Effect of Neutron Irradiation on Cryogenic Temperature Strength of Aluminum Alloys and Their Electron Beam Welded Joint

Effects of a neutron irradiation on mechanical properties of aluminum alloys have been studied using a miniature tensile testing method. In a present study, the aluminum alloys (A7N01, A5083 and A6061) for cryogenic structural materials were selected as the testing materials, and their base metals and electron beam welded joints were tested at cryogenic temperatures. Results obtained are as follows: (1) Tensile strength of base metals and welded joints became higher in the order of A7N01, A5083, and A6061, and their elongations became larger in the order of A5083, A6061 and A7N01 after neutron-irradiated up to 1.7×1023n/m2. (2) All the materials exhibited large serrations in the nominal stress-nominal strain curves at 4.2 K. Little effect of neutron irradiation on the serration was observed. (3) The base metal and the welded joint of A7N01 exhibited high strength at cryogenic temperature. Increase of strength by the irradiation was larger for the welded joint than the base metal. Decrease of ductility at cryogenic temperature by the irradiation was larger for the base metal than the welded joint. Both the base metal and welded joint became sensitive to the existence of a notch with the increase of a neutron fluence. (4) The neutron irradiation up to 1.7×1023n/m2 exhibited little effect on the strength of the base metal and the welded joint of A5083. Ductilities of the base metal and welded joint decreased slightly with the neutron irradiation. (5) Strength of the base metal of A6061 was little affected by the neturon irradiation, but the welded joint showed the increase of strength which was considered to be due to the effect of aging during the neutron irradiation. Sensitivity to the notch of the base metal and the welded joint increased, and notch toughness of the base metal and welded joint decreased with increase of the neutron fluence.