Abstract: A spot welding method includes a heating step of energizing an electrode in pressure contact with an Al alloy member to heat and melt a join part by resistance heating and a cooling step of cooling the join part after the heating step in a state in which the electrode is in pressure contact with the Al alloy member. The alloy is a wrought alloy of Mg: 0.2 to 1.2 mass %, Si: 0.4 to 1.5%, and Cu: 1.1% or less or a casting alloy of Si: 7 to 11% and Mg: 0.1 to 0.4% with respect to 100% as a whole. The cooling step includes a first cooling process performed with a reduced amount of input energy to the join part as compared with the heating step and a second cooling process performed after the first cooling process at a higher cooling rate than that in the first cooling process.

Abstract: Resistance spot welding includes a first process of performing energization by pressurizing two or more metal plates superposed by sandwiching a pair of electrode tips, and a second process of stopping energization in the first process and pressurizing two or more metal plates by a pair of electrode tips. The estimation method for the nugget diameter includes: a thickness estimation process of estimating the nugget thickness using the amount of expansion in the thickness direction of two or more metal plates in the first process and the electric resistance value between the pair of electrode tips in the first process; and a diameter estimation process of estimating the nugget diameter using the expansion amount and the electric resistance value when the nugget is estimated to have reached the interface between two adjacent metal plates using the respective thicknesses of the two or more metal plates and the estimated nugget thickness.

Abstract: A spot welding method including: a main energization step of energizing a pair of opposing electrodes in pressure contact with both outer surfaces of a set of sheets where multiple sheet materials are stacked, thereby to cause melting between facing surfaces of the sheet materials; and a pressing variation step of, prior to the main energization step, causing a pulsation of pressing force applied to the set of sheets from the electrodes. A resin material such as an adhesive or a sealant may be interposed between the facing surfaces of at least a pair of the sheet materials. The period of the pulsation is 0.01 to 0.7 seconds. The amplitude of the pulsation is 10% to 90% with respect to a reference value of the pressing force. The set of sheets may include a first and a second steel sheet, and an aluminum alloy sheet that are stacked in order.

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.

Abstract: A method of manufacturing a member for fastening by joining a nut with a tubular joint portion extending from a main body formed with an internal thread to a panel with a mounting hole for the nut on an aluminum base material. The joint portion has a rotation-preventing portion with a concave and convex shaped outer peripheral surface and a guide portion extending from the rotation-preventing portion to one side. After the guide portion is inserted into the mounting hole, the nut is energized by electrodes in contact with both nut end surface sides. The nut then generates heat, and the periphery of the mounting hole is heated and softened. When the nut is pressurized with the electrodes, the rotation-preventing portion bites into the mounting hole, and the one end portion of the guide portion is swaged to become a retaining portion on one surface side of the panel.

Abstract: A metal joined body has an iron base body and an aluminum base body that are joined together via a joint layer. The joint layer has a first layer composed of a first intermetallic compound formed on the iron base body side and a second layer composed of a second intermetallic compound formed on the aluminum base body side. The first layer has one or more first protrusions that merge integrally into the iron base body and extend in a pile shape into the first intermetallic compound. The second layer may have one or more second protrusions that are composed of a second intermetallic compound and extend in a columnar shape into the aluminum base body. The first intermetallic compound may contain Al5Fe2, and the second intermetallic compound may contain Al3Fe. The total thickness of the first layer and the second layer is, for example, 2 to 15 ?m.

Abstract: A resistance spot welding method includes the steps of: removing at least part of oil on a surface of a welding target material by energization between a pair of electrodes; and after the oil removal step, forming a nugget in an overlapped portion of the welding target material by energization between the pair of electrodes.

Abstract: A welding determination method is provided, which determines whether a spot welding part is joined to an electrode without using resistance generated when separating the electrode from a workpiece. In the method, the workpiece made by laminating multiple metal sheets is clamped under pressure by a pair of electrodes and melted by a current applied, and after that the conduction is stopped to hold the workpiece in a pressurized state to determine whether the joining occurs. The method includes the steps of: deriving resistance between the pair of electrodes and pressurizing force by the pair of electrodes during conduction to the workpiece; and determining whether the spot welding part is joined to the electrodes based on a first index value calculated using the derived resistance and resistance in an ideal welding, and on a second index value calculated using the derived pressurizing force and pressurizing force in the ideal welding.

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.

Abstract: A spot welding method includes a heating step of energizing an electrode in pressure contact with an Al alloy member to heat and melt a join part by resistance heating and a cooling step of cooling the join part after the heating step in a state in which the electrode is in pressure contact with the Al alloy member. The alloy is a wrought alloy of Mg: 0.2 to 1.2 mass %, Si: 0.4 to 1.5%, and Cu: 1.1% or less or a casting alloy of Si: 7 to 11% and Mg: 0.1 to 0.4% with respect to 100% as a whole. The cooling step includes a first cooling process performed with a reduced amount of input energy to the join part as compared with the heating step and a second cooling process performed after the first cooling process at a higher cooling rate than that in the first cooling process.