Cryogenic thermal conductivity of 7050 aluminum alloy subjected to different heat treatments

Abstract

The cryogenic thermal conductivity of high-strength 7050 aluminum alloy subjected to the processes with different combinations of solution, aging and deep cryogenic treatment, was measured by a one-dimensional steady-state thermal conduction method. The microstructure evolution of this alloy after different treatments was also characterized to investigate the changes in thermal conductivity. The results showed that the thermal conductivity of aluminum alloy was approximately linearly reduced with the decrease of temperature in general. Under the effects of different treatments, it was found that the thermal conductivity at different temperatures was sharply decreased by 30% after solution. Deep cryogenic treatment further decreased the thermal conductivity when it was conducted after solution. However, the conduction of aging increased the thermal conductivity after solution or solution-deep cryogenic treatment. Intensive lattice distortion and abundant of point defects that enhanced the electro scattering were the main reasons for decreasing the thermal conductivity after solution. The relatively large size of Al-Cu precipitates and increased dislocation density contributed to the further decrease of thermal conductivity after deep cryogenic treatment. The precipitation of a large number of ultra-fine secondary phase particles after aging increased the thermal conductivity by sufficiently releasing the lattice distortion. This work also provided an efficient method for investigating the mechanisms of deep cryogenic treatment on aluminum alloy by studying the thermal conductivity at low temperatures.