| Enhancement of the ductility is very important for the successful commercialization of magnesium alloys. Among other methods, this can be achieved by refining the grain structure through equal channel angular pressing (ECAP) or extrusion. Preliminary work was conducted using as-cast AZ-31, but this was found to be of low ductility and extruded bars were used for the rest of the experimentation. These were annealed at 350°C for 1 hour and extrusion was carried out at three temperatures, 200, 250 and 300°C, using routes A, BC and C at a speed of 5 mm/s for up to 8 passes. It is apparent that increasing the operating temperature increases the final grain size as a result of grain growth. Conversely increasing the number of passes results in a finer grain size because of the accumulation of shear. However, grain growth can affect the final grain size for all three routes. After one ECAP pass, a preferred orientation with the basal planes inclined at 45° to the ECAP axis is observed. For route A, as more and more passes are employed, the original fiber texture tends towards a rolling texture. By contrast, for route C, repeating the ECAP steps does not change the texture, which retains the 45° preferential orientation. The mechanical properties indicate that using a path with shearing in more directions, such as route C, results in increased ductility, with a wider flow curve than for route A. As the temperature of ECAPping is increased, the strength of the extruded product increases and the ductility decreases. This appears to be due to the coarser grain size of the 300°C product and indicates that the effect of grain refinement is greater than that of texture. |
