Electrode for resistance spot welding of dissimilar materials

Patent metadata

Field	Value
Publication number	US-11084119-B2
Application number	US-201815992748-A
Country	US
Kind code	B2
Filing date	May 30, 2018
Priority date	Feb 14, 2014
Publication date	Aug 10, 2021
Grant date	Aug 10, 2021

Abstract

A method of spot welding a workpiece stack-up that includes a steel workpiece and an aluminum alloy workpiece involves passing an electrical current through the workpieces and between welding electrodes that are constructed to affect the current density of the electrical current. The welding electrodes, more specifically, are constructed to render the density of the electrical current greater in the steel workpiece than in the aluminum alloy workpiece. This difference in current densities can be accomplished by passing, at least initially, the electrical current between a weld face of the welding electrode in contact with the steel workpiece and a perimeter region of a weld face of the welding electrode in contact with the aluminum alloy workpiece.

First claim

The invention claimed is:

1. A spot-welded workpiece stack-up comprising:
a steel workpiece that has an indented contact patch on an electrode contacting surface thereof;
an aluminum alloy workpiece that overlaps the steel workpiece to provide a faying interface, the aluminum alloy workpiece having an annular indented contact patch in an electrode contacting surface thereof, the annular indented contact patch extending into the aluminum alloy workpiece and having a bulge located therein; and
a weld joint at the faying interface of the steel and aluminum alloy workpieces between the indented contact patch on the steel workpiece and the annular indented contact patch on the aluminum alloy workpiece, the weld joint metallurgically joining the steel and aluminum alloy workpieces together,
wherein the annular indented contact patch in the electrode contacting surface of the aluminum alloy workpiece surrounds and delimits the bulge located within the aluminum alloy workpiece.

2. The spot-welded workpiece stack-up set forth in claim 1 , wherein the weld joint comprises an aluminum alloy weld nugget and a Fe—Al intermetallic layer between the aluminum alloy weld nugget and the steel workpiece.

3. The spot-welded workpiece stack-up set forth in claim 2 , wherein the Fe—Al intermetallic layer has a thickness of about 1 μm to about 3 μm at least underneath the bulge.

4. The spot-welded workpiece stack-up set forth in claim 2 , wherein the aluminum alloy weld nugget penetrates into the aluminum alloy workpiece from the faying interface of the steel and aluminum alloy workpieces to a distance that ranges from 20% to 100% of a thickness of the aluminum alloy workpiece.

5. The spot-welded workpiece stack-up set forth in claim 1 , wherein the steel workpiece includes a steel weld nugget therein that does not extend to the faying interface.

6. The spot-welded workpiece stack-up set forth in claim 1 , wherein the bulge is smaller in average cross-sectional area than the weld joint.

7. The spot-welded workpiece stack-up set forth in claim 1 , wherein the steel workpiece is a galvanized low carbon steel, a low carbon bare steel, or a galvanized advanced high strength steel, and wherein the aluminum alloy workpiece is an aluminum-magnesium alloy, an aluminum-silicon alloy, an aluminum-magnesium-silicon alloy, or an aluminum-zinc alloy.

8. A spot-welded workpiece stack-up comprising:
a steel workpiece that has an indented contact patch on an electrode contacting surface thereof;
an aluminum alloy workpiece that overlaps the steel workpiece to provide a faying interface, the aluminum alloy workpiece having an indented contact patch in an electrode contacting surface thereof, the indented contact patch extending into the aluminum alloy workpiece and having a bulge therein; and
a weld joint at the faying interface of the steel and aluminum alloy workpieces between the indented contact patch on the steel workpiece and the indented contact patch on the aluminum alloy workpiece, the weld joint metallurgically joining the steel and aluminum alloy workpieces together and comprising an aluminum alloy weld nugget as well as a Fe—Al intermetallic layer situated between the aluminum alloy weld nugget and the steel workpiece, the Fe—Al intermetallic layer having a thickness of about 1 μm to about 3 μm at least underneath the bulge,
wherein the aluminum alloy weld nugget penetrates into the aluminum alloy workpiece from the faying interface of the steel and aluminum alloy workpieces.

9. The spot-welded workpiece stack-up set forth in claim 8 , wherein a steel weld nugget is contained within the steel workpiece but does not extend to either a faying surface of the steel workpiece or the electrode-contacting surface of the steel workpiece.

10. The spot-welded workpiece stack-up set forth in claim 8 , wherein the aluminum alloy weld nugget penetrates into the aluminum alloy workpiece from the faying interface of the steel and aluminum alloy workpieces to a distance that ranges from 20% to 100% of a thickness of the aluminum alloy workpiece.

11. The spot-welded workpiece stack-up set forth in claim 8 , wherein the steel workpiece is a galvanized low carbon steel, a low carbon bare steel, or a galvanized advanced high strength steel, and wherein the aluminum alloy workpiece is an aluminum-magnesium alloy, an aluminum-silicon alloy, an aluminum-magnesium-silicon alloy, or an aluminum-zinc alloy.

12. The spot-welded workpiece stack-up set forth in claim 8 , wherein the bulge is smaller in average cross-sectional area than the weld joint.

13. A welding electrode comprising:
a body that defines an accessible hollow recess for insertion of and attachment with an electrode holder; and
a weld face having a depression located about a central longitudinal axis of the weld face and a perimeter region that surrounds the depression,
wherein a diameter of the weld face ranges from 6 mm to 12 mm,
wherein the perimeter region of the weld face includes an annular perimeter base surface that surrounds and delimits an opening of the depression, and
wherein the annular perimeter base surface provides the weld face with a radius of curvature in a range of from 15 mm to 300 mm.

14. The welding electrode set forth in claim 13 , wherein the depression is defined by a rounded bottom that connects with the annular perimeter base surface and is downwardly displaced from an imaginary plane that spans the opening of the depression.

15. The welding electrode set forth in claim 13 , wherein the annular perimeter base surface has a continuous area of at least 28 mm 2 distributed evenly around the depression.

16. The welding electrode set forth in claim 13 , wherein the depression is defined by a bottom and a continuous peripheral side wall that connects the bottom with the annular perimeter base surface, the bottom being downwardly displaced from an imaginary plane that spans the opening of the depression.

17. The welding electrode set forth in claim 16 , wherein the peripheral side wall is tapered toward the bottom of the depression so that a width of the depression decreases from the opening of the depression to the bottom of the depression, and wherein the peripheral side wall has a draft angle of at least 3°.

18. The welding electrode set forth in claim 13 , wherein the depression has a depth that ranges from 0.1 mm to 3.0 mm and a width that ranges from 2 mm to 10 mm at the opening of the depression.

19. The welding electrode set forth in claim 13 , wherein the weld face further includes a ringed projection that surrounds the central longitudinal axis of the weld face and rises upwardly from a base surface of the weld face to define the depression on its inside.

Assignees

• Gm Global Tech Operations Llc

Inventors

• Yang David
• Sigler David R
• Carlson Blair E
• Schroth James G
• Karagoulis Michael J

Classifications

• B23K11/115 Primary

  by means of two electrodes placed opposite one another on both sides of the welded parts · CPC title

• B23K35/0261

  Rods, electrodes or wires · CPC title

• B23K11/20 Primary

  of different metals · CPC title

• B23K11/3018

  Cooled pressure electrodes · CPC title

• B23K2103/20

  Ferrous alloys and aluminium or alloys thereof · CPC title