Electrode for resistance spot welding of dissimilar metals

Patent metadata

Field	Value
Publication number	US-10010966-B2
Application number	US-201414181020-A
Country	US
Kind code	B2
Filing date	Feb 14, 2014
Priority date	Feb 14, 2014
Publication date	Jul 3, 2018
Grant date	Jul 3, 2018

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 method of spot welding a workpiece stack-up that includes a steel workpiece and an aluminum alloy workpiece, the method comprising:
providing a stack-up that includes a steel workpiece and an aluminum alloy workpiece that overlap to provide a faying interface;
contacting a weld face of a steel welding electrode with a surface of the steel workpiece;
contacting a weld face of an aluminum alloy welding electrode with a surface of the aluminum alloy workpiece, the weld face of the aluminum alloy welding electrode comprising a depression and a perimeter region surrounding the depression, the perimeter region providing the weld face of the aluminum alloy welding electrode with a radius of curvature of 15 mm to 300 mm; and
passing an electrical current between the steel welding electrode and the aluminum alloy welding electrode to initiate and grow a molten aluminum alloy weld pool within the aluminum alloy workpiece that wets the steel workpiece at the faying interface, the electrical current at least initially passing through the perimeter region of the aluminum alloy welding electrode such that a sectional area through which the electrical current passes expands radially from the faying interface of the steel and aluminum alloy workpieces to the aluminum alloy welding electrode.

2. The method set forth in claim 1 , wherein the perimeter region of the weld face of the aluminum alloy welding electrode comprises an annular perimeter base surface that surrounds and delimits the depression.

3. The method set forth in claim 2 , wherein the depression is defined by a bottom and a tapered peripheral side wall that connects the bottom with the annular perimeter base surface at an opening of the depression.

4. The method set forth in claim 2 , wherein the depression is defined by a concave bottom that connects with the annular perimeter base surface at an opening of the depression.

5. The method set forth in claim 2 , wherein the depression is located about a central axis of the weld face of the aluminum alloy welding electrode.

6. The method set forth in claim 1 , wherein the perimeter region of the weld face of the aluminum alloy welding electrode comprises a ringed projection that rises upwardly from a base surface of the weld face to define the depression on its inside.

7. The method set forth in claim 6 , wherein the ringed projection has a planar surface that is elevated above the base surface.

8. The method set forth in claim 6 , wherein the depression is located about a central axis of the weld face of the aluminum alloy welding electrode.

9. The method set forth in claim 1 , wherein passing the electrical current between the steel welding electrode and the aluminum alloy welding electrode causes the aluminum alloy workpiece to at least partially fill the depression as the weld face of the aluminum alloy welding electrode impresses into the surface of the aluminum alloy workpiece.

10. The method set forth in claim 1 , further comprising:
stopping the electrical current such that the molten aluminum alloy weld pool solidifies into a weld joint at the faying interface of the steel and aluminum alloy workpieces.

11. The method set forth in claim 10 , 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.

12. The method set forth in claim 1 , wherein passing the electrical current between the steel welding electrode and the aluminum alloy welding electrode additionally initiates and grows a molten steel weld pool within the steel workpiece, and wherein stopping the electrical current further solidifies the molten steel weld pool into a steel weld nugget.

13. A method of spot welding a workpiece stack-up that includes a steel workpiece and an aluminum alloy workpiece, the method comprising:
contacting a surface of a steel workpiece with a weld face of a steel welding electrode;
contacting a surface of an aluminum alloy workpiece, which overlaps the steel workpiece, with a weld face of an aluminum alloy welding electrode, the weld face of the aluminum alloy welding electrode comprising a depression and a perimeter region surrounding the depression, the perimeter region providing the weld face of the aluminum alloy welding electrode with a radius of curvature of 15 mm to 300 mm;
passing an electrical current between the steel welding electrode and the aluminum alloy welding electrode and across a faying interface of the steel workpiece and the aluminum alloy workpiece to initiate and grow a molten aluminum alloy weld pool within the aluminum alloy workpiece that wets the steel workpiece at the faying interface, wherein the perimeter region of the weld face of the aluminum alloy welding electrode has a continuous contact area with the aluminum alloy workpiece of at least 28 mm 2 distributed evenly around the depression at the onset of current flow between the steel welding electrode and the aluminum alloy welding electrode; and
impressing the aluminum alloy welding electrode into the surface of the aluminum alloy workpiece during passage of the electrical current to form a contact patch that, following cessation of the electrical current, contains a bulge therein.

14. The method set forth in claim 13 , wherein passing the electrical current comprises decreasing a current density of the electrical current within the aluminum alloy workpiece by passing the electrical current through the perimeter region of the weld face of the aluminum alloy welding electrode so that a sectional area through which the electrical current passes expands radially from the faying interface of the workpieces to the aluminum alloy welding electrode.

15. The method set forth in claim 13 , wherein passing the electrical current between the steel welding electrode and the aluminum alloy welding electrode additionally initiates and grows a molten steel weld pool within the steel workpiece.

Assignees

• Gm Global Tech Operations Llc

Inventors

• Yang David S
• 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

• B23K35/0205

  Non-consumable electrodes; C-electrodes · CPC title

• B23K11/3018

  Cooled pressure electrodes · CPC title

• B23K2203/20

  Operations & Transport · mapped topic

• B23K11/20 Primary

  of different metals · CPC title