ＥＣＡＥ加工したＭｇ‐Ｌｉ‐Ｚｎ合金の引張特性および低温超塑性の発現

Abstract

In this study, repetitive ECAE processing was applied to Mg–Li–Zn alloys with dual phases consisting of α (Mg solid solution) and β (Li solid solution) phases in order to improve their tensile properties and to achieve low temperature superplasticity by refining both phases and spheroidizing α phase. Such a microstructural change in α. phase is reached by 2–pass ECAE processing at 293 K for LZ101 alloy and 323 K for LZ81 and LZ91 alloys, and subsequent annealing for 1 h at 623 K for LZ81 and LZ101 alloys and 673 K for LZ91 alloy. 4–pass ECAE processing at 293 K for LZ101 alloy and 323 K for LZ81 and LZ91 alloys and subsequent annealing at 398 K for all of the alloys results in grain refinement of β phase. As a result the specimens tested at 293 K show better tensile properties than as-rolled ones. The elongation of as-ECAE-processed specimens tested at 373 K reaches approximately 400% under a relatively low strain rate of about 10−4 s−1 together with low flow stresses, and the specimens have the relatively high strain rate sensitivity exponents of about 0.4. Microstructures of the specimens after tensile test at 373 K reveal that dynamic recrystallization and precipitation occurs in both phases. These results suggest that an increase in grain boundary area through the fine recrystallized grains and precipitation of β phase on the recrystallized grain boundaries of α phase contribute to grain boundary sliding, resulting in the occurrence of superplasticity at 373 K, which is lower than Tm/2.