Precipitation kinetics of 2519A aluminum alloy based on aging curves and DSC analysis

The precipitation kinetics of 2519 A aluminum alloy after different cold rolling reductions before aging was investigated by hardness test and differential scanning calorimetry（DSC）. The activation energy was calculated according to DSC curves using single heating rate method. The microstructures of as-rolled and peak-aged alloys were observed by transmission electron microscopy（TEM）. The result shows that the age hardenability reduces and the activation energy rises with increasing the reduction from 7% to 40%. Nonuniform dislocations are found in as-rolled alloy and inhomogeneous distribution of θ′ phase is revealed in peak-aged alloy when the reduction is 15%. The inhomogeneous distribution of θ′ phase may be related to the age hardenability reducing and activation energy rising.

Precipitation kinetics of GP zones,metastable η′ phase and equilibrium η phase in Al-5.46wt.%Zn-1.67wt.%Mg alloy

Thermal analysis is one of the most used techniques for analyzing the behavior of aluminum alloys in order to analyze the precipitation of Guinier-Preston(GP)zones and different phases formed.In the present work,the behavior of the Al-5.46wt.%Zn-1.67wt.%Mg alloy was studied.The mechanism and kinetics of precipitation of the GP,the metastable phaseη′and the equilibrium phaseηwere investigated using DSC carried out between room temperature and 480℃at heating rates of 5,10,15 and 20℃/min.The apparent activation energies,calculated by DSC from isothermal calculation method using JMAK model,for GP,η′andηwere 56,79 and 96 kJ/mol,respectively,and those calculated by non-isothermal calculation method using Kissinger methods were 57,82 and 99 kJ/mol,respectively.The values of Avrami parameter,n,from isothermal calculation,during the precipitation of the GP,η′andηwere 1.103,1.9075 and 1.92,respectively,and those calculated by non-isothermal were 0.86,2.30 and 2.24,respectively.The results show that GP zones formation is governed by the migration of Zn and Mg atoms while the precipitation of theη′metastable phase and theηstable phase is governed by both the migration and the diffusion of the solute atoms.

In situ differential scanning calorimetry analysis of dissolution and precipitation kinetics in Mg-Y-RE alloy WE43

Further development of our differential scanning calorimetry(DSC)method for the analysis of solid-solid phase transformations now also allows for its application in the kinetic analysis of age hardening in Mg alloys.As a result,the state-of-the-art for DSC on Mg alloys has been improved with respect to the accessible temperature range,zero-level accuracy and dynamic range.DSC analysis was performed on the example of Mg wrought alloy WE43.Heating DSC experiments on the initial condition T4 and even direct continuous cooling DSC analysis on the kinetics of quench induced precipitation during cooling from solution treatment were possible,covering a dynamic range of 0.01-3 K/s.The DSC findings are discussed with respect to literature knowledge and scanning electron microscopy analysis of the defined heat treatment states.

Particles Morphology and Forming Analysis of Al-Si-Cu-Mg Alloys

The study aims at observation of precipitation distribution micrograph and analysis of forming kinetics mechanism of microstructure particles of Al-Si-Cu-Mg alloys. The microstructure morphology of some particles such as primary silicon and precipitates from the matrix of Al-Si-Cu-Mg alloys is observed by OM,SEM and EDS. The primary silicon forming kinetics is analyzed by EBSD. Twin plane re-entrant edge growth mode results in the blocky or diamonded TRD morphology formation. The precipitates of Q-Al5Cu2Mg8Si6,θ-Al2Cu,β-Al5FeSi and ε-Mg2Si are characterized by EDS and they are distributed in the eutectic region. The forming kinetics of them is analyzed by DSC. Six peaks are present in particles formation in different temperature ranges.The particles forming are determined by the analysis of the DSC traces during heating and cooling of Al-Si-CuMg alloys.

Al-Mg-Si-(Cu)铝合金在连续升温中的析出行为

采用差示扫描量热法(DSC)研究了Al-Mg-Si和Al-Mg-Si-Cu铝合金的连续升温时效析出行为,并结合JMA方程分析Cu对该合金时效析出动力学的影响,计算出各种亚稳相析出动力学参数,进而得出各相析出的相关动力学表达式及TTT曲线。结果表明:Cu显著地提高了Al-Mg-Si合金的时效硬化效果和速率,这与Cu的添加降低了析出激活能密切相关;Al-Mg-Si合金原子团簇、GP区、β〞和β'的激活能分别为(67.3±1.5)、(96.9±3.5)、(106.6±3.1)和(158.9±3.9)kJ/mol;而Al-Mg-Si-Cu铝合金原子团簇、GP区、β〞、β'、Q'和Q相的激活能分别为(62.0±1.8)、(87.8±3.2)、(97.7±3.1)、(137.0±4.2)、(125.5±4.3)和(266.7±5.4)kJ/mol。

热轧板退火温度对6×××系铝合金β″相析出动力学的影响

采用差示扫描量热法(DSC)研究热轧板退火温度对6×××系铝合金时效过程中β″相析出动力学的影响。计算热轧板在不同退火温度下β″相形成激活能,并对不同热轧板退火温度的试样模拟烤漆后进行力学性能实验。结果表明:随着热轧板退火温度的提高,β″相的形成激活能略微降低,表明在时效过程中β″相更容易形成,合金的模拟烤漆强度因此得到提高。热轧板退火温度的提高,增大了基体中的Mg、Si原子的过饱和度,即增大了时效过程中β″相的形成驱动力,从而提高合金的模拟烤漆强度。

NiTi形状记忆合金中共格Ni_4Ti_3沉淀相生长动力学行为的相场法模拟

采用基于扩散场理论的宏观相场模型对NiTi形状记忆合金中具有菱方结构的共格Ni_4Ti_3相的析出及长大过程进行了模拟研究;沉淀相的形貌演化通过求解非守恒参量场Ginzburg-Landau控制方程和守恒浓度场Cahn-Hilliard扩散方程获得。与二维模型相比,本研究采用了准确的晶体学参数及改进的数学模型,获得了更为直观及合理的三维盘状变体及二维透镜状变体;Ni_4Ti_3沉淀相的长度、宽度和面积分数随时间的变化分别遵循指数、线性和对数关系;且其长度与宽度的比值并非恒定值,在生长初期该比值有较大的增速而随后逐渐减慢,能很好地解释沉淀相盘状及透镜状形貌特征形成的原因并与相关实验结果吻合。