61S合金に於ける銅の効果に就て(第1報)

抄録

61S, which is a heat treatable high strength alloy, has the highest proof strength among Al-Mg₂Si group. It is a peculiar alloy containing Cu. as its main element, the percentage ranging 0.15-0.40, in spite of its high corrosion resisting property. Being unable to find any literature on the behavior of its Cu. element, I have made some tracings, the results of which were reported herein and can be summarised as follows:-
(1) Enumerated various wrought aluminum alloys of Al-Mg₂Si group. which are now being used in actual practice. Particularly I have measured the mechanical properties of sheets in 61S various temper conditions, namely F, O, T4 and T6, and tried to make sure what are the most adequate conditions for its heat treatment.
(2) To the composition of standard 61S, excepting Cu, Cu was added in various percentages. ranging from to 0.8. The material was rolled into 1mm. sheets. The variation in mechanical properties in accordance with the change in Cu content was measured under various temper conditions; namely as-rolled (F); annealed (O); solution treated and then quenched (W); naturally aged for 10 days after W treatment (T4); and tempered and artificially aged after W treatment (T6).
(3) As the result, it was cleared that tensile strength increased with the increase in Cu content for every temper.
(4) Proof strength for 0, T4 and T6 increases with the increment in Cu within the range of 0.08 to 0.17%, however the same does practically not increase even when Cu is added beyond the said limit.
(5) Elongation decreases suddenly with a minor increase in Cu content, but the rate of decrease is somewhat smaller beyond the limit of 0.1-0.2%, while the said rate has such a tendency to increase again rapidly above 0.6% of Cu content.
(6) The effect of artificial aging can be precieved in the increase of proof as well as tensile strength with the increase of Cu; especially within the range of 0.2 to 0.5% Cu the rate of hardening attains its highest value. Elongation remains almost constant.
(7) Summarizing the above results, I can easily understand that the lower limit of Cu for 61S was determined as of 0.15. However, I thought it rather overhasty to determine the upper limit of Cu content simply from the facts that the rate of herdening in terms of tensile and proof strength does decrease and also elongation decreases beyond the limit of 0.6% of Cu content. Only after having made through corrosion tests, I will come back to this matter again.