The present disclose provides a method of resistance spot welding that can inhibit Liquid Metal Embrittlement-induced cracking in zinc-coated steel plates irrespective of the plate thicknesses. One aspect of the present disclosure provides a method of resistance spot welding that includes welding a workpiece with a resistance spot welding apparatus. The workpiece includes two or more steel plates in an overlapping state. The two or more steel plates include at least one steel plate coated with zinc. The welding includes causing a cooling rate of a high-tensile steel plate among the two or more steel plates to be higher than a cooling rate of an other steel plate among the two or more steel plates. The high-tensile steel plate has a tensile strength higher than a tensile strength of the other steel plate.

A system for spot welding two metal sheets together includes a plurality of conductive particles placed in an interface between the two metal sheets, a first electrode, and a second electrode. The first electrode and the second electrode are arranged to clamp the two metal sheets together such that the conductive particles become embedded into the metal sheets at the interface between the metal sheets. A conductive path is formed from the first electrode to the second electrode through the metal sheets and the plurality of metallic particles.

A resistance spot welding method can be used to join polymeric and metallic workpieces together and includes the following steps: (a) placing an electrically conductive coating between a polymeric workpiece and a metallic workpiece, wherein the metallic workpiece has a textured surface facing the polymeric workpiece; (b) piercing the polymeric workpiece with first and second electrically conductive pins of a welding electrode assembly; (c) applying electrical energy to the first and second electrically conductive pins so that an electrical current flows through the first electrically conductive pin, the electrically conductive coating, and the second electrically conductive pin in order to at least partially melt the polymeric workpiece and the electrically conductive coating, thereby forming a weld pool; and (d) cooling the weld pool to form a solid weld nugget in order to establish a mechanical interface lock between the solid weld nugget and the textured surface.

A method for producing a zinc or zinc-alloy coated steel sheet with a tensile strength higher than 900 MPa, for the fabrication of resistance spot welds containing in average not more than two Liquid Metal Embrittlement cracks per weld having a depth of 100 ?m or more, with steps of providing a cold-rolled steel sheet, heating cold-rolled steel sheet up to a temperature T1 between 550? C. and Ac1+50? C. in a furnace zone with an atmosphere (A1) containing from 2 to 15% hydrogen by volume, so that the iron is not oxidized, then adding in the furnace atmosphere, water steam or oxygen with an injection flow rate Q higher than (0.07%/h??), ? being equal to 1 if said element is water steam or equal to 0.52 if said element is oxygen, at a temperature T?T1, so to obtain an atmosphere (A2) with a dew point DP2 between ?15? C. and the temperature Te of the iron/iron oxide equilibrium dew point, then heating the sheet from temperature T.sub.1 up to a temperature T.sub.2 between 720? C. and 1000? C. in a furnace zone under an atmosphere (A2) of nitrogen containing from 2 to 15% hydrogen and more than 0.1% CO by volume, with an oxygen partial pressure higher than 10.sup.?21 atm., wherein the duration to of heating of the sheet from temperature T.sub.1 up to the end of soaking at temperature T.sub.2 is between 100 and 500 s, soaking the sheet at T.sub.2, then cooling the sheet at a rate between 10 and 400? C./s, then coating the sheet with zinc or zinc-alloy coating.

The resistance welding method of welding two objects together includes the steps of: clamping the objects between a pair of electrodes; and applying a current between the electrodes while the objects are pressed to bring them close to each other to allow a contacting surface between them to generate heat. One object includes a core member and a plated layer coating the core member and having a melting point lower than that of a metal constituting an outer surface of the core member. The objects are clamped between the electrodes and the contacting surface are allowed to generate heat to melt the plated layer to weld the outer surface of the core member of the one object and a base member of another object together. At least the outer surface of the core member and the base member are made of respective metals, between which no intermetallic compound is formed.

A welding method for the manufacture of an assembly of at least two steel substrates spot welded together through at least one spot welded joint, including A. provision of substrates including a press hardened steel part obtained by press hardening of a steel sheet coated with an aluminium based coating, B. application of a spot-welding cycle with welding electrodes and a spot-welding power source applying a current, the cycle including: at least three pulsations, each having the same maximum pulsation current (Cp) applied through the substrates, each pulsation duration p being identical and set from 20 to 60 ms, each pulsation being followed by the same cooling time c set from 30 to 50 ms, wherein the welding parameter Wp value is at least 0.8, Wp being defined as Wp=(t?c)/p t being the average thickness of the substrate in mm, c being the cooling time in ms, p being the pulsation duration in ms.

A joint structure, includes: a first member including a high tensile strength steel; a second member including a high tensile strength steel and superposed on the first member; a surface soft layer formed on at least one of a superposition surface of the first member, on which the second member is superposed, and a superposition surface of the second member, on which the first member is superposed; a molten-solidified portion formed by melting and solidifying the first member and the second member; and a heat affected zone formed around the molten-solidified portion, in which the surface soft layer has a total thickness of 5 ?m to 200 ?m, and the molten-solidified portion has a carbon amount of 0.21 mass % or more, and a maximum Vickers hardness of the surface soft layer in the heat affected zone is 100 Hv to 500 Hv.

A resistance spot welding method inhibits, in accordance with the electrode angle, the occurrence of cracking in the weld regardless of the steel grade. The resistance spot welding method satisfies relationships:

2.Math.A.Math.(t.Math.T/F).sup.1/2H when 0A<1

(3.Math.A1).Math.(t.Math.T/F).sup.1/2H when 1A<10

(A+19).Math.(t.Math.T/F).sup.1/2H when 10A<20

where H (ms) is an electrode force retaining time after completion of current passage, A (degrees) is an electrode angle of the electrodes, t (mm) is a sheet thickness of a steel sheet having a largest sheet thickness among the steel sheets, T (MPa) is a tensile strength of a steel sheet having a highest tensile strength among the two or more steel sheets, and F (N) is the electrode force.

A method of projection welding hardware to a plated steel sheet for hot stamping, may include pressing hardware and a plated steel sheet in a state in which a welding projection on the hardware is in contact with the plated steel sheet, supplying a primary current to the hardware and the plated steel sheet in a state in which they are pressed, and supplying a secondary current to the hardware and the plated steel sheet.

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.