7075アルミニウム合金圧延材の引張特性に及ぼす試験雰囲気の影響

抄録

Severe cold rolling was applied to a 7075 aluminum alloy and tensile tests were made to evaluate mechanical properties of the rolled specimens. The sheet specimens of 6.8 mm thick were solution-treated at 480°C for 1 h, water-quenched and subsequently rolled to 0.7 mm in thickness at room temperature. A part of the rolled sheet was solution-treated again, and heat treated at 120°C for 24 h (T6). Tensile test pieces were made from these sheet specimens and the tensile tests were made at initial strain rates of 1.67×10⁻⁶ and 1.67×10⁻⁷ s⁻¹ in dry nitrogen gas (DNG) and in humid air (HA) where the relative humidity was controlled to be above 90%. The ultimate tensile strength was about 640 MPa, which is far higher than the specimen treated in T6 condition, and it does not depend on initial strain rate and test environment. It is noted that the specimen tested in the humid air shows relatively high elongation at the lower strain rate of 1.67×10⁻⁷ s⁻¹. This result indicates that the cold-rolled specimen has excellent resistance to hydrogen embrittlement in humid air.