Al-Mg-Si合金の二段時効に関する一考察

抄録

Two-step aging phenomena in an Al-1.17%Mg₂Si alloy pre-aged at 20-100°C and finally aged at 175°C were studied by means of hardness anal electrical resistivity measurements and transmission electron microscopy. The positive effect of two-step aging is visualized only for pre-aging at 100°C, and in this case, hardness drop or coarsening of G.P. zones is never found under the condition of short time pre-aging. The number of clusters formed during pre-aging increases with lowering pre-aging temperatures. The clusters do not easily change into G.P. zones during final aging and almost remain unchanged for a prolonged time, as pre-aging temperatures lower. These facts are incompletely understood basing on the previous model so far proposed. It is likely that the effect of two-step aging in this alloy is related to the structure difference between clusters and G.P. zones. The difference is reduced with increasing pre-aging temperatures, so that the clusters change into the zones more easily accompained with the positive effect.