Effects of Strain-Rate and Temperature on Mechanical Properties of Hot-Rolled Mg-14.3Li-0.8Zn β-Phase Alloy

Abstract

The hot-rolled Mg-14.3Li-0.8Zn (HR LZ141) alloy exhibits anisotropic tensile properties with an average value of the normal anisotropic parameter, r_avg, of 0.6. From microstructural observation, it is proposed that the mechanical fibering, which is caused by the preferred alignment of the small α-phase particles in the rolling direction, results in this anisotropic property. Both strain rate $\dot \varepsilon $ and temperature T influence the tensile properties. At 6.67 × 10⁻⁵ s⁻¹ to 6.67 × 10⁻² s⁻¹ and room temperature, the tensile properties are all linear and sensitive to the log-scale $\dot \varepsilon $. The strain-rate sensitivity exponent, m, is 0.055 at all testing $\dot \varepsilon $. The work-hardening exponent, n, is positive, and the higher the $\dot \varepsilon $ is, the larger the n-value is, but the increase in the n-value is quite low for $\dot \varepsilon $ < 3.33 × 10⁻⁴ s⁻¹ and $\dot \varepsilon $ > 6.67 × 10⁻³ s⁻¹. The yield point phenomenon appears in σ-ε curves at room temperature when $\dot \varepsilon $ = 6.67 × 10⁻⁵ s⁻¹, and at 343 K when $\dot \varepsilon $ = 3.33 × 10⁻³ s⁻¹. The work-softening phenomenon occurs at T ≥ 343 K with $\dot \varepsilon $ = 3.33 × 10⁻³ s⁻¹. The yield stress and UTS increase but the elongation decreases as the testing temperature decreases. The Charpy impact test indicates that different notch orientations influence the impact energy due to the formation of mechanical fibering, and the result of impact energy vs. temperature shows no significance of transition temperature.