Effects of excess magnesium or silicon on the two-step aging behavior of Al-Mg<sub>2</sub>Si alloys

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  • Ａｌ‐Ｍｇ?S２?TＳｉ合金の二段時効現象に及ぼす過剰マグネシウムおよびけい素の影響
  • Al Mg2Si ゴウキン ノ ニダン ジコウ ゲンショウ ニ オヨボス カジ

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Abstract

Al-0.7 and 1.2%Mg2Si alloys (balanced alloys) and those containing excess Mg or Si (excess alloys) were investigated by means of hardness, electrical resistivity and specific heat measurements and high-resolution transmission electron microscopy. The alloys were completely solution-treated at 560°C, quenched, preaged at 20-100°C, and finally aged at 175°C. If preaged at low temperatures, the maximum hardness of the alloys two-step aged is generally inferior particularly in the excess alloys to that of the alloys aged usually at 175°C, because of the coarsening of needle-shaped G. P. zones. If the excess alloys are preaged at high temperatures, the maximum hardness is somewhat lower. It is suggested in the excess alloys that the amount of clusters formed during preaging increases, but most of them are impossible to transform into G. P. zones, because of their compositions and structures considerably apart from those of G. P. zones. The two-step aging is effective in the low Mg2Si balanced alloy in which precipitates are uniformly distributed.

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