Al-1.3 wt%Mg₂Si合金の二段時効について

抄録

The two-step aging behavior of Al-1.3 wt%Mg₂Si alloy was investigated by measurments of changes of age-hardening and electric resistivity and by electron micrograph observation. The results obtained are summarized as follows.
(1) The maximum hardness of the specimen aged at temperatures below 200°C after pre-aging at room temperature was lower than that of the specimen without pre-aging. In the case of the final aging at 260°C, the maximum hardness of the pre-aged specimen was higher than that of the specimen without pre-aging.
(2) In the case of the final aging at temperatures below 200°C, the maximum hardness of the specimen pre-aged up to 500 min at room temperature decreased with rise in aging temperature, but that of the specimen pre-aged for more than 1500 min increased as the aging temperature and the length of the pre-aging time were increased.
(3) In the case of the pre-aging at 100°C, the maximum hardness of the pre-aged specimen was always higher than that of the specimen without pre-aging.
(4) The maximum hardness of the Al-1.3 wt%Mg₂Si alloy containing 0.03 wt%Sn was higher than that of Al-1.3 wt%Mg₂Si alloy: The negative effect of the pre-aging on the Al-1.3 wt%Mg₂Si alloy was reduced by the final aging at temperatures below 200°C and the positive effect of the pre-aging increased on the final aging at 260°C by the effect of the additional element Sn.
The above results can be explained by the assumption that GP zones precipitated during the pre-aging contain the quenched vacancy and are unstable but become stable as the time proceeds, and by the the fact that GP zone formation is suppressed by the addition of Sn and consequently the precipitation of an intermediate phase is accelerated.