Outstanding ductility of high-strength ultrafine-grained aluminium at cryogenic temperatures

By decreasing the temperature of the tensile tests from 293 to 77 K, a drastic increase in ductility (elongation to failure ~ 40 % and uniform elongation ~ 25 %) was demonstrated for the first time, along with an increase in strength (yield stress ~ 235 MPa and ultimate tensile strength ~ 265 MPa) for ultrafine-grained aluminium structured by combination of equal-channel angular pressing and cold rolling with subsequent annealing. The increase in ductility at 77 K is accompanied by an increase in the strain hardening coefficient. The physical reasons for the significant increase in ductility at 77 K are discussed in comparison with the peculiarities of microstructure. The obtained combination of ductility and strength opens up prospects for the use of this material at cryogenic temperatures, as well as the application of cryogenic temperatures for the formation of its products of complex shapes.