A New Constitutive Model for Thermal Deformation of Magnesium Alloys
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UCTION
MAGNESIUM (Mg) alloys have a series of advantages such as high specific strength and stiffness, superior damping performance and electromagnetic shielding characteristics, and can be potentially and widely used in automotive, aerospace, and electron industries.[1–4] Unfortunately, because of the hexagonal close-packed crystal structure with limited number of slip systems, Mg alloys have poor formability at room temperature.[5–7] Consequently, Mg alloys are usually formed at high temperatures. However, the narrow forming temperature range and high sensitivity to process parameters severely limit the further promotion of Mg alloys. With the help of FE simulation technology, the law of metal flow and the field distributions of strain, stress, and temperature at different deformation times can be predicted, which can provide theoretical guidelines for acquiring the optimal forming
JIAN ZENG, FENGHUA WANG, XIAOXIAO WEI, SHUAI DONG, ZHENYAN ZHANG, and JIE DONG are with the National Engineering Research Center of Light Alloy Net Forming and State Key Laboratory of Metal Matrix Composite, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, 200240, P.R. China. Contact e-mail: [email protected] Manuscript submitted June 29, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
parameters.[8–10] Nevertheless, the results of FE simulation can be really credible only when the accuracy of the input constitutive model is high enough.[11] Therefore, many scholars have done lots of work on developing a reasonable constitutive model for thermal deformation of Mg alloys. In the commercial brand Mg alloys, Zhou et al.[12] developed a new constitutive model of AZ61 alloy and obtained the optimized extrusion temperature and speed. Cai et al.[13] proposed a constitutive model of AZ41M alloy considering the compensation of strain. Tsao et al.[14] analyzed the effects of deformation temperature, strain rate, and strain on the flow stress of AZ61 alloy and developed a mathematical model as a function of temperature, strain rate, and strain using the amended Fields–Bachofen equation. Except for the commercial AZ61 and AZ41M alloys, the extensive attention also has been paid to constructing a constitutive model describing the deformation behavior of the other brand alloys, including AZ31,[15–17] AZ80,[18–20] AZ91,[21,22] and ZK60.[23] In the study on the constitutive model of rare-earth Mg alloy, Li and Zhang[24] investigated the hot deformation behavior of Mg-9Gd-4Y-0.6Zr alloy and constructed a plastic flow semi-empirical model for the relation between strain rate, strain, and temperature. Zhou et al.[25] used the improved Arrhenius-type equation to predict the flow behavior of the Mg-Gd-Y-Nb-Zr alloy. Using the new fitting method of Rieiro, Carsi, and
Ruano for direct calculation of the Garofalo constants, the deformation behavior of fine-grained extruded GWK940, GWK540, and GK50 alloys can be described by the Garofalo equation.[26] Additionally, Hao et al.[27] investigated the flow behavior of Mg-Zn-Y-Mn
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