Al-Zn-Mg系合金抵抗スポット溶接部の時効挙動

A study was made on the aging behavior in a resistance spot weld of commercial Al-Zn-Mg alloys. Hardness measurements, X-ray small-angle scattering method and electron probe X-ray microanalysis were applied. The hardness increases not so much in the nugget as in the heat affected zone by post-weld aging at room or elevated temperatures. The hardness in the nugget increase with an increase in distance from the nugget center at any aging times and temperatures. Softened zone is observed in the heat affected zone near the fusion line by post-weld aging. These aging characteristics are also found in the resistance spot weld aged after solution treating for 1h at 465°C. The X-ray integrated intensity is always lower for the nugget center than for the heat affected zone during the aging after welding or after solution treatment. These results are attributed to the fact that there exist macro- and micro-segregations of solute atoms in the nugget of the resistance spot weld of commercial Al-Zn-Mg alloy.