| Summary: | 碩士 === 國立中山大學 === 材料與光電科學學系研究所 === 101 === Ultrafine-grained (UFG) Al-15wt%Zn and Al-5wt%Zn alloys were produced by equal channel angular extrusion (ECAE) with 120° die and 16 extrusion passes. The influence of extrusion temperature and deformation route on the microstructure and mechanical properties of these Al-Zn alloys were investigated.
As the extrusion temperature increases, the average grain size of the Al-15wt%Zn increases, and the dislocation density within the grains decreases. As the extrusion temperature increase from 100 °C to 200 °C, the fraction of high angle grain boundary (HAGB) reduces from 67% to 26%, and the hardness decreases from 74.8 Hv to 49 Hv, which could be attributed to an increased recovery rate with increasing extrusion temperature.
Comparing the microstructures resulted from route Bc and route C, it is noted that route Bc produces higher proportion of equiaxed grains, and route C results in more elongated grains. In terms of the efficiency of generating HAGB, route Bc produces higher proportion of HAGBs, which are uniformly distributed, while route C produces less HAGBs, which are mainly distributed in direction parallel to the extrusion direction.
As the extrusion temperature increases, the tensile strength of Al-15wt%Zn decreases due to increasing grain size, but a substantial increase in ductility is realized, which might be due to an increased proportion of HAGBs. Different extrusion route causes little difference in the strength of the Al-Zn alloy, but it affects the tensile elongation.
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