Abstract
The present investigation has been carried out to ascertain the cause of the age-hardening of Duralumin and 24 S-type Super-duralumin. These alloys age-harden marked by at room temperature when they are quenched from such a temperature as 500°, but the Al alloys containing Cu or Mg2Si do not show at room temperature such a marked age-hardening. The cause of the age-hardening of Duralumin and 24 S-type Super-duralumin is explained to be due to the decrease of the solid solubility of Cu or Mg2Si in Al with the fall of temperature similarly as those of the alloys containing Cu or Mg2Si. However, this elucidation does not apply to the age-hardening of Duralumin at room temperature, and to the necessity, of tempering of the alloys containing Cu or Mg2Si at 150-170° to attain the max. hardeness. The chill cast alloyss corresponding to the 8 sections cut through the Al-axis were prepared, and after annealing at 500° for 16. hours they were quenched in water and aged at room temperature. The change of hardness during the ageing was measured with a Brinell tester. The hardness test indicates that the alloys containing Cu only do not show any marked in-crease of hardness by the ageing at room temperature, but the addition of Mg to Al-Cu alloys gave a considerable influence upon the natural age-hardening, and that the phenomenon of ageing of the alloys containing more Cu than the ratio 4:1.5 in Cu and Mg is somewhat different from the alloys containing more Mg than the same ratio. The alloys containing more Mg than this ratio show less age-hardening at room temperature. By tempering at 50° and 100° immediately after quenching, the alloys containing Cu more than the ratio Cu: Mg=4:1.5 did not show as much hardening as at room temperature, but the alloys containing Cu and Mg in the ratio 4:1.5 to 1:1 were hardened rather remarkably by the tempering at 100°. From the diagram of Al-Cu-Mg alloy system pub-lished previously, the author concludes that the age-hardening of Al-rich Al-Cu-Mg alloys takes place on the course of the precipitation of a ternary compound Al13Cu7Mg8 denoted S, or CuAl2 and this ternary compound from Al-solid solution.
