Abstract: Provided is a method of resistance spot welding of welding a sheet set including a high strength steel sheet with which a high joint strength can be achieved even for a high Ceq material. A method of resistance spot welding a sheet set of two or more lapped steel sheets by weld the sheet set while clamping and pressing the sheet set between a pair of welding electrodes includes a first welding step of applying an weld current Im (kA) and forming a nugget having a nugget diameter d (mm) that satisfies the following inequality (1); a cooling step, subsequent to the foregoing first welding, of cooling the sheet set while continuing to press the sheet set; and a second welding step of performing two-step welding, 3×?tm?d?6×?tm??(1), where tm is the thickness (mm) of the thinnest one of the foregoing two or more steel sheets.

Abstract: In a welded joint manufactured by a method of resistance spot welding thin steel sheets, when the diameter of a nugget formed from the thin steel sheets is denoted by d, on a horizontal plane passing through a nugget surrounded by a corona bond, distribution of an amount of P in a region in the nugget surrounded by a closed curve at a distance d/100 from an end portion of a weld zone toward the inside of the nugget and a closed curve at a distance d/5 from the end portion of the weld zone toward the inside of the nugget is analyzed by area analysis, and the proportion of the region in terms of area in which the concentration m (mass %) of P is more than twice the concentration M (mass %) of P of a base metal composition is 5% or less.

Abstract: An indirect spot welding method is provided in which, in indirect spot welding, nuggets formed in a fused state can be stably obtained. In the indirect spot welding method, the welding time is divided into two time periods t1 and t2, where electrode force F1 and current C1 are applied in the first time period t1, and electrode force F2 lower than electrode force F1 and current C2 higher than current C1 are applied in the next time period t2.

Abstract: In carbon dioxide arc welding by use of shielding gas comprised of carbon dioxide as main component, a welding wire that enables spray transfer of globules, and provides an excellent bead shape in addition to reduction of amount of spatters even in a high-speed welding, and a welding method using the welding wire are proposed.

Abstract: An aluminum alloy sheet combining excellent press formability and spot weldability is disclosed. A chromate film of about 1.0 to 50.0 mg/m.sup.2 expressed in terms of metallic chromium is formed as a first layer on an aluminum alloy sheet, and an organic resin film containing about 60-95% by weight of organic lubricant and having a thickness of 0.02 to 0.90 .mu.m in terms of dry thickness is formed as a second layer on the chromate film. As the organic lubricant, a high-density polyethylene having a mean molecular weight of about 900 to 15,000 and a density of about 0.93 g/ml or more is preferable. This aluminum alloy sheet can be effectively used for automobile body applications.

Abstract: A method including preparing an aluminum scrap containing a total of about 0.3 to 2.0 wt % of Fe and Si; melting and then adjusting the material composition so as to attain an Mg content of about 3 to 10 wt % or a composition further containing at least one of the elements Cu, Mn, Cr, Zr and Ti, each in the amount of 0.02 to 0.5 wt %; subjecting the material to casting, hot rolling, cold rolling and continuous annealing to obtain an aluminum alloy sheet having a tensile strength of about 31 kgf/mm.sup.2 or more; and applying a lubricant surface coating to impart a coefficient of friction of not more than about 0.11.

Abstract: A surface-treated aluminum material comprising an aluminum or aluminum alloy substrate, a chromate film deposited on the substrate, and an organic resin mixture film deposited on the chromate film is provided. The chromate film is deposited to a coating weight of from 5 to 100 mg/m.sup.2 calculated in terms of elementary chromium on the aluminum substrate. The organic resin mixture film is deposited to a dry film thickness of from 0.05 to 3.0 .mu.m, and comprises (a) 100 parts by weight of an organic resin, (b) 0.5 to 40 parts by weight of a powder lubricant having an average particle size of from 0.05 to 20 .mu.m, said average particle size being in the range of from 1.0 to 10 folds of the dry film thickness, and (c) 1.0 to 40 parts by weight of electroconductive finely divided particles having an average particle size in the range of from 0.05 to 5 .mu.m, said average particle size being in the range of from 1.0 to 2 folds of the dry film thickness.