MULTI-STEP DIRECT WELDING OF AN ALUMINUM-BASED WORKPIECE TO A STEEL WORKPIECE

• US 20150053655A1
• Filed: 08/20/2014
• Published: 02/26/2015
• Est. Priority Date: 08/23/2013
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations LLC (General Motors Company)
• Inventors: Sigler, David R., Carlson, Blair E., Karagoulis, Michael J., Myasnikova, Yelena
• Granted Patent: US 9,999,938 B2
• Time in Patent Office: Days
• US Class Current: 219/91.22
• CPC Class Codes: B23K 11/115 by means of two electrodes placed opposite one another on both sides of the welded parts
• CPC Class Codes: B23K 11/20 of different metals
• CPC Class Codes: B23K 2103/20 Ferrous alloys and aluminium or alloys thereof

Abstract

A workpiece stack-up that includes at least a steel workpiece and an aluminum-based workpiece can be resistance spot welded by employing a multi-stage spot welding method in which the passage of electrical current is controlled to perform multiple stages of weld joint development. The multiple stages include: (1) a molten weld pool growth stage in which a molten weld pool is initiated and grown within the aluminum-based workpiece; (2) a molten weld pool solidification stage in which the molten weld pool is allowed to cool and solidify into a weld nugget that forms all or part of a weld joint; (3) a weld nugget re-melting stage in which at least a portion of the weld nugget is re-melted; and (4) a re-melted weld nugget solidification stage in which the re-melted portion of the weld nugget is allowed to cool and solidify.

Claims

1. A method of resistance spot welding a workpiece stack-up, which includes an aluminum-based workpiece and a steel workpiece, so as to form a resistance spot weld joint between the aluminum-based workpiece and the steel workpiece, the method comprising:

contacting a workpiece stack-up with a pair of spot welding electrodes such that the spot welding electrodes make contact with opposed sides of the workpiece stack-up, the workpiece stack-up comprising an aluminum-based workpiece and a steel workpiece, the aluminum-based workpiece having a faying surface and the steel workpiece having a faying surface, and wherein the faying surfaces of the aluminum-based workpiece and the steel workpiece overlap and contact one another to provide a faying interface between the workpieces; and

controlling the passage of electrical current between the spot welding electrodes and through the aluminum-based workpiece and the steel workpiece to perform multiple stages of weld joint development that include;

growing a molten weld pool in the aluminum-based workpiece that extends from the faying interface into the aluminum-based workpiece;

allowing the molten weld pool to cool and solidify into a weld nugget that includes a weld bond area joined to the faying surface of the steel workpiece;

re-melting at least a portion of the weld nugget including at least part of the weld bond area of the weld nugget;

allowing the re-melted portion of the weld nugget to cool and solidify.

2. The method set forth in claim 1, wherein electrical current in the form of current pulses is passed between the spot welding electrodes to re-melt at least a portion of the weld nugget.

3. The method set forth in claim 1, wherein the weld nugget extends into the aluminum-based alloy workpiece from the faying surface to a penetration depth, and wherein the re-melted portion of the weld nugget does not extend to the penetration depth of the weld nugget.

4. The method set forth in claim 1, wherein the re-melted portion of the weld nugget is entirely confined within the weld bond area.

5. The method set forth in claim 1, wherein the re-melted portion of the weld nugget includes up to 100% of the weld bond area of the weld nugget.

6. The method set forth in claim 1, wherein the re-melted portion of the weld nugget includes the entire weld bond area of the weld nugget and further combines with molten material of the aluminum-based alloy workpiece outside of the weld bond area of the weld nugget to establish an enlarged weld bond area.

7. The method set forth in claim 6, wherein the enlarged weld bond area is up to 50% greater in area than the weld bond area of the weld nugget before re-melting.

8. The method set forth in claim 1, wherein the steel workpiece is galvanized steel or bare steel.

9. The method set forth in claim 1, wherein the aluminum-based workpiece comprises an aluminum-magnesium alloy, an aluminum-silicon alloy, an aluminum-magnesium-silicon alloy, or an aluminum-zinc alloy.

