Provided is a resistance spot welding method that inhibits, in accordance with the degree of axis misalignment between electrodes, the occurrence of cracking in a weld regardless of the steel grade. In resistance spot welding methods according to the present invention, H (ms) is an electrode force retaining time after completion of current passage, D (mm) is an amount of axis misalignment between the electrodes, t (mm) is a total sum of sheet thicknesses of a plurality of overlapping steel sheets, T (MPa) is a tensile strength of a steel sheet having a highest tensile strength among the plurality of steel sheets, F (N) is an electrode force, and d (mm) is a tip diameter of one electrode of the pair of electrodes that has a smaller tip diameter. The electrode force retaining time H is specified to be a predetermined value or greater.

A method of resistance spot welding a workpiece stack-up comprising overlapping first and second steel workpieces is disclosed, wherein at least one of the steel workpieces comprises an advanced high-strength steel substrate. The workpiece stack-up is positioned between a pair of opposed first and second welding electrodes. A cover is disposed between at least one of the first steel workpiece and the first welding electrode or the second steel workpiece and the second welding electrode at an intended weld site. The workpiece stack-up is clamped between the first and second welding electrodes at the weld site such that at least one of the weld faces of the first and second welding electrodes presses against the cover. The first and second steel workpieces are welded together by passing an electrical current between the first and second welding electrodes at the weld site.

A galvanized steel sheet includes: a steel sheet having a chemical composition satisfying an equivalent carbon content Ceq of 0.35% or more and less than 0.60%, and a specified steel microstructure; and a galvanized layer on a surface of the steel sheet. The retained austenite has a solute C content of 0.6% or more by mass, and retained austenite grains with an aspect ratio of less than 2.0 constitute 50% or more of all retained austenite grains. In 90-degree bending at a curvature radius/thickness ratio of 4.2 in a rolling (L) direction with respect to an axis extending in a width (C) direction, an L cross section in a 0 to 50 ?m region from a surface of the steel sheet on a compression side has a number density of voids of 1000/mm.sup.2 or less, and the galvanized steel sheet has a tensile strength of 590 MPa or more.

The present invention provides a spot welding method for a member to be welded constituted of a plurality of steel sheets that are overlapped with each other at at least a welding zone, in which at least an overlapped face of at least one of the plurality of steel sheets at the welding zone is coated with zinc plating, a total sheet thickness t (mm) of the plurality of steel sheets is 1.35 mm or more, a squeeze time St (seconds) from the time when welding electrodes are brought into contact with the member to be welded to the time when electric current flow for welding starts satisfies 0.020?St, and a hold time Ht( seconds) after welding from the time when electric current flow for welding between the welding electrodes ends to the time when the welding electrodes and the member to be welded are brought out of contact satisfies 0.015t.sup.2+0.020?Ht.

A system and method for bonding structures includes a method of bonding a first panel to a second panel. An adhesive material is applied to at least one of the first panel and the second panel and is disposed between the first panel and the second panel. A welding device having at least a first electrode and a second electrode is configured to receive and position the first panel and second panel between the first and second electrodes. The welding device generates an electric current with the first and second electrodes to apply to the first panel and the second panel. The electric current generates thermal energy having a first temperature that cures the adhesive material positioned between the first and second electrodes to bond the first panel with the second panel.

A steel welded member having a high LME resistance of a spot weld, i.e., a steel welded member comprised of a plurality of Zn-based plated steel materials, each comprised of a steel material and a Zn-based plating layer on its surface, joined by at least one spot weld, in which

at least one of the Zn-based plated steel materials has a 780 MPa or more tensile strength, that steel material has a chemical composition containing, by mass %,

C: 0.05 to 0.40%,

Si: 0.2 to 3.0%,

Mn: 0.1 to 5.0%,

sol. Al: 0.4 to 1.50%, etc. and having a balance of Fe and impurities, and,

in a region of 10 to 300 m from an end of a pressure weld of the spot weld, a difference of a Zn penetration depth of Zn from a Zn-based plating layer penetrating a steel material minus a depth of an internal oxidation layer formed at the steel material is within 0.1 to 10.0 m in range.

A spot welded joint of at least two steel sheets is provided. At least one of the steel sheets presents yield strength above or equal to 600 MPa, an ultimate tensile strength above or equal to 1000 MPa, uniform elongation above or equal to 15%. The base metal chemical composition includes 0.05C0.21%, 4.0Mn7.0%, 0.5Al3.5%, Si2.0%, Ti0.2%, V0.2%, Nb0.2%, P0.025%, B0.0035%, and the spot welded joint contains a molten zone microstructure containing more than 0.5% of Al and containing a surface fraction of segregated areas lower than 1%, said segregated areas being zones larger than 20 m.sup.2 and containing more than the steel nominal phosphorus content.

A spot welding method able to simply prevent liquid metal embrittlement cracks in spot welding of plated steel sheets, comprising, before spot welding, removing the plating at least in a zone including the inside of a circle centered at a scheduled location where the center of the nugget is formed and having an outer circumference of the inside of the outer edge of a weld affected zone or a zone at the mated surfaces of the steel sheets to be welded at the inside of a circle sharing a center of a scheduled location becoming the center of the nugget formed at the mated surfaces of the steel sheets and having an outer circumference of the inside of the outer edge of a weld affected zone

Resistance spot welding is performed on a combination of overlapping steel sheets including at least one steel sheet that has, on a surface thereof, a coated layer with zinc as a main component, by (1) starting electric current passage in a state satisfying 0.9tL1.1t; and (2) dividing electric current into main current and initial current that precedes the main current and is two-step current, setting a current value I.sub.1 during current in a first step of the initial current to satisfy I.sub.m1.1I.sub.115.0 kA with respect to a current value I.sub.m during the main current, and setting a current value I.sub.2 in the subsequent second step to no current or low current satisfying 0I.sub.2I.sub.m0.7.

A method for welding a stack of sheets having a plurality of sheets of different materials is provided. In an aspect, the stack of sheets includes an aluminum sheet and a galvanneal steel sheet. In an aspect, the method includes resistively spot welding the galvanneal sheet to a hot-stamped steel sheet placed between the aluminum sheet and the galvanneal sheet, the sheet of hot-stamped steel including stress relief sections. The method further includes placing a metal foil on the aluminum sheet and vaporizing the metal foil to project portions of the aluminum sheet through the stress relief sections of the hot-stamped steel sheet to weld the portions of the aluminum sheet to the galvanized steel sheet. In another aspect, the method includes placing the metal foil on a raised portion of the aluminum sheet and projecting the raised portion of the aluminum onto the galvanneal steel sheet.