Mechanisms on the outstanding high temperature plasticity of AlNp/Al-0.4Cu composites induced by cryogenic treatment

The 8.2AlNp/Al-0.4Cu composites were solution treated by heating to 530 °C for 1 h and then quenched in water and liquid nitrogen, respectively. After quenching in liquid nitrogen, the composites possess nearly the same ultimate tensile strength (UTS) but a significant increase in elongation by 79% (at 350 °C) compared with that of the samples quenched in water. The impact of different quenching process on the microstructure evolution and high temperature tensile properties has been investigated systematically. After quenched in water, there are 69% low-angle grain boundaries (LAGBs), high point defect concentration and a small quantity of dislocations. This microstructure leads to the dynamic recrystallization as well as discordant deformation. The high percentage of high-angle grain boundaries (HAGBs), high dislocation density and low point defect concentration of the composites (quenched in liquid nitrogen) help improve the microstructural stability and contribute to the favorable elongation at 350 °C. The mechanisms revealed in this work may provide a paramount method to achieve a superior combination of strength and elongation for heat resistant Al alloys.