退火處理對AZ61鎂合金擠製件熱壓微結構變化及變形特性的影響

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

廖經皓(Ching-hao Liao)

指導教授 ： 李雄

國立中央大學/工學院/機械工程學系/博士(2015年)

摘要

本研究主要以Gleeble-3500金屬熱加工模擬測試機對AZ61鎂合金擠製材於變形溫度在250℃-450℃、應變速率：1 x 10-3 - 1 s-1進行熱壓縮實驗並探討其熱變形的機制。以組合方程式對其熱變形的機制進行研究，進而考慮應變對組合方程式的影響進行研究。本研究以雙曲線正弦函數律的組合方程式進行分析，且建立應變對各參數之間的變化；其中包含了應力指數n，活化能Q和材料常數ln A，進行應變對流變行為的相關性分析。在研究的過程中發現固定的應力乘積α，計算出來的流變應力與實驗值有良好的吻合率，但在低的應變的變形條件下出現了較高的應變硬化，使得應力高估的現象出現。然而在本研究組合方程式分析中加入應變對各參數變化可使計算和實驗的流變應力得到了一個更好的評估。
本研究也探討退火熱處理對組合方程式分析中加入應變對各參數間的變化。AZ61鎂合金經退火熱處理後，其熱壓縮的流變應力曲線呈現典型動態再結晶的特徵。然而不同的退火熱處理影響各試片的初始狀態，亦影響組合方程式中的各參數變化。

關鍵字

AZ61鎂合金 ； 組合方程式 ； 動態再結晶 ； 流變應力 ； 應力乘積 ； 應變相關的組合參數

並列摘要

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.

並列關鍵字

AZ61 Mg alloy ； Constitutive analysis ； Dynamic recrystallization ； Flow stress modeling ； Stress multiplier ； Strain-dependent constitutive parameters

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