抄録
From the investigation of the constitution Al-Cu-Mg alloy system the author found the existence of a ternary compound called “S” to be in equilibrium with Al-solution as reported in a previous paper. The age-hardening of Duralumin and 24 type Super-duralumin was considered to occur in the course of the precipitation of this ternary compound from Al-solid solution. To confirm this consideration, the present investigation has been made on rolled Al alloys containing Cu and Mg, and he confirmed the similar phenomena of ageing observed on cast alloys.
Immediately after quenching from 500° the change of dilatation on tempering was measured. The alloy containing Cu only showed a marked expansion from about 210° and subsequent contraction from about 280°. This change of dilatation was considered to be due to the separation of CuAl2. But the alloy containing Cu and Mg showed an expansion and contraction below 100° and the marked change of dilatation from 200° due to the precipitation of CuAl2 was also observed in an alloy containing about 0.5%. However, the alloys containing 1.5% of Mg and 4% of Cu did not show the irregular dilatation due to the precipitation of CuAl2. Therefore, the author has concluded that the expansion and contraction below 100° are due to the precipitation of S-compounds. This phenomenon was not found in the specimens aged for 1 week.
The effect of a small content of Si upon the ageing of Al-alloy containing Cu 4% and Mg 1.5% was studied on rolled alloys. Si did not accelerate the age-hardening of quenched alloys, but the alloys containing 0.6-0.8% Si showed considerable hardening when they were tempered at 150° for 10 hours. The effect of Si upon such Al alloys was discussed from the constitutions of Al-Cu-Mg-Si alloy system. The difference of the ageing-phenomenon is due to the fact that the equilibrium relation displace to the Al-CuAl2-Mg2Si-Si from Al-CuAl2-S-Mg2Si. This fact was proved by similar dilatation curve of these quenched alloys as those ones containing Cu only.
