Tailoring The Microstructures And Mechanical Properties Of Cryogenic Rolling Aluminum Alloy And Metastable Austenitic Stainless Steel

The advanced cryogenic deformation can effectively suppress the thermal activation during the deformation process at low temperature to accumulate the high density dislocation.so as to promote the microstructure refinement and the performance improvement.Therefore cryogenic rolled is a hopful manufacturing method for the structural metals and has widly industrial application.However,the deformation mechanism,the microstructure and texture evolution,the annealing behavior and the recrystallization mechanism are still not clear and at the exploratory stage.The basic research on the development of cryogenic deformantion can provide the theoretical and techanincal support for the practical application.In order to clear the microstructure and texture evolution,deformation strength mechanism,the recrystallization behavior and mechanical properties of the face-centered cubic(FCC)metallic materials,the typical commercial 5052 Al alloy and 304 austenite stainless were selected as a model metal in the present work.The microstructure/texture evolution,deformation/strengthening mechanism and annealing recrystallization behavior of two different alloys under the cryogenic rolled(CR)and room temperature rolled(RTR)were comparative studied.For austenitic stainless steels with phase transition,the quantitative analysis of the deformation induced martensitic transformation,the transformation mechanism and the behavior of grain refine were studied.The study found that the CR could rapidly accumulate high density dislocation and form more deformation bands and shear band thand the RTR,which the CR could improve the yield and tensile strength of 5052 A1 alloy.The main reason for performance improvement of CR was the dislocation strengthenging and the grain boundary strengthening.However,the strength difference between the sheets made by the two deformation methods would decrease as the increase of deformation.The reason that the preformation different between CR and RTR decreased was that the dislocation density would tend to saturation at high deformation.During the recrystallization and subsequent annealing,the retained high-density dislocations and the high distortional energy in the CR samples would provide higher recrystallization driving force and more valid nucleation sites.This was helpful to the finally grain refinement so as to effectively improve the mechanical properties of the material.The TS and YS values of the post-annealed CR 5052 Al alloy are～30 MPa higher than those of the RTR alloy without elongation loss.The mechanical properties are better than the commercial 5052 and reach the properties of high grade 5000 alloy.In addition,the cryorolling could optimize the distribution of the rolling texture of 5052 A1 alloy,the main components being Brass {011}<100>.Copper {112}<111>and S {123}<634>.This makes it possible for the textures to be more evenly distributed at the later stage of recrystallization,and eventually form the lower strength recrystallization textures.Therefore the samples with weak texture components can improve the formability.For the other typical FCC metal 304 austenitic stainless steel,the cryorolling can significantly promote the martensitic transformation thus obviously improve the uniformity of the rolled sheet in the direction of thickness.The orientation relationship between the transformed martensite and the austenite in the cryogenic and room-temperature rolled sheets can still keep the K-S(Kurduumov-Sachs)relationship.The large amount of martensite induced by CR is not only helpful to the grain refinement during annealing,but also enhances the phase transformation strengthening during the deformation.However,for the RTR,the strengthening mechanism is dominated by dislocation strengthening.By refining the grains,the tensile and yield strength of CR after recrystallization increase by～11.7%and～47.4%compared with the RTR.respectively.