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A tube of 6061 aluminum alloy in a T6 temper, precipitation-hardened with Mg2Si, was examined after irradiation in the core of the High Flux Isotope Reactor to fluences up to 1.3 × 1023 neutrons (n)/cm2 (0.1 MeV) and 3.1 × 1023 n/cm2 (thermal) in contact with the cooling water at a temperature of about 55°C. The alloy displayed up to 2.5 percent swelling due mainly to a precipitate of transmutation-produced silicon of which more than 6 weight percent was formed. Some cavities were also observed. Tension tests in the temperature range 55 to 200°C showed radiation-induced increases in yield stresses and ultimate stresses of 50 to 80 percent; elongation was reduced from the range 10 to 15 percent to about 5 percent at 55C° and to about 3 percent at test temperatures above 100C°. The fracture mode ws changed from transgranular tearing around inclusions to a mixture of transgranular tearing and ductile intergradular separation. These changes are attributed primarily to the radiation-induced silicon precipitate. A rim of intergranular cracks formed at the originally oxidized surfaces of the tube during tension testing and became deeper with increasing neutron irradiation and increasing temperature.
radiation, neutron irradiation, aluminum alloys, tension tests, ductility, fracture, electron microscopy, swelling, cavities, transmutation-produced silicon precipitate
Research staff member, Oak Ridge National Laboratory, Oak Ridge, Tenn.
Metallurgist, Union Carbide Corporation, South Charleston, W. Va.