Effect of annealing heat treatment on microstructure and hot deformation characteristics of extruded AZ61 magnesium alloy under hot compression

• Main Authors: Ching-hao Liao, 廖經皓
• Other Authors: Shyong Lee
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/38931620138110984808

博士 === 國立中央大學 === 機械工程學系 === 103 === In this study, the hot deformation characteristics and constitutive analysis of extruded AZ61 Mg alloy were investigated by hot compression tests conducted in the temperature range of 250 °C to 450 °C and strain rate range of 1×10−3 to 1 s−1 on a Gleeble-3500 thermo-simulation machine. The effect of strain on the constitutive parameters was taken into account in the constitutive analysis. Constitutive equations as a function of strain were established through a simple extension of the hyperbolic sine constitutive relation. The constitutive parameters, stress exponent n, activation energy Q, and ln A in the constitutive equations were calculated as a function of strain. Correlation between the strain-dependent constitutive parameters and flow behavior was analyzed. The constant stress multiplier (α) analysis result indicated that the calculated flow stresses were in good agreement with experimental ones, except at low strains at the deformation conditions with high strain hardening. On the other hand, the constitutive analysis with strain-dependent α value had better estimations between the calculated and experimental flow stresses throughout the entire temperature and strain rate ranges performed in this work. The effects of annealing heat treatments on the variations in constitutive parameters with strain were discussed. The hot ompressive flow curves exhibited typical features of dynamic recrystallization. Variations in constitutive parameters with strain were related to flow behavior and dependent on the initial conditions of the test specimens. The flow stresses of annealed AZ61 Mg alloys were predicted well by the strain-dependent constitutive equations of the hyperbolic sine function under the deformation conditions employed in this study.