Aluminum-coated structural member and production method

• US 6,815,087 B2
• Filed: 06/24/2003
• Issued: 11/09/2004
• Est. Priority Date: 07/11/2002
• Status: Active Grant

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Yoshida, Tomoyuki, Takagi, Kiyoshi, Nakanishi, Eizaburo
• Primary Examiner(s): Koehler, Robert R.
• Application Number:
  US10/601,585
• Publication Number:
  US 20040009366A1
• Time in Patent Office: 504 Days
• Field of Search: 428/653, 428/610, 428/640, 428/686, 428/939, 148/516, 148/531, 148/534
• US Class Current: 428/653
• CPC Class Codes: B32B 15/012 one layer being formed of an iron alloy or steel, another layer being formed of aluminium or an aluminium alloy
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C23C 2/12 Aluminium or alloys based thereon
• CPC Class Codes: C23C 2/28 Thermal after-treatment, e.g. treatment in oil bath
• CPC Class Codes: C23C 2/29 Cooling or quenching
• CPC Class Codes: Y10S 428/939 Molten or fused coating
• CPC Class Codes: Y10T 428/12458 having composition, density, or hardness gradient
• CPC Class Codes: Y10T 428/12667 Oxide of transition metal or Al
• CPC Class Codes: Y10T 428/12757 Fe
• CPC Class Codes: Y10T 428/12986 Adjacent functionally defined components

Abstract

An aluminum-coated structural member includes an Al—Si—Fe alloy layer formed on a steel substrate layer. The alloy layer includes a softer region having a hardness smaller than or equal to a hardness of the steel substrate layer, extends from the surface of the steel substrate layer toward a surface of the alloy layer, over a depth range greater than or equal to 50% of a thickness of the alloy layer. The Al—Si—Fe alloy layer has an oxide weight smaller than or equal to 500 mg/dm².

Claims

1. An aluminum-coated structural member comprising:

a steel substrate layer; and

an Al—

Si—

Fe alloy layer formed on a surface of the steel substrate layer, the alloy layer including a softer region having a hardness smaller than or equal to a hardness of the steel substrate layer, extending from the surface of the steel substrate layer toward a surface of the alloy layer, and having a thickness greater than or equal to 50% of a thickness of the alloy layer, the Al—

Si—

Fe alloy layer having an oxide weight smaller than or equal to 500 mg/dm².

2. The aluminum-coated structural member as claimed in claim 1, wherein the Al—

Si—

Fe alloy layer has a multi-layer structure including an inner layer contiguous with the steel substrate layer, and an outer layer forming the surface of the alloy layer.

3. The aluminum-coated structural member as claimed in claim 2, wherein the inner layer is a softest layer in the multi-layer structure.

4. The aluminum-coated structural member as claimed in claim 2, wherein the inner layer contains 85˜

95% Fe, and the inner layer is softer in Hv hardness than an average hardness of the alloy layer by a percentage more than or equal to 20%.

5. The aluminum-coated structural member as claimed in claim 2, wherein the multi-layer structure of the Al—

Si—

Fe alloy layer further comprises an intermediate layer containing 25˜

40% Al, and the intermediate layer is lower in hardness than the steel substrate layer.

6. The aluminum-coated structural member as claimed in claim 2, wherein the multi-layer structure of the Al—

Si—

Fe alloy layer further comprises a plurality of intermediate layers, at least one of the intermediate layers containing 25˜

40% Al, and being lower in hardness than the steel substrate layer.

7. The aluminum-coated structural member as claimed in claim 2, wherein the outer layer of the Al—

Si—

Fe alloy layer is harder than the steel substrate layer.

8. The aluminum-coated structural member as claimed in claim 2, wherein the outer layer contains 35˜

50% Fe.

9. An aluminum-coated structural member comprising:

a steel substrate layer; and

an Al—

Si—

Fe alloy layer formed on a surface of the steel substrate layer, the Al—

Si—

Fe alloy layer having a multi-layer structure including an inner layer contiguous with the steel substrate layer, an outer layer forming a surface of the alloy layer and an intermediate layer formed between the inner and outer layers, the inner layer containing 85˜

95% Fe, the intermediate layer containing 25˜

40% Al, and the outer layer being harder than the steel substrate layer.

10. A production method of an aluminum-coated structural member comprising:

heating a hot-dip aluminum-coated steel sheet at a heating rate in a range of 1˜

10°

C./sec;

holding the hot-dip aluminum steel sheet at a raised temperature in a temperature range of 900˜

950°

C. for a duration in a range of 2˜

8 minutes;

cooling the hot-dip aluminum-coated steel sheet to a temperature in a temperature range of 700˜

800°

C. at a cooling rate in a range of 5˜

15°

C./sec;

forming the hot-dip aluminum-coated steel sheet into a predetermined shape in the temperature range of 700˜

800°

C.; and

cooling the hot-dip aluminum-coated steel sheet in the predetermined shape rapidly from the temperature range of 700˜

800°

C. to a lower temperature lower than or equal to 300°

C. at a cooling rate in a range of 20˜

100°

C./sec.