Nanograined Aluminum Prepared By Plastic Deformation And Its Thermal Stability

Nanostructured materials have attracted much attention due to their unique structure and excellent properties.Plastic deformation is one of the effective ways to prepare nanograined materials.However,it is difficult to effectively refine the microstructure of pure aluminum through general plastic deformation methods.In this study,1060 commercial nanograined pure aluminum was prepared by composite rolling and high pressure torsion at low temperature.The microstructure of the samples was characterized by means of optical microscope,scanning electron microscope,transmission electron microscope and electron backscatter diffraction.The mechanical properties of the samples were tested by microhardness.The effects of different deformation conditions on the microstructure and the stability of the nanograined sample were studied.The results are as follows:(1)Microstructure and mechanical properties of 1060 commercial pure aluminum cold rolled at low temperature.After rolling under liquid nitrogen,the saturation size of pure aluminum grains is 270 nm.Its morphology is mainly lamellar structure,and there are a large number of low-angle grain boundaries and dislocation structures.After rolling,the microhardness of 1060 commercial pure aluminum increases with the decrease of grain size.When the grain size is 270 nm,the hardness can reach 440 MPa.(2)Microstructure and mechanical properties of 1060 commercial pure aluminum prepared with high pressure torsion.The cold-rolled pure aluminum samples were subjected to high-pressure torsion treatment.This is the first time that equiaxed grains with a size of 70 nm were obtained in commercial pure aluminum.The grain boundaries in the nanograined sample are mainly high angle grain boundaries.A few twin boundaries can be detected as well.The hardness increased significantly to 840 MPa for the 70-nm grained sample.(3)Thermal stability of nanograined pure aluminum.The thermal stability of the nanograined Al is studied by annealing the samples at different temperatures.It is found that the grain size of the nanograined Al with grain size of 70 nm will be maintained smaller than 100 nm when the annealing temperatures lower than 200 °C,while the submicro-grains with grain size of 270 nm will coarsening significantly to 1 μm after annealed at 200 °C.