Microstructure and superplasticity of the as-cast Mg-9Al-1Zn magnesium alloy after high-ratio differential speed rolling

초록

The direct application of high-ratio differential speed rolling (HRDSR) on the cast microstructure of Mg-9Al-1Zn (AZ91) alloy resulted in significant refinement of grain size and divorced eutectic beta-phase with semi-network structure. Nanosized beta-phase particles (50-100 nm) precipitated at grain boundaries and within grains from the Al-rich alpha-phase, which formed as a result of fragmentation and decomposition of the divorced eutectic beta-phase during severe plastic deformation by HRDSR. The HRDSR-processed AZ91 alloy exhibited excellent superplasticity at low temperatures below 573 K. The optimum superplasticity (with a maximum tensile elongation of 830%) was achieved at 573 K at I x 10(-3) s(-1). Beyond 573 K, serious deterioration in superplasticity occurred due to a loss of thermal stability of grain size caused by the dissolution of the fine beta-phase particles into the matrix. Models that can explain the high-temperature flow behavior of the ultrafine grained AZ91 alloy were proposed. (C) 2016 Elsevier B.V. All rights reserved.

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