| 摘要 |
PROBLEM TO BE SOLVED: To obtain a welded material having excellent strength by suppressing re-precipitation of Mg2 Si in which Mg and Si solid-solved in a matrix by welding heat do not contribute to the improvement of the strength. SOLUTION: Immediately after an Al-Mg-Si alloy aging treated material containing 0.3-1.0% Mg, 0.5-1.5% Si, 0.1-1.0% Cu and 0.05-0.35% Fe and further, one or two or more kinds of 0.1-0.6% Mn, 0.1-0.4% Cr and 0.1-0.3% Zr under the condition of Mn%+Cr%+Zr%=0.15-0.80% and in which the quality of Mg2 Si is >=1.0%, is welded under the condition where a head affected part is partially heated to >=400 deg.C, the material is cooled at the cooling speed of >=30 deg.C/sec. to the temperature of <=300 deg.C. The quality of Mg2 Si is regulated to >=1.1% when an excessive Si quantity to be calculated as [Si%-0.58%×Mg%] is <=0.2%. Thereby, Mg2 Si is precipitated by a natural or an artificial aging after the welding and the strength of a welded part is recovered.
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