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Aluminum (1050) was deformed by plane strain compression (PSC) up to 75% reduction. The total deformation conditions include four temperatures (from 150oC to 300oC) and two strain rates (5¡Ñ10-2s-1 and 5¡Ñ10-4s-1). After the deformation, the specimens were examined by TEM for observing the morphology of the microstructures and measuring various parameters, which includes the sizes and aspect ratios of dislocation cells, as well as the distribution of misorientation angles for dislocation walls.

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In our research, aluminum (1050) was deformed by plane strain compression (PSC) up to 65% reduction. The total deformation conditions include four temperatures (from 150oC to 300oC) and two strain rates (5¡Ñ10-2s-1 and 5¡Ñ10-4s-1). After the deformation, the specimens were examined by TEM for observing the morphology of the microstructures and measuring various parameters, which includes the sizes and aspect ratios of dislocation cells, as well as the distribution of misorientation angles for dislocation walls. At last, the proportions of GNBs and IDBs were tried to be determined.

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Equal channel angular extrusion (ECAE) has attracted a substantial attention for it provides the opportunity to introduce large plastic strain into the material in the bulk form. Both die angles and processing routes have been recognized as the important parameters in applying ECAE to fabricate ultrafine-grained materials. Unfortunately, studies of different group provided inconsistent conclusions on the effectiveness of processing routes, which are believed to be due to the incomplete microstructural information obtained in each investigation. In the present work, quantitative analysis of the microstructure developed by different processing conditions were conducted using transmission electron microscopy (TEM), in which the morphology, size, and shape of subgrains as well as boundary misorientation were fully characterized. A commercial pure aluminum (AA 1050) was deformed by ECAE to strain of ~ 8 with different routes (A, Bc and C, in terms of reorientation angle 0o, 90o, and 180o respectively of the billet between two extrusion passes) and die angles. The results show that the effectiveness of high angle boundary (HAB) formation is in the sequence of route A¡ÜBc>C. However, in terms of grain refinement, the effectiveness is in the order of route Bc>A>C. In addition, route A produces subgrains with the most elongated shape, while route Bc produces subgrains with the most equiaxed shape. These results may be attributed to the different shear pattern introduced in each route. ECAE die angle determines both the strain per pass and the shear plane orientation. In route C, the shear is maintained in the same plane and the effect of strain per pass can be studied. With route C, both the 90o and 120o die produce microstructure with similar HAB proportions, but they result in different arrangement of HABs. The 120o die produces subgrains with larger size and higher aspect ratio than the 90o die does in route C. Generally speaking, for the die angle range studied, the different values of strain per pass used in ECAE mainly affect the morphology of the subgrains. On the other hand, the effect of die angle is weakened with route Bc as compared to route C, which may be attributed to the intersection of shear planes involved in route Bc.

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It has been shown that alloys with submicron-grained structure can be produced by severe plastic deformation (SPD). However, our understanding about the characteristics of mechanical behaviors of these materials is still limited. According to the literature, many alloys exhibit quite different mechanical properties as the grain size decreasing to submicrometer range. In this study, commercial purity aluminum (AA1050) of grain size ranging from 0.35 to ~ 45 mm was obtained by the proper combination of equal-channel angular extrusion (ECAE) and annealing treatment. The influences of grain size, testing temperature and boundary character on the mechanical properties were studied in this work. Generally speaking, the materials of grain sizes below 1mm have quite different mechanical properties than those of coarser grain sizes. In tensile tests, they exhibited yield drop immediately followed by work softening at RT, while they showed Lüders extension followed by work hardening at 77K. In addition, their yield strength at RT was about 20% higher in compression than in tension. The submicron-grained aluminum has much higher strength but lower tensile ductility than large grained aluminum at room temperature, while it exhibits both high strength and good ductility at 77K. This finding suggests that the poor tensile ductility of submicron-grained alloys at room temperature may be improved by reducing the dynamic recovery rate. The Hall-Petch slope in the submicrometer grain size range showed positive deviation from that extended from coarser grains at both room temperature and 77K. This might be arisen from the phenomenon of inhomogeneous yielding as grain size below 1 mm. In addition, the grain boundary character distribution was found to have influence on the tensile properties of matrials of submicrometer grain sizes. As the grain size increases to the range between 1 mm and 4 mm, the tensile deformation at RT proceeds by the propagation of Lüders band initially, and followed by strain hardening. For materials of grain sizes greater than 4 mm, a normal strain hardening behavior of coarse-grained aluminum resumes.

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