Abstract
The author has studied the magnitude and distribution of internal stresses set up during the heat-treatment of aluminium alloys with special referrence to 25 S.
As the quenching media, three different rates of cooling by water, namely at 20, 50, and 100°, and by rape-seed oil at 20° were selected. The stresses induced by quenching in water at 20° proved to be the maximum and in boiling water the minimum. The trouble, however, is that the internal stresses cannot be reduced without simultaneously decreasing the mechanical properties which results a maximum of internal stresses. For 25 S-alloy the soy-bean oil at 20° gave the most beneficial effects, where neither remarkable decrease in the optimum strength nor dangerous amount of internal stress was found. Although the tempering following quenching indicates the limited removal of stresses, its amount is very small comparing with those when quenched in any adequate medium. The stresses seems to be more or less increased by heating at 170°, probably on account of the new stresses induced by precipitation phenomenon.
The resistance to corrosion is lowered with the increasing temperature of the tempering and quenching medium. It is also affected by the various kinds of medium.
The investigations were carried out by several other aluminium alloys and the possibility of relieving the internal stresses without giving deleterious effect on the properties of metals has been proved.
