Study of the microstructures and tensile properties of Al6061-T6 irradiated with a mixed spectrum of high-energy protons and spallation neutrons to ∼10 dpa

Considering the application of Al6061-T6 as the proton beam window in an accelerator driven facility like a spallation neutron or muron source, Al6061-T6 was irradiated in Target-10 of the Swiss Spallation Neutron Source. Three tensile specimens were irradiated up to 11.1 dpa with the products of 540 appm He and 1320 appm H at 93 °C with a mixed spectrum of high-energy protons from the accelerator and spallation neutrons generated in the target. The specimens received an irradiation dose of around 10 dpa (displacement per atom). The microstructures of specimens in three conditions, as-received (AR), as-irradiated (AI) and post-irradiation annealed (PIA), were investigated. In the AI specimens, not only high-density nanoscale dislocation loops and bubbles were generated, but the complex structures of needle-shaped nanoscale Mg and Si precipitates and large Si, Fe, Mn and Cr precipitates also changed significantly. This was manifested in a substantial reduction in the number of needle-shaped precipitates and the formation of some small precipitates near the large precipitates. After the post-irradiation annealing at 152 °C for 1 h, the needle-shaped precipitates recovered, but the high-density bubbles remained. Tensile tests revealed the decrease in total elongation up to about 50% after irradiation, from ∼ 10% for the as-received specimens to ∼ 5% for the irradiated specimens.