Hot Deformation Behavior and Constitutive Analysis of As-Extruded Mg–6Zn–5Ca–3Ce Alloy Fabricated by Rapid Solidification

Abstract

The plasticity of Mg–6Zn–5Ca–3Ce alloy fabricated by rapid solidification (RS) at room temperature is poor due to its hexagonal-close-packed (HCP) structure. Therefore, hot deformation of RS Mg–6Zn–5Ca–3Ce alloy at elevated temperature would be a major benefit for manufacturing products with complex shapes. In the present study, hot deformation behavior of as-extruded Mg–6Zn–5Ca–3Ce alloy fabricated by RS was investigated by an isothermal compression test at a temperature (T) of 573–673 K and strain rate (ε˙) of 0.0001–0.01 s−1. Results indicated that the flow stress increases along with the declining temperature and the rising strain rate. The flow stress behavior was then depicted by the hyperbolic sine constitutive equation where the value of activation energy (Q) was calculated to be 186.3 kJ/mol. This issue is mainly attributed to the existence of fine grain and numerous second phases, such as Mg2Ca and Mg–Zn–Ce phase (T’ phase), acting as barriers to restrict dislocation motion effectively. Furthermore, strain compensation was introduced to incorporate the effect of plastic strain on material constants (α,Q,n,lnA) and the predicted flow stresses under various conditions were roughly consistent with the experimental results. Moreover, the processing maps based on the Murty criterion were constructed and visualized to find out the optimal deformation conditions during hot working. The preferential hot deformation windows were identified as follows: T = 590–640 K, ε˙ = 0.0001–0.0003 s−1 and T = 650–670 K, ε˙ = 0.0003–0.004 s−1 for the studied material.

Hot Deformation Behaviour and Constitutive Equation of Mg-9Gd-4Y-2Zn-0.5Zr Alloy

“…The slope of the curve at different strain rates was averaged, and the average value of the hot activation energy Q was obtained with Equation (8) as Q = 223.334 kJ·mol − 1 , which is higher than that of self-diffusion in pure Mg. Bao et al studied the hot deformation behaviour of Mg-6Zn-5Ca-3Ce (wt.%) alloy and believed that the change in the Q value was due to the exceptionally fine grain size, since these fine grains could act as barriers to effectively restrict dislocation motion [ 15 ].…”

“…Temperature of 603–633 K and strain rate of 0.03–0.005 s − 1 were projected to be the best process parameters using the constitutive equation and hot processing map. Bao et al constructed the processing map of Mg-6Zn-5Ca-3Ce (wt.%) alloy based on the Murty criterion [ 15 ]. According to the constitutive equation and hot processing map, the optimal parameters were T = 590–640 K, = 0.0001–0.0003 s − 1 and T = 650–670 K, = 0.0003–0.004 s − 1 .…”

Strain Modified Constitutive Equation and Processing Maps of High Quality 20MnCr5(SH) Gear Steel

“…in processing efficiency η. Therefore, Kumar et al [32,33] proposed the instability criterion based on DMM theory:…”