Spot welding method

Patent metadata

Field	Value
Publication number	US-11772186-B2
Application number	US-202117373123-A
Country	US
Kind code	B2
Filing date	Jul 12, 2021
Priority date	Oct 9, 2020
Publication date	Oct 3, 2023
Grant date	Oct 3, 2023

Abstract

A novel spot welding method for steel sheets and an aluminum alloy sheet, includes stacked sheet materials from a pair of opposing electrodes to join the sheet materials by resistance heating. The pair of opposing electrodes are in pressure contact with both outer surfaces of the sheet sets. The sheet sets include at least a first and second steel sheet, and an aluminum alloy sheet stacked in this order. A first energization step forms a molten pool between facing surfaces of the first and second steel sheets without melting the aluminum alloy sheet. A second energization step causes a melting reaction between facing surfaces of the second steel sheet and the aluminum alloy sheet. The first and second steel sheets are joined via a first nugget. The second steel sheet and the aluminum alloy sheet are joined via a second nugget including an intermetallic compound generated by the melting reaction.

First claim

The invention claimed is:

1. A spot welding method of energizing a set of sheets comprising a plurality of stacked sheet materials from a pair of opposing electrodes to join the sheet materials by resistance heating, the pair of opposing electrodes being in pressure contact with both outer surfaces of the set of sheets,
the set of sheets comprising at least a first steel sheet, a second steel sheet, and an aluminum alloy sheet that are stacked in this order,
the spot welding method comprising:
a first energization step of forming a molten pool between facing surfaces of the first steel sheet and the second steel sheet without melting the aluminum alloy sheet; and
a second energization step of, after the first energization step, causing a melting reaction between facing surfaces of the second steel sheet and the aluminum alloy sheet,

the first steel sheet and the second steel sheet being joined via a first nugget,
the second steel sheet and the aluminum alloy sheet being joined via a second nugget including an intermetallic compound generated by the melting reaction,
wherein an energization time of the first energization step is shorter than an energization time of the second energization step.

2. The spot welding method according to claim 1 , wherein the second energization step is performed by energization with a current value smaller than a melting current value that allows the aluminum alloy sheet to be melted only by the resistance heating.

3. The spot welding method according to claim 1 , wherein
the first energization step and the second energization step are performed by energization with a DC current,
the first energization step includes energization with a first current value of 4 to 10 kA, and
the second energization step includes energization with a second current value of 10 to 15 kA.

4. The spot welding method according to claim 1 , wherein the second energization step is performed with a second current density of 50 to 300 A/mm 2 , wherein the second current density is obtained through dividing a current value by a tip area of the electrode in contact with the aluminum alloy sheet.

5. The spot welding method according to claim 1 , further comprising
a cooling step of, after the first energization step and before the second energization step, lowering a temperature of the set of sheets in contact with the electrodes through no energization or energization with a current value smaller than that during the first energization step.

6. The spot welding method according to claim 1 , further comprising
a heat treatment step of annealing or tempering the set of sheets joined after the second energization step.

7. The spot welding method according to claim 1 , wherein the second steel sheet has a metal layer at least on the aluminum alloy sheet side, wherein the metal layer has a melting point lower than that of the aluminum alloy sheet.

8. The spot welding method according to claim 7 , wherein the metal layer is composed of a galvanized layer.

9. The spot welding method according to claim 1 , wherein
(i) the first energization step is performed by energization with a DC current of 4 to 10 kA for 25 to 150 ms; and
(ii) the second energization step is performed by energization with a DC current of 10 to 15 kA for 150 to 500 ms.

Assignees

• Toyota Chuo Kenkyusho Kk
• Toyota Motor Co Ltd

Inventors

• Matsuoka Hideaki
• Asada Takashi
• Amago Tatsuyuki
• Izuno Kyosuke
• Nakada Koki
• Sekiguchi Tomohiko
• Ogura Shuhei

Classifications

• B23K15/008 Primary

  Spot welding · CPC title

• B23K11/115

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

• B23K35/0238

  layered · CPC title

• B23K35/286

  Al as the principal constituent · CPC title

• B23K35/3053 Primary

  Fe as the principal constituent · CPC title