Steel material for dissimilar metal joining, joined body of dissimilar metals and process for joining dissimilar metal materials

• US 8,337,998 B2
• Filed: 01/26/2012
• Issued: 12/25/2012
• Est. Priority Date: 06/13/2008
• Status: Active Grant

• Current Assignee: Kobe Steel Limited
• Original Assignee: Kobe Steel Limited
• Inventors: Takeda, Mikako, Nagao, Mamoru, Kinefuchi, Masao
• Primary Examiner(s): Zimmerman, John J
• Application Number:
  US13/358,705
• Publication Number:
  US 20120121931A1
• Time in Patent Office: 334 Days
• Field of Search: None
• US Class Current: 428/653
• CPC Class Codes: B23K 11/20 of different metals
• CPC Class Codes: B23K 20/1265 Non-butt welded joints, e.g. overlap-joints, T-joints or spot welds
• CPC Class Codes: B23K 20/2275 the other layer being aluminium
• CPC Class Codes: B23K 2101/006 Vehicles
• CPC Class Codes: B23K 2103/04 Steel or steel alloys
• CPC Class Codes: B23K 2103/20 Ferrous alloys and aluminium or alloys thereof
• CPC Class Codes: B23K 31/025 Connecting cutting edges or the like to tools; Attaching reinforcements to workpieces, e.g. wear-resisting zones to tableware
• CPC Class Codes: B23K 35/002 at least one of the workpieces being of light metal
• CPC Class Codes: B23K 35/004 at least one of the workpieces being of a metal of the iron group
• CPC Class Codes: B23K 9/007 Spot arc welding
• CPC Class Codes: B23K 9/23 taking account of the properties of the materials to be welded
• CPC Class Codes: C21D 1/76 Adjusting the composition of the atmosphere
• CPC Class Codes: C22C 21/02 with silicon as the next major constituent
• CPC Class Codes: C22C 21/06 with magnesium as the next major constituent
• CPC Class Codes: C22C 38/001 containing N
• CPC Class Codes: C22C 38/02 containing silicon
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: Y10T 428/12347 Plural layers discontinuously bonded [e.g., spot-weld, mechanical fastener, etc.]
• CPC Class Codes: Y10T 428/12458 having composition, density, or hardness gradient
• CPC Class Codes: Y10T 428/1259 Oxide
• CPC Class Codes: Y10T 428/12757 : Fe

Abstract

A joined body of dissimilar metals which is produced by joining a steel material and an aluminum alloy material, wherein the steel material to be joined has a specific composition and is specified in the compositions of outer surface oxide layer and inner oxide layer and the aluminum alloy material to be joined is an Al—Mg-base or Al—Zn—Mg-base aluminum alloy having a specific composition. In the joined body of dissimilar metals, a content of Fe at a joint interface on the aluminum alloy material side is regulated, and a reaction layer of Fe and Al is formed at the joint interface of the joined body of dissimilar metals. The joined body of dissimilar metals exhibits high joint strength.

Claims

1. A joined body of dissimilar metals, produced by joining a steel material and an aluminum alloy material, wherein the steel material comprises Fe and:

C;

0.01 to 0.30 mass %;

Si;

0.1 to 3.00 mass %;

Mn;

0.1 to 3.00 mass %;

P;

0 to 0.10 mass %;

S;

0 to 0.05 mass %; and

N;

0 to 300 ppm, and

a ratio occupied by an outer oxide comprising Mn and Si at a total amount of 1 at % or more, which is present on the steel material surface, is 80 to 100% as an average ratio of a total length of the oxide occupied for a length of 1 μ

m in a substantially horizontal direction of an interface between a steel body and an outer oxide layer,

wherein the aluminum alloy material is a 7000 series aluminum alloy comprising Al and 1.0 mass % or more of Mg, and

wherein the joined body comprises a reaction layer comprising Fe and Al at a joint interface between the steel material and the aluminum alloy material, and a content of Fe at a joint interface on an aluminum alloy material side is 2.0% by mass or less.

2. The joined body of claim 1, joined by spot-welding, wherein, in every spot welding place, an average thickness in a nugget depth direction of the reaction layer is in a range of 0.1 to 3 μ

m, and a formation area of the reaction layer is 70% or more of a spot welding area.

3. The joined body of claim 1, having a peeling strength of 2 kN or more, measured by a cross tensile test piece.

4. The joined body of claim 1, in the form of a vehicle body structure of an automobile.

5. The joined body of claim 1, wherein the ratio occupied by the outer oxide comprising Mn and Si at a total amount of 1 at % or more is 90 to 100%.

6. The joined body of claim 1, wherein the 7000 series aluminum alloy material further comprises:

Zn;

4.5 to 6.5 mass %; and

Fe;

0.01 to 0.40 mass %,

wherein a content of the Mg in the aluminum alloy is in a range from 1.0 to 2.0 mass %.

7. The joined body of claim 6, wherein the 7000 series aluminum alloy material further comprises at least one selected from the group consisting of:

Mn;

0.01 to 0.6 mass %;

Cr;

0.01 to 0.2 mass %;

Zr;

0.01 to 0.25 mass %; and

Ti;

0.001 to 0.10 mass %.

8. The joined body of claim 7, wherein a total content of the Mn, Cr, Zr, and Ti contained in the 7000 series aluminum alloy material is 0.30 mass % or less.

9. The joined body of claim 6, wherein the 7000 series aluminum alloy material further comprises:

Cu;

0.01 to 0.2 mass %.

10. The joined body of claim 6, wherein the ratio occupied by the outer oxide comprising Mn and Si at a total amount of 1 at % or more is 90 to 100%.

11. The joined body of claim 6, having a peeling strength of 2 kN or more, measured by a cross tensile test piece.

12. A process for joining dissimilar metal materials, the process comprising:

spot-welding or spot friction stir-welding a steel material and an aluminum alloy material,

wherein the steel material comprises Fe and;

C;

0.01 to 0.30 mass %;

Si;

0.1 to 3.00 mass %;

Mn;

0.1 to 3.00 mass %;

P;

0 to 0.10 mass %;

S;

0 to 0.05 mass %; and

N;

0 to 300 ppm, and

a ratio occupied by an outer oxide comprising Mn and Si at a total amount of 1 at % or more, which is present on the steel material surface, is 80 to 100% as an average ratio of a total length of the oxide occupied for a length of 1 μ

m in a substantially horizontal direction of an interface between a steel body and an outer oxide layer, and

wherein the aluminum alloy material is a 7000 series aluminum alloy comprising Al and 1.0 mass % or more of Mg.

13. The process of claim 12, wherein the spot welding comprises applying an interelectrode current of 10 to 35 kA at an interelectrode pressure of 2.0 to 3.0 kN for a time of 200×

tmsec or shorter at every spot welding place, wherein t is a thickness, in mm, of an aluminum alloy material part to be welded.