Multi-stage resistance spot welding method for workpiece stack-up having adjacent steel and aluminum workpieces

Patent metadata

Field	Value
Publication number	US-10245675-B2
Application number	US-201514883249-A
Country	US
Kind code	B2
Filing date	Oct 14, 2015
Priority date	Oct 14, 2015
Publication date	Apr 2, 2019
Grant date	Apr 2, 2019

Abstract

A workpiece stack-up that includes at least a steel workpiece and an adjacent and overlapping aluminum workpiece can be resistance spot welded by a multi-stage spot welding method. The multi-stage spot welding method involves initially forming a weld joint between the steel and aluminum workpieces. The weld joint extends into the aluminum workpiece from the faying interface of the two workpieces and includes an interfacial weld bond area adjacent to and joined with the faying surface of the steel workpiece. After the weld joint is initially formed, the multi-stage spot welding method calls for remelting and resolidifying at least a portion of the weld joint that includes some or all of the interfacial weld bond area. At least a portion of the resultant refined weld joint may then be subjected to the same remelting and resolidifying practice, if desired. Multiple additional practices of remelting and resolidifying may be carried out.

First claim

The invention claimed is:

1. A method of resistance spot welding a workpiece stack-up that includes a steel workpiece and an aluminum workpiece, the method comprising:
(a) providing a workpiece stack-up that has a first side and a second side, the workpiece stack-up comprising a steel workpiece disposed adjacent to and overlapping an aluminum workpiece, the steel workpiece having a faying surface that contacts a faying surface of the aluminum workpiece to establish a faying interface between the workpieces;
(b) passing an electrical current across the faying interface to cause melting of the aluminum workpiece and the formation of a molten aluminum weld pool within the aluminum workpiece that wets the faying surface of the steel workpiece;
(c) allowing the molten aluminum weld pool to solidify into a weld joint that bonds the steel and aluminum workpieces together at the faying interface, the weld joint having an interfacial weld bond area joined with the faying surface of the steel workpiece;
(d) passing an electrical current through the weld joint to remelt at least a portion of the weld joint at the interfacial weld bond area to form a remelted portion of the weld joint;
(e) allowing the remelted portion of the weld joint to resolidify to form a first refined weld joint; and
(f) repeating steps (d) and (e) at least once to produce a final refined weld joint that bonds the steel and aluminum workpieces together at the faying interface.

2. The method set forth in claim 1 , wherein the steel workpiece includes an exterior outer surface that provides the first side of the workpiece stack-up and the aluminum workpiece includes an exterior outer surface that provides the second side of the workpiece stack-up.

3. The method set forth in claim 1 , wherein the workpiece stack-up further comprises an additional aluminum workpiece disposed adjacent to the aluminum workpiece or an additional steel workpiece disposed adjacent to the steel workpiece.

4. The method set forth in claim 1 , wherein the aluminum workpiece comprises a base aluminum substrate comprised of elemental aluminum, an aluminum-magnesium alloy, an aluminum-silicon alloy, an aluminum-magnesium-silicon alloy, or an aluminum-zinc alloy.

5. The method set forth in claim 1 , wherein step (b) comprises passing a direct electrical current across the faying interface, the direct electrical current having a current level that falls between 12 kA and 30 kA and is passed for a period of time that ranges from 50 ms and 500 ms.

6. The method set forth in claim 5 , wherein step (c) comprises ceasing current flow across the faying interface for a time period of 20 ms to 500 ms after passage of the direct electrical current in step (b).

7. The method set forth in claim 6 , wherein step (d) comprises passing a direct electrical current through the weld joint, the direct electrical current having a current level that falls between 15 kA and 30 kA and is passed for a period of time that ranges from 30 ms and 300 ms, and wherein step (e) comprises ceasing current flow for a time period of 20 ms to 500 ms after passage of the direct electrical current in step (d).

8. The method set forth in claim 1 , wherein step (f) includes repeating steps (d) and (e) and additional one to fourteen times.

