Age hardening of 24S type superduralumin containing Si and Mn was investigated by X-ray method using Cu K radiation. When the specimen, fixed to the camera and photographed successively, was quenched, the displacement and deformation of the spot due to ageing was observed. But they were not so remarkable as in the case of superduralumin containing no Si or Mn, which was reported in the previous paper.
The effect of tempering was next studied. The specimens were all cold-rolled after quenching from 550° and then tempered. In superduralumin containing no Mn or Si, precipitation of compound was not so remarkable when tempered at low temperature, and even 250°, long hours were required to attain equilibrium state. But if Si or Mn was added to ternary superduralumin, noticeable precipitation was observed even at 150°. Also in Al-Cu alloy containing 4% Cu, compounds were precipitated easily at 150°, Therefore, by the addition of Si or Mn to superduralumin, precipitation of compound from supersaturated solid solution becomes much easier, but the degree of ageing at room temperature decreases, and the type of ageing of superduralumin changes to that of Al-Cu alloys.
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