flow, and performing T5 heat treatment at 180 degrees C. for 180 minutes so as to obtain the aluminum alloy having a tensile strength of 240 MPa or more.

2. The method as defined in claim 1, wherein a powdery release agent is applied to the inside of the mold cavity.

3. The method as defined in claim 1, wherein the molten metal of aluminum alloy comprising 0.006 to 0.01 mass % of Sr.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIGS. 1A and 1B illustrate the chemical components of aluminum alloys subjected to evaluation, and the evaluation results.

(2) FIGS. 2A and 2B illustrate a photograph of the structure of the aluminum alloy obtained in Example 1.

(3) FIG. 3A illustrates a photograph of the structure of the aluminum alloy obtained in Comparative Example 1, FIG. 3B illustrates a photograph of the structure of the aluminum alloy obtained in Comparative Example 6, and FIG. 3C illustrates a photograph of the structure of the aluminum alloy obtained in Comparative Example 10.

(4) FIGS. 4A to 4D illustrate an example of the shape of a cast product. FIG. 5 schematically illustrates the principle of a die casting process.

(5) FIG. 6 illustrates an example of a die structure in which an intermediate die is provided between a stationary die and a movable die.

DESCRIPTION OF EMBODIMENTS

(6) The aluminum alloy and the casting method according to the invention are further described below.

(7) Molten metal of each aluminum alloy including the chemical components listed in FIG. 1A (having the composition listed in FIG. 1A) was prepared, and subjected to a die casting process to produce a product. It may be possible to add one element among Sb, Ca, and Na in ratio of 0.01 mass % or less instead of Sr in FIG. 1A, since Sb, Ca, or Na has the same effect as Sr.

(8) A JIS No. 14 proportional test piece was cut from the product, and the mechanical properties were evaluated using the test piece.

(9) The die casting process was performed at a gate speed as low as 1 msec or less so as to produce a laminar flow.

(10) A heat treatment (T5) was then performed at 180° C. for 180 minutes.

(11) FIG. 6 illustrates an example of the die structure.

(12) The evaluation results are listed in FIG. 1B (table).

(13) In FIG. 1B, the target values are specified for the mechanical properties (tensile strength, yield strength (0.2%), and elongation).

(14) In Examples 1 to 12, the content of each chemical component was set to be within the specific target range, and good mechanical properties were obtained.

(15) Since good mechanical properties were obtained by the T5 heat treatment, it is possible to reduce cost.

(16) In Comparative Examples 1 to 3, the elongation was lower than the target value since a modification was not applied.

(17) In Comparative Example 2, good strength was obtained by a T6 treatment, but the elongation was lower than the target value, and an increase in cost occurs due to the T6 treatment.

(18) In Comparative Example 4, good mechanical properties were obtained. However, since a T6 treatment was applied, an increase in cost occurs.

(19) In Comparative Example 5, good mechanical properties were not obtained by a T5 treatment since the Cu content was low.

(20) In Comparative Example 6, the elongation was lower than the target value since a modification was not applied, and the Cu content and the Si content were outside the specific ranges.

(21) Since the Mn content was high in Comparative Example 6, coarse crystallized products were formed, and the elongation was lower than the target value.

(22) Since a T6 treatment is required in Comparative Example 6, an increase in cost occurs.

(23) In Comparative Example 7, the elongation was lower than the target value since a modification was not applied, and the Cu content and the Si content were outside the specific ranges.

(24) Since the Mn content was high in Comparative Example 7, coarse crystallized products were observed, and the elongation was lower than the target value.

(25) In Comparative Example 8, since the Cu content was outside the specific range, and the Mn content was high, coarse crystallized products were observed, and the elongation was lower than the target value.

(26) In Comparative Example 9, good mechanical properties were not obtained since the Cu content was low.

(27) In Comparative Example 10, a T6 treatment was applied (i.e., an increase in cost occurs).

(28) In Comparative Example 11, good mechanical properties were not obtained since the Mg content was low.

(29) In Comparative Example 12, a T6 treatment was applied (i.e., an increase in cost occurs).

(30) FIGS. 2A and 2B illustrate a photograph of the metal structure obtained in Example 1, FIG. 3A illustrates a photograph of the metal structure obtained in Comparative Example 1, FIG. 3B illustrates a photograph of the metal structure obtained in Comparative Example 6 and FIG. 3C illustrates a photograph of the metal structure obtained in Comparative Example 10.

(31) It was confirmed that eutectic silicon was refined when the aluminum alloy according to the invention was used.

(32) The die structure is described below.

(33) As illustrated in FIG. 5 (schematic view), a cavity 13 is formed by a stationary die 11 and a movable die 12. When implementing the die casting process, molten metal is poured into a sleeve 14, and injected into the cavity 13.

(34) Die casting machines are classified into a horizontal die casting machine and a vertical die casting machine. A horizontal die casting machine is mainly used at present from the viewpoint of productivity and the like.

(35) Horizontal die casting machines are classified into an under-gate die casting machine (in which the gate is provided on the lower side) (see FIG. 5) and a center-gate die casting machine (in which the gate is provided at the center).

(36) For example, when producing a cylindrical product and the like illustrated in FIGS. 4A to 4D (cross-sectional views), it is possible to suppress the occurrence of segregation and obtain excellent internal quality by injecting the molten metal into the cavity at a position corresponding to the center of the product (see the die structure illustrated in FIG. 6).

(37) Therefore, it is preferable to use a center-gate die, and fill the cavity with the molten metal at a gate speed (i.e., the speed at which the molten metal passes through the runner gate of the die) of 1 msec or less so as to produce a laminar flow.

(38) Note that a center-gate die casting machine in which the gate is provided at the center may also be used (not illustrated in the drawings). When a die structure is formed so that an intermediate die 15 is provided between the stationary die 11 and the movable die 12 (see FIG. 6), it is possible to form a center-gate die having a center gate 11a using an under-gate die casting machine (in which the gate is provided on the lower side) by providing a runner between the stationary die 11 and the intermediate die 15.

(39) It is possible to produce products having various shapes (see FIGS. 4A to 4D) by utilizing such a die structure that includes three split dies.

INDUSTRIAL APPLICABILITY

(40) The aluminum alloy according to the invention exhibits high strength without the need for a T6 treatment and can be applied to various automotive parts and various mechanical parts. The aluminum alloy according to the invention exhibits excellent die castability, and achieves high productivity.