A steel plate frame and a thin plate are made of different materials. A plurality of through holes are formed in a portion of the thin plate to be placed on the steel plate frame. A plurality of projections 6c are formed on a support plate, each of the projections being allowed to be inserted into a corresponding one of the through holes. An adhesive is applied to a portion of the steel plate frame on which the thin plate is placed. The thin plate is placed on the steel plate frame, and the steel plate frame and the thin plate are bonded together by the adhesive. The support plate is placed on the thin plate to insert the projections into the through holes. The projections and the steel plate frame are welded to form a plurality of welded spots.

A weld joint is disclosed that weld bonds together an aluminum workpiece and a steel workpiece. The weld joint includes an aluminum weld nugget, an intermetallic layer, and an annular ring of aluminide particles that is selected from the group consisting of nickel aluminide particles, iron aluminide particles, and a combination thereof. The annular ring of aluminide particles extends upwards from a weld bond surface of the weld joint such that the annular ring of aluminide particles extends radially inwardly into the aluminum weld nugget and protects the weld bond surface of the weld joint against crack propagation that may originate from a notch root of the weld joint.

A weld joint is disclosed that weld bonds together an aluminum workpiece and a steel workpiece. The weld joint includes an aluminum weld nugget, an intermetallic layer, and an annular ring of aluminide particles that is selected from the group consisting of nickel aluminide particles, iron aluminide particles, and a combination thereof. The annular ring of aluminide particles extends upwards from a weld bond surface of the weld joint such that the annular ring of aluminide particles extends radially inwardly into the aluminum weld nugget and protects the weld bond surface of the weld joint against crack propagation that may originate from a notch root of the weld joint.

A welding electrode is disclosed that includes an electrode welding shell and a blind adapter that are joined together to cooperatively define an internal cavity. The electrode welding shell and the blind adapter may be integrally formed or they may be distinct components that are attached together. The presence of the internal cavity defined by the electrode welding shell and the blind adapter reduces the thermal mass of the welding electrode and slows the rate of conductive heat transfer from the weld face to a cooling fluid, which allows in the center of the weld face to retain heat for a longer duration once current flow through the welding electrode is terminated, thereby positively affecting the spot welding process for particular types of workpiece stack-ups including those that include an aluminum workpiece and an overlapping adjacent steel workpiece.

A welding electrode is disclosed that includes an electrode welding shell and a blind adapter that are joined together to cooperatively define an internal cavity. The electrode welding shell and the blind adapter may be integrally formed or they may be distinct components that are attached together. The presence of the internal cavity defined by the electrode welding shell and the blind adapter reduces the thermal mass of the welding electrode and slows the rate of conductive heat transfer from the weld face to a cooling fluid, which allows in the center of the weld face to retain heat for a longer duration once current flow through the welding electrode is terminated, thereby positively affecting the spot welding process for particular types of workpiece stack-ups including those that include an aluminum workpiece and an overlapping adjacent steel workpiece.

A method of resistance spot welding an aluminum workpiece and an adjacent overlapping steel workpiece is disclosed in which a source of a reactive metal in a diffusible state is located along a faying interface of an aluminum workpiece and an adjacent overlapping steel workpiece. The source of the reactive metal in a diffusible state may take on a variety of forms including (1) a composite adhesive layer that includes reactive particles dispersed throughout a structural thermosetting adhesive matrix or (1) a reactive alloy layer that confronts and is in proximate contact with a faying surface of the aluminum workpiece. Once the source of a reactive material in a diffusible state is in place and the workpiece stack-up is assembled, an electrical current is passed through the workpiece stack-up and between a set of opposed welding electrodes at a weld zone to ultimately produce a weld joint.

A method of resistance spot welding an aluminum workpiece and an adjacent overlapping steel workpiece is disclosed in which a source of a reactive metal in a diffusible state is located along a faying interface of an aluminum workpiece and an adjacent overlapping steel workpiece. The source of the reactive metal in a diffusible state may take on a variety of forms including (1) a composite adhesive layer that includes reactive particles dispersed throughout a structural thermosetting adhesive matrix or (1) a reactive alloy layer that confronts and is in proximate contact with a faying surface of the aluminum workpiece. Once the source of a reactive material in a diffusible state is in place and the workpiece stack-up is assembled, an electrical current is passed through the workpiece stack-up and between a set of opposed welding electrodes at a weld zone to ultimately produce a weld joint.

A radially slotted welding electrode is disclosed that may be used in conjunction with a companion second welding electrode to conduct resistance spot welding on a workpiece stack-up assembly that includes a steel workpiece and an overlapping adjacent aluminum workpiece, especially when an intermediate organic material layer is disposed between the workpiece faying surfaces of the steel and aluminum workpieces. The radially slotted welding electrode includes a weld face that has a central upstanding plateau and a convex dome portion that surrounds the central upstanding plateau and which includes a plurality of circumferentially spaced trapezoidal weld face sections that include transverse upstanding arcuate ridges. Together, the central upstanding plateau and the trapezoidal weld face sections of the convex dome portion define an annular channel that surrounds the central plateau and a plurality of radial slots that communicate with and extend outwards from the central channel.

A radially slotted welding electrode is disclosed that may be used in conjunction with a companion second welding electrode to conduct resistance spot welding on a workpiece stack-up assembly that includes a steel workpiece and an overlapping adjacent aluminum workpiece, especially when an intermediate organic material layer is disposed between the workpiece faying surfaces of the steel and aluminum workpieces. The radially slotted welding electrode includes a weld face that has a central upstanding plateau and a convex dome portion that surrounds the central upstanding plateau and which includes a plurality of circumferentially spaced trapezoidal weld face sections that include transverse upstanding arcuate ridges. Together, the central upstanding plateau and the trapezoidal weld face sections of the convex dome portion define an annular channel that surrounds the central plateau and a plurality of radial slots that communicate with and extend outwards from the central channel.

A mounting unit includes a mounting part for a mating surface of a basic structure which cannot be welded to the mounting part and a welding element fixed in a through-bore of the mounting part. The welding element corresponds to the bore and has a thickness at least as large as the mounting part. An annular groove is formed in the welding element. A part of the welding element bounding the groove on the outside forms a form-locking connection element expanded outward and fixing the welding element in the bore by a form-locking connection toward the mounting side. A central region radially within the annular groove is a welding surface for the mating surface, is aligned with or protrudes beyond a mounting-side edge region of the bore with an overhang and is aligned with or projects over the form-locking connection element. A production method is also provided.