Study On The Microstructure And Properties Of High Purity Aluminum By Equal Channel Angular Pressing

The grain size of ultra- fine grain materials is very small so that compared with common materials, the proportions of the ultra- fine grain metastable state grain boundary and the low-angle grain boundary are large, and further the physical property and mechanical property of ultra- fine grain materials are normally different from traditional materials. The equal channel angular pressing technology is a method of realizing severe plastic deformation of grain refinement through pure-shear deformation. Compared with other methods, equal channel angular deformation is easy to operate, simple in process and low in cost, thereby being regarded as the most promising refined grain technological method.This paper aims to study the pressed high pure aluminum grain refinement mechanism and the change rule of high pure aluminum grains along with the increasing of the pressing passes through high pure aluminum multi-pass equal channel angular pressing tests. Furthermore, this paper also studies the influence law of pressing passes and pressing paths on the mechanical property and corrosion resistance of high pure aluminum.After one to eight passes of equal channel angular pressing deformations, high pure aluminum grains were refined continuously, the proportions of equiaxed grains and high-angle grains increased gradually, and the interior structure homogeneity of the sample was improved continuously. After the first pass processing, interior grains in the sample were stretched, with a great number of substructures appearing in the grains. After the second pass processing, the size of interior grains of the sample was reduced obviously, and meanwhile the high-angle boundary began to appear. During the fourth pass processing, equiaxed grains appeared in the sample, and the proportion of the high-angle boundary was improved greatly.After the Bc path and the C path were subjected to equal channel angular pressing, the hardness increased continuously along with increasing of the pressing passes. The high pure aluminum sample of Bc path subjected to 1-8 passes of equal channel angular pressing had a good heat stability when annealed at 100 DEG C; when annealed at 200 DEG C, the heat stability kept good in the first four passes of equal channel angular pressing but became worse in the last four passes of equal channel angular pressing. The sample of C path subjected to 1-8 passes of equal channel angular pressing had a good heat stability after annealed at both 100 DEG C and 200 DEG C. The compressive test result indicates that the sample subjected to equal channel angular pressing showed an obvious elastic stage in the compression process, and the compression resistance of the sample is improved continuously along with increasing of the pressing passes. The tension test result indicates that the tensile strength of high pure aluminum reaches the maximum value at the third pass. After scanning analysis of fractures of all passes of stretching samples, the result shows that the fracture mode of the 1-8 passes of the stretching samples are all ductile fracture. The high pure aluminum has the best corrosion resistance after the first pass of equal channel angular pressing, and has an obviously better corrosion resistance than the original annealed high pure aluminum.After pressing, not only good plasticity and corrosion resistance of the high pure aluminum are kept but also the hardness and strength of the high pure aluminum are improved greatly. After comprehensively considering the mechanical property, corrosion resistance and grain size of samples at all passes, the result is that the comprehensive property of the high pure aluminum sample at the fifth pass is the best. The reason is that the high pure aluminum material at the fifth pass has high hardness and strength, good plasticity and better corrosion resistance than the annealed high pure aluminum.