| 摘要 |
PROBLEM TO BE SOLVED: To reduce weight and to improve welded strength by making the thickness of the recrystallized structure layer not more than a specified value at the outermost surface of an overlaying part in an Al alloy of a specific composition and thereby reducing the thickness of a crystallized layer formed in the heat affected part in welding. SOLUTION: An Al alloy is such that it contains 5.0-7.5% Zn and 0.5-1.0% Mg in wt.% and that, at the time of cladding by welding, the thickness of the recrystallized structure layer 6 formed in the heat-affected part is 20μm or less. The Al-Zn-Mg based alloy is an extruded material, in which a superior resistance against stress corrosion crack can be obtained by this cladding by welding. The recrystallized structure layer 5 at the outermost surface of the Al alloy is the layer 6 formed in the heat affected part that is heated at the time of cladding by welding. The recrystallized structure layer 5 is the surface opposite from the heat input surface at the time of cladding by welding, which is desirably performed at the electric current of 100-120 A, speed of 900-950 m/min., and Ar gas flow rate of 18-20 liter/min.
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