High-Strength Aluminum Alloy Extruded Material That Exhibits Excellent Formability And Method For Producing The Same

Abstract

An aluminum alloy is provided that is used to produce a high-strength aluminum alloy extruded material that exhibits excellent formability. The aluminum alloy consists of 0.30 to 1.00 mass % of Mg, 0.6 to 1.40 mass % of Si, 0.10 to 0.40 mass % of Fe, 0.10 to 0.40 mass % of Cu, 0.005 to 0.1 mass % of Ti, 0.3 mass % or less of Mn, 0.01 to 2.0 mass % of Zn, and 0.10 mass % or less of Zr, with the balance being aluminum and unavoidable impurities, the aluminum alloy having a stoichiometric Mg.sub.2Si content of 0.60 to 1.30 mass % and an excess Si content of 0.30 to 1.00 mass %.

Claims

1. An aluminum alloy that is used to produce a high-strength aluminum alloy extruded material that exhibits excellent formability, the aluminum alloy consisting of 0.30 to 1.00 mass % of Mg, 0.6 to 1.40 mass % of Si, 0.10 to 0.40 mass % of Fe, 0.10 to 0.40 mass % of Cu, 0.005 to 0.1 mass % of Ti, 0.3 mass % or less of Mn, 0.01 to 2.0 mass % of Zn, and 0.10 mass % or less of Zr, with the balance being aluminum and unavoidable impurities, the aluminum alloy having a stoichiometric Mg.sub.2Si content of 0.60 to 1.30 mass % and an excess Si content of 0.30 to 1.00 mass %.

2. A high-strength aluminum alloy extruded material that exhibits excellent formability, the extruded material being produced using the aluminum alloy as defined in claim 1, the extruded material having a structure in which crystal grains having an aspect ratio of 4.0 or more have an average grain size of 100 m or less.

3. A method for producing a high-strength aluminum alloy extruded material that exhibits excellent formability, the method comprising extruding a billet of the aluminum alloy as defined in claim 1 to obtain an extruded product, air-cooling the extruded product immediately after the extrusion at an average cooling rate of 50 to 150 C./min, and subjecting the cooled extruded product to artificial aging.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0042] FIG. 1 illustrates the composition of each aluminum alloy used for evaluation.

[0043] FIG. 2 illustrates the billet casting conditions and the subsequent production conditions.

[0044] FIG. 3 illustrates the evaluation results for each extruded material.

DESCRIPTION OF EMBODIMENTS

[0045] Molten metal of each aluminum alloy having the composition listed in FIG. 1 (table) was prepared, and cast to obtain a columnar billet.

[0046] The casting speed is listed in FIG. 2 (table).

[0047] The billet was homogenized under the HOMO conditions listed in FIG. 2 (table).

[0048] Note that the material of Comparative Example 15 is a rolled material.

[0049] The billet was preheated to the BLT temperature listed in FIG. 2 (table), extruded at the extrusion speed listed in FIG. 2 (table), and air-cooled (subjected to press quenching) at the cooling rate listed in FIG. 2 (table) immediately after extrusion.

[0050] The air-cooled product was subjected to artificial aging under the heat treatment conditions listed in FIG. 2 (table).

[0051] The evaluation results for the extruded materials thus obtained are listed in FIG. 3 (table).

[0052] The extruded materials subjected to the evaluation were sheet materials having a thickness of 2.0 mm.

[0053] Each item was evaluated as described below.

Tensile Properties

[0054] A JIS No. 4 tensile specimen was prepared from the extruded material in accordance with JIS Z 2241. The specimen was subjected to a tensile test using a tensile tester conforming to the JIS standard.

Impact Resistance

[0055] A JIS V-notch No. 4 specimen was prepared from the extruded material in accordance with JIS Z 2242. The specimen was subjected to a Charpy impact test using a Charpy impact tester conforming to the JIS standard.

[0056] An extruded material having a thickness sufficient to prepare JIS V-notch No. 4 specimen was used.

Crystal Grain Size

[0057] A test material was mirror-polished and etched (3% NaOH, 40 C.3 min). The metal structure of the test material was then observed using an optical microscope at a magnification of 100.

[0058] The aspect ratio (L1/L2) of the test material was measured. Note that the test material has the recrystallized structure that extends in the extrusion axis direction. L1 is the length of the crystal grain of the recrystallized structure in the extrusion direction while L2 is the length of the crystal grain in the thickness direction. Erichsen value

[0059] A sheet material (90 mm90 mm2 (thickness) mm) was prepared from the extruded material in accordance with JIS Z 2247. The specimen was subjected to an Erichsen test prior to artificial aging.

[0060] Specifically, a steel ball having a diameter of 20 mm was pressed into the surface of the sheet material, and the punch stroke was taken as the Erichsen value when a crack reached to the back side of the sheet material.

[0061] The larger the Erichsen value, the better the formability.

n-Value (Work Hardening Index)

[0062] The term n-value used herein refers to an exponent n when a true stress-true strain curve determined by a load-elongation curve is approximately represented by =F.sup.n.

[0063] The n-value corresponds to the slope of the line in which the true stress-true strain value is plotted into a double logarithmic graph.

[0064] Note that a JIS No. 4 tensile specimen was prepared from the extruded material in accordance with JIS Z 2241, and subjected to a tensile test using a tensile tester conforming to the JIS standard when measuring the n-value.

r-Value (Lankford Value)

[0065] The r-value (Lankford value) is the ratio of the true strain in the widthwise direction to the true strain in the thickness direction of the specimen during the tensile test (see below).

r=(ln w0/w1)/(ln t0/t1)

[0066] Note that w0 and w1 are the width of the specimen before and after the test, and t0 and t1 are the thickness of the specimen before and after the test.

[0067] Note that a JIS No. 4 tensile specimen was prepared from the extruded material in accordance with JIS Z 2241, and subjected to a tensile test using a tensile tester conforming to the JIS standard when measuring the r-value.

[0068] In Examples 1 to 5, the T1 tensile strength was 200 MPa or more, the T1 yield strength was 80 MPa or more, the T5 tensile strength was 245 MPa or more, the T5 yield strength was 205 MPa or more, and the Erichsen value was 11.0 or more (i.e., high strength and excellent formability were obtained) (see FIG. 3 (table)).

[0069] The n-value was 0.30 or more, and the r-value was 0.40 or more.

[0070] The elongation of the T1 material was 24% or more, and the elongation of the T5 material was 8% or more.

[0071] A Charpy impact value of 20 J/cm.sup.2 or more was obtained while achieving high strength.

[0072] In Examples 1 to 5, the microstructure was a flat recrystallized structure, the aspect ratio was 4.0 or more, and the average crystal grain size was 100 m or less.

[0073] In Comparative Example 11, since the Si content was 0.57 mass %, and the excess Si content (exSi) was 0.29 mass % (i.e., 0.30 mass %), the Erichsen value before the T5 treatment was small, and the T5 tensile strength was 200 MPa (i.e., 245 MPa).

[0074] In Comparative Examples 12 to 14, the excess Si content was lower than that of Comparative Example 1, and the Erichsen value was small although the strength was equal to or higher than the target value. Comparative Example 15 is a rolled material that differs from extruded material of Examples 1 to 5. In Comparative Example 15, the T5 yield strength was 122 MPa that was extremely lower than the target value of 205 MPa.

INDUSTRIAL APPLICABILITY

[0075] Since the extruded material produced using the aluminum alloy according to the invention exhibits excellent formability and the like, the extruded material may be used to produce various pressed products, bent products, and the like.