Effect of annealing temperature on the microstructure and mechanical properties of an as-rolled Mg--9wt.%Li--3wt.%Al--1wt.%Zn alloy sheet

Abstract

This study investigated the effect of annealing temperature on the mechanical properties of an as-rolled Mg--9.26wt.%Li--3.03wt.%Al--1.10wt.%Zn (LAZ931) alloy sheet. The dual-phase (α+β) LAZ931 alloy plate of 3 mm in thickness were rolled (67% reduction) and then annealed at temperatures at 100°C--350°C. The alloy's ductility showed a sharp concave downward tendency as a function of annealing temperature. The elongation of the LAZ931 alloy sheet increased with annealing temperature up to 150°C, followed by a sharp decrease of the alloy’s ductility as the annealing temperature higher than 150°C. The specimen exhibited an extremely low elongation (only ~0.5%) at annealing temperature around 300°C. Formation of brittle AlLi particles on boundary resulted in Li depletion zone near by grain boundary, transforming the Li depletion zone into α (hcp) layer. The combined effects including brittle AlLi particles on boundary and the hcp α layer on boundary resulted in the brittlement of the high-temperature-annealing sample.

Keywords

Mg--Li alloy / annealing / AlLi / embrittlement

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Acknowledgements

The authors are grateful to the SEM/X-ray Lab., NCHU for supporting the microstructural examination and X-ray diffraction experiments.

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2014 Higher Education Press and Springer-Verlag Berlin Heidelberg