Flow behaviors and deformation mechanism of WQ-tempered Al-Li alloy at cryogenic temperatures

Cryogenic forming is a promising technique for fabricating complex components using high-strength aluminum alloys. In this work, the flow behaviors and microstructure evolution of a WQ-tempered (solution treatment followed by water quenching) 2195 Al-Li alloy was studied by uniaxial tension tests from -196 to 25 degrees C and strain rates from 2.5 x 10(-4) to 1 x 10(-2) s(-1). The results showed that the ductility gradually increased after decreasing the deformation temperature, while the strain rate had a limited effect on the ductility. Serrated flow caused by dynamic strain aging occurred from -60 to 25 degrees C, which increased the flow stress due to additional pinning of mobile dislocations by solute atom clusters. Smooth flow curves were obtained from 196 to 90 degrees C due to the suppression of dynamic strain aging. The microstructure observations indicated that more homogeneous plastic strain and grain rotation occurred in the cryogenically-deformed sample, leading to the formation of weaker fiber texture compared with the sample deformed at room temperature. A higher work hardening rate was achieved at cryogenic temperature, which delayed local necking. The suppression of serrated flow and homogeneous plastic deformation significantly improved the ductility at -196 degrees C, with a uniform elongation of 35.2%, which was 84.3% higher than that at 25 degrees C.