9. The method set forth in claim 1 , wherein the workpiece stack-up further comprises an intermediate organic material layer between the faying surface of the steel workpiece and the faying surface of the aluminum workpiece at the faying interface.

10. The method set forth in claim 1 , wherein the final refined weld joint includes an interfacial weld bond area bonded to the faying surface of the steel workpiece, and wherein the interfacial weld bond area of the final refined weld joint is greater in surface area than the interfacial weld bond area of the weld joint formed in steps (b) and (c).

11. The method set forth in claim 1 , wherein the remelted portion of the weld joint consumes at least 50% of the interfacial weld bond area of the weld joint.

12. A method of resistance spot welding a workpiece stack-up that includes a steel workpiece and an aluminum workpiece, the method comprising:
providing a workpiece stack-up that has a first side and a second side, the workpiece stack-up comprising a steel workpiece disposed adjacent to and overlapping an aluminum workpiece, the steel workpiece having a faying surface that contacts a faying surface of the aluminum workpiece to establish a faying interface between the workpieces;
bringing a weld face of a first welding electrode and a weld face of a second welding electrode into pressed contact with the first side and the second side of the workpiece stack-up, respectively, the weld face of the first welding electrode and the weld face of the second welding electrode being facially aligned with one another at a weld site when brought into pressed contact with their respective sides of the workpiece stack-up;
resistance spot welding the steel workpiece and the aluminum workpiece together at their faying interface by heating and cooling the weld site in multiple successive stages, each of the multiple successive stages of heating and cooling the weld site comprising passing an electrical current between the first and second welding electrodes and through the weld site at a current level within a working current level range of 10 kA to 40 kA for a duration of 10 ms to 1000 ms to generate heat within the weld site, followed by reducing the current level of the electrical current to within a reduced current level range of 0 kA to 5 kA for a duration of 10 ms to 1000 ms to allow the weld site to cool, and wherein the multiple successive stages of heating and cooling the weld site includes at least:
a weld joint origination stage in which a weld joint is initially formed that joins the steel and aluminum workpieces together at the faying interface, the weld joint extending into the aluminum workpiece and having an interfacial weld bond area adjacent to and joined with a faying surface of the steel workpiece at the faying interface;
a first weld joint refining stage in which at least a portion of the weld joint formed in the weld joint origination stage is remelted and resolidified into a first refined weld joint, wherein remelting of at least a portion of the weld joint produces a remelted portion of the weld joint that encompasses at least 50% of the interfacial weld bond area of the weld joint;
a second weld joint refining stage in which at least a portion of the first refined weld joint formed in the first weld joint refining stage is remelted and resolidified into a second refined weld joint, wherein remelting of at least a portion of the first refined weld joint produces a remelted portion of the first refined weld joint that encompasses at least 50% of an interfacial weld bond area of the first refined weld joint; and

removing the first welding electrode and the second welding electrode from pressed contact with the first side and the second side of the workpiece stack-up, respectively, after resistance spot welding of the steel and aluminum workpieces.

13. The method set forth in claim 12 , wherein the workpiece stack-up further comprises an intermediate organic material layer between the faying surface of the steel workpiece and the faying surface of the aluminum workpiece at the faying interface, the intermediate organic material layer having a thickness between the faying surfaces of the steel and aluminum workpieces that ranges from 0.1 mm to 2.0 mm.

14. The method set forth in claim 13 , wherein the intermediate organic material layer is an uncured, heat-curable adh

Assignees

• Gm Global Tech Operations Llc

Inventors

• Sigler David R
• Carlson Blair E
• Karagoulis Michael J

Classifications

• B23K11/20 Primary

  of different metals · CPC title

• B23K11/185

  of aluminium or aluminium alloys · CPC title

• B23K2103/20

  Ferrous alloys and aluminium or alloys thereof · CPC title

• B23K11/24

  Electric supply or control circuits therefor · CPC title

• B23K11/115

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