Mechanical properties and microscopic mechanisms of 2219-T6 aluminum alloy under dynamic tension with cryogenic temperatures

The 2219-T6 aluminum alloy has poor plastic deformation ability at room temperature, which makes it difficult to satisfy the forming requirements. This study combined high strain rate and cryogenic temperature to improve the formability of aluminum alloys. Dynamic tensile experiments using Split-Hopkinson tensile bar combined with cryogenic temperatures have shown that the ultimate strength and fracture elongation at 2000 s^-1 with -160 °C is 482 MPa and 29.0%, respectively, representing a substantial increase of 31% and 125%, respectively, compared to quasi-static tension at 25 °C. By analyzing the microstructure, the results show that more uniform micro-deformation behaviors occurred due to the activation of multi-slip at high strain rates with cryogenic temperature. The high strength is due to the formation of a multitude of dislocations and substructures. Dislocation networks caused by the increasing cross-slip frequency increase the strength and guarantees stable plastic flow. It also leads to local shear fractures due to the increased velocity of dislocations movement and inhibited propagation of voids. This study provides the fundamental researches for understanding the superior mechanical properties of high-strength aluminum alloys at cryogenic temperatures in the area of high-speed forming and for addressing the challenges associated with forming these alloys directly in their service state.