NZ30K镁合金时效析出动力学与强化模型的研究

PRECIPITATION KINETICS AND YIELD STRENGTH MODEL FOR NZ30K-Mg ALLOY

利用等转变量方法和恒速升温时效过程中的电阻实验研究了NZ30K镁合金的析出动力学，获得了动力学模型的激活能Ear和修正指前因子Aar，可用于准确描述不同时效条件下强化相的析出过程．NZ30K镁合金欠时效阶段和峰时效的力学性能显示，在180～250℃范围内峰时效屈服强度一致，约为150MPa．通过最小二乘法确定了NZ30K镁合金180-250℃范围内时效时析出强化模型参数C，约为93MPa，实验数据和模型预测数据一致，证明该模型能应用于NZ30K镁合金欠时效和峰时效条件下屈服强度的预测．

Age-hardening effect is considerably strong in magnesium alloys containing Nd, making it possible to develop magnesium alloys with low cost and high strength. Although there have been massive researches about the precipitation product sequence and strengthening models in magnesium, aluminum and other light alloys during their ageing processes, those of NZ30K-Mg alloy, a newly-developed magnesium alloy, has not been carefully investigated. The present work mainly focuses on the model of precipitation kinetics and strengthening of NZ30K-Mg alloy. The precipitation kinetics has been investigated using electrical resistivity testing during continuous heating with different heating rates and formulated based on the isoconversional method. Two related model parameters, modified pre-exponential factor A＇o and activation energy Ear were respectively determined. The precipitation behavior of NZ30K-Mg alloy during ageing processes can also be intrinsically explained from the variations of Eo and In Aar with the precipitation fraction. This kinetics model with two above-mentioned parameters can accurately describe the precipitation of strengthening phase during different ageing processes. The yield strength of under-aged and peak-aged NZ30K-Mg alloy have been tested and the results show that the testing samples isothermally aged at different temperature from 180 to 250 ℃ have almost the same peak yield strength of about 150 MPa, indicating that the strengthening effect of under-aged and peak-aged NZ30K-Mg alloy is only determined by the precipitation fraction within a certain range of temperatures. The precipitation strengthening model of NZ30K- Mg alloy has been carefully derived, and the parameter C in the model has then been determined by least squares method based on the tested yield strength data. The value of C is about 93 MPa. The prediction of yield strength of under-aged and peak-aged NZ30K-Mg alloy has been performed and fit well with the tested ones, demonstrating the effectiveness of precipitation strengthening model and its engineering application prospects.