10. The method set forth in claim 1, further comprising:

expelling at least part of the re-melted portion of the weld nugget at the faying interface.

11. The method set forth in claim 10, wherein, prior to re-melting at least a portion of the weld nugget, the weld bond area of the weld nugget is at least 4(π

)(t), where t is a thickness of the aluminum-based workpiece at the weld site.

12. A method of resistance spot welding a workpiece stack-up, which includes an aluminum-based workpiece and a steel workpiece, so as to form a resistance spot weld joint between the aluminum-based workpiece and the steel workpiece, the method comprising:

providing a workpiece stack-up that includes an aluminum-based workpiece and a steel workpiece, the aluminum-based workpiece having a faying surface and the steel workpiece having a faying surface, and wherein the faying surfaces of the workpieces overlap and contact one another to provide a faying interface between the workpieces;

passing electrical current through the aluminum-based alloy workpiece and the steel workpiece and across the faying interface for a first period of time during which a molten weld pool that extends from the faying interface into the aluminum-based workpiece is initiated and grown;

allowing the molten weld pool to cool and solidify into a weld nugget by either, for a second period of time after passage of electrical current for the first period of time, passing electrical current through the workpieces at a reduced level that allows for solidification of the molten weld pool or ceasing passage of electrical current through the workpieces; and

passing electrical current through the aluminum-based alloy workpiece and the steel workpiece for a third period of time, after the weld nugget has solidified during the second period of time, during which at least a portion of the weld nugget is re-melted.

13. The method set forth in claim 12, wherein the weld nugget extends into the aluminum-based workpiece to a penetration depth, and wherein re-melted portion of the weld nugget does not extend to the penetration depth of the weld nugget.

14. The method set forth in claim 12, wherein the weld nugget includes a weld bond area joined to a faying surface of the steel workpiece at the faying interface, and wherein the re-melted portion of the weld nugget includes the entire weld bond area of the weld nugget and further combines with molten material of the aluminum-based alloy workpiece outside of the weld bond area of the weld nugget, and wherein, upon cooling and solidification, the re-melted portion of the weld nugget and the molten material of the aluminum-based alloy workpiece outside of the weld bond area of the weld nugget establish an enlarged weld bond area.

15. The method set forth in claim 12, further comprising:

expelling at least part of the re-melted portion of the weld nugget at the faying interface.

16. The method set forth in claim 15, wherein expelling at least part of the re-melted portion of the weld nugget is caused by passing electrical current through the aluminum-based alloy workpiece and the steel workpiece for a fourth period of time, after the third period of time, during which electrical current is raised to a higher level than in the third period of time.

17. The method set forth in claim 12, wherein the steel workpiece is galvanized steel or bare steel, and wherein the aluminum-based workpiece comprises an aluminum-magnesium alloy, an aluminum-silicon alloy, an aluminum-magnesium-silicon alloy, or an aluminum-zinc alloy.

18. A multi-stage spot welding method comprising:

pressing a pair of spot welding electrodes against a workpiece stack-up such that the spot welding electrodes are pressed against opposed sides of the workpiece stack-up, the workpiece stack-up comprising an aluminum-based workpiece and a steel workpiece;

growing a molten weld pool in the aluminum-based workpiece that extends from a faying interface of the steel workpiece and the aluminum-based workpiece into the aluminum-based workpiece;

allowing the molten weld pool to solidify into a weld nugget that includes a weld bond area joined to a faying surface of the steel workpiece at the faying interface;

re-melting at least a portion of the weld nugget that includes at least part of the weld bond area; and

allowing the re-melted portion of the weld nugget to solidify into a re-solidified portion of the weld nugget.

19. The method set forth in claim 18, further comprising:

expelling at least part of the re-melted portion of the weld nugget at the faying interface before allowing the re-melted portion of the weld nugget to solidify.

20. The method set forth in claim 18, wherein, prior to re-melting at least a portion of the weld nugget, the weld bond area of the weld nugget is at least 4(π

)(t), where t is a thickness of the aluminum-based workpiece at the weld site.