Abstract
Cryogenic deformation can improve the strength and plasticity of Al–Li alloy, although the underlying mechanism is still not yet well understood. The effects of cryogenic temperature on the tensile properties and microstructure of an Al–Cu–Li alloy were investigated by means of tensile property test, roughness measurement, scanning electron microscope (SEM), optical microscope (OM), electron backscatter diffraction (EBSD), and transmission electron microscope (TEM). The results indicated that the strength and elongation of the as-annealed (O-state) and solution-treated (W-state) alloys increased with the decrease in deformation temperature, where the increasing trend of elongation of the W-state alloy was more significant than that of the O-state alloy. In addition, a temperature range was observed at approximately 178 K that caused the strength of the W-state alloy to slightly decrease. The decrease in temperature inhibited the dynamic recovery of the Al–Cu–Li alloy, which increased the dislocation density and the degree of work hardening, thus improving the strength of the alloy. At cryogenic temperatures, the internal grain structure was more involved in the deformation and the overall deformation was more uniform, which caused the alloy to have higher plasticity. This study provides a theoretical basis for the cryogenic forming of Al–Li alloy.
Highlights
Al–Li alloys have a high specific stiffness and strength [1,2]
Kumar et al [12,13,14] studied the difference in tensile properties between cryogenic rolling and room-temperature rolling and found that the yield strength and tensile strength of cryogenic-rolled alloys were significantly higher than those of room-temperature-rolled alloys
It was suggested that fracturing at cryogenic temperatures was caused by the collapse of the dislocation grid under high stress
Summary
Al–Li alloys have a high specific stiffness and strength [1,2]. Due to the demand for lightweight structural materials for the aerospace industry, Al–Li alloys have become a hot research topic [3]. Cryogenic forming can significantly improve the strength and plasticity of aluminum alloy materials simultaneously [9,10,11], which is expected to become a revolutionary processing technology. Xu et al [16,17] studied the tensile properties and surface characteristics of 6000 series aluminum alloy at room and cryogenic temperatures and found that deformation at 77 K significantly improved the strength and elongation of the alloy. This was due to a higher strain hardening exponent and more uniform deformation mode at cryogenic temperatures. 2195 Al–Li alloy was tensile-tested at different deformation temperatures to determine its mechanical properties and study deformation behavior at cryogenic temperatures, and to explore the mechanism for the influence of cryogenic forming on the microstructure and properties of 2195 Al–Li alloy to provide a basic theoretical basis for the cryogenic forming of other Al–Li alloys
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