Study On Microstructure Adjustment And Control During Cold Rolling Of Al-2%Cu To High Strain

Severe plastic deformation is one of the effective methods for preparing nanostructured metals.However,when the strain reaches a certain level,the structural coarsening caused by the dynamic recovery of the deformed nanostructure and the structural refinement caused by the deformation reach a balance,and the microstructure cannot be further refined by increasing the strain.For pure aluminum or low alloy Al alloys,the boundary spacing of this balanced structure is about 200 nm.Therefore,how to effectively hinder the dynamic movement of the boundary and suppress the dynamic recovery during the high strain deformation process becomes the key to whether the plastic deformation can further refine the structure.In this paper,an aluminum-copper alloy with 99.999% pure aluminum and 2%pure copper is selected as the experiment material.The material after solution treatment was cold rolled to high strain.In order to obtain a finer structure and better mechanical properties of nano-layered sheet Al-2% Cu material,intermediate annealing was used to control the second phase particles precipitation,and storage at room temperature for a long time was used to promote the grain boundary segregation of solute atoms during the cold rolling process.Characterization of microstructure evolution during deformation by transmission electron microscopy,and testing of mechanical properties by means of micro-hardness,tensile testing,etc.The main conclusions are as followed:(1)As strain increases,the structure gradually forms a layered structure with a large number of dislocation interfaces.The average boundary spacing of the structure continuously decreases with increasing strain.When the material was cold-rolled to98% reduction,the average boundary spacing of the Al-2% Cu reaches 139 nm,the effect of strain on the refinement of the microstructure is saturated.If the strain continues to increase,the microstructure will not be further refined,and the microhardness of the material will not change.(2)When the material was cold rolled to 75% reduction,the layered nanostructure has been basically formed.After the sample was annealed at 100 ° C for 30 minutes,a large amount of second phase particles were formed in the matrix,and more precipitates were found on the grain boundaries.After annealing,the samples were cold-rolled to a total deformation of 98%,the structure was further refined,and the average boundary spacing reached 113 nm.It shows that the second phase particles effectively hinder the boundary movement.The sample was further cold rolled to a total deformation of 99.4%,the average boundary spacing reached 116 nm,indicating that the strain refinement effect on the structure was saturated again.(3)After the material which was directly cold rolled to 98% reduction was stored at room temperature for 1 year,the Cu atoms in the matrix were significantly segregated.When material was further cold-rolled to 98.4%,the average boundary spacing of the layered structure reached 129 nm indicating further refinement was occurred.This showed that the grain boundary segregation of solute atoms can also promote the refinement of the microstructure during deformation.(4)After the intermediate annealing,the material cold-rolled to 98% reduction was stored at room temperature for 8 months,and then further cold-rolled to a total deformation of 98.6%,and the average boundary spacing was reduced to 83 nm,indicating that under the combined effect of the precipitated particles and the element segregation the organization will be more refined.The yield strength and tensile strength of the material at this time were 420 MPa and 430 MPa,respectively.