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

• US 8,221,899 B2
• Filed: 04/24/2009
• Issued: 07/17/2012
• Est. Priority Date: 06/13/2008
• Status: Active Grant

• Current Assignee: Klaus Schmidt
• Original Assignee: Kobe Steel Limited
• Inventors: Takeda, Mikako, Nagao, Mamoru, Kinefuchi, Masao
• Primary Examiner(s): Zimmerman, John J
• Application Number:
  US12/997,801
• Publication Number:
  US 20110097595A1
• Time in Patent Office: 1,180 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—Si-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 steel material, comprising 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,

wherein a ratio of an oxide present in a grain boundary and an oxide present in grains comprising Mn and Si at a total amount of 1 at % or more, as oxides present in a steel region at a depth from a steel body surface of the steel material to 20 μ

m, is 5% or more and less than 20% as an average area ratio occupied in the steel region,

wherein 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 0.1% or more and less than 50% 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.

2. A joined body of dissimilar metals, produced by joining the steel material of claim 1 and an aluminum alloy material,

wherein the aluminum alloy material is a 6000 series aluminum alloy comprising Al and:

Mg;

0.1 to 3.0 mass %;

Si;

0.1 to 2.5 mass %; and

Cu;

0.001 to 1.0 mass %, 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 the joint interface on an aluminum alloy material side is 2.0% by mass or less.

3. The joined body of claim 2, 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.

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

5. The joined body of claim 2, in the form of a vehicle body structure of an automobile.

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

spot-welding or spot friction stir-welding the steel material of claim 1 and an aluminum alloy material,

wherein the aluminum alloy material is a 6000 series aluminum alloy comprising Al and;

Mg;

0.1 to 3.0 mass %;

Si;

0.1 to 2.5 mass %; and

Cu;

0.001 to 1.0 mass %.

7. The process of claim 6, wherein the spot-welding comprises applying at every joining place between the steel material and the aluminum alloy material, 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, wherein t is a thickness, in mm, of an aluminum alloy material part to be welded.

8. 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%; and

N;

0 to 300 ppm,

wherein the aluminum alloy material is a 6000 series aluminum alloy comprising Al and;

Mg;

0.1 to 3.0 mass %;

Si;

0.1 to 2.5 mass %;

Cu;

0.001 to 1.0 mass %, and

at least one selected from the group consisting of Li;

0.01 to 0.5 mass % and Mn;

0.1 to 0.5 mass %, 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 the joint interface on an aluminum alloy material side is 2.0% by mass or less, and

wherein the joined body has a peeling strength of 2.5 kN or more, measured by a cross tensile test piece.

9. The joined body of claim 8, 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.

10. The joined body of claim 8, wherein an outer oxide layer present on the steel material surface to be joined has a composition in which a ratio occupied by an oxide containing Mn and Si at a total amount of 1 at % or more is 50 to 80%, 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.

11. The joined body of claim 8, wherein a ratio occupied by an oxide present in a grain boundary and an oxide present in grains comprising Mn and Si at a total amount of 1 at % or more, which are present in a steel region at a depth from a steel body surface of the steel material to be welded to 10 μ

m, is 3% or more and less than 10% as an average area ratio occupied in the steel region.

12. The joined body of claim 8, in the form of a vehicle body structure of an automobile.

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

mutually joining, by spot-welding or spot friction stir-welding, a steel material and an aluminum alloy material at a place where a total thickness of the steel material and the aluminum alloy material is 3 mm or less, to obtain a joined body having a peeling strength of 2 kN or more, measured by a cross tensile test piece,

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,

wherein, prior to the joining, the steel material comprises an outer oxide layer present on a steel material surface having a composition in which a ratio occupied by an oxide comprising Mn and Si at a total amount of 1 at % or more is 50 to 80%, 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 6000 series aluminum alloy comprising Al and;

Mg;

0.1 to 3.0 mass %;

Si;

0.1 to 2.5 mass %;

Cu;

0.001 to 1.0 mass %; and

at least one selected from the group consisting of Li;

0.001 to 0.5 mass % and Mn;

0.1 to 0.5 mass %, 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 the joint interface on an aluminum alloy material side of the joined body is 2.0% by mass or less.

14. The process of claim 13, 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.

15. The process of claim 13, 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 joining area.

16. The process of claim 13, wherein, prior to the joining, a ratio occupied by an oxide present in a grain boundary and an oxide in grains comprising Mn and Si at a total amount of 1 at % or more, which are present in a steel region at a depth from a steel body surface of the steel material to be welded to 10 μ

m, is 3% or more and less than 10% as an average area ratio occupied in the steel region.