Study on Dynamical Structure Change during Reversion in Aluminium Alloys

为了研究铝合金在还原过程中的动力学结构变化，进行了同步辐射-小角散射测量。现将本研究的主要结果总结如下：(1)根据还原温度的不同，结构变化可分为完全还原和部分还原两类。在完全回归的情况下，gp带体积分数的时间依赖性可以用Johnson-Mehl方程来描述。随着温度的升高，时间指数由0.5变为2.5。(2)当预时效试样在高于区域溶质温度下退火时，相变过程分为两个阶段。在第一阶段，区域尺寸没有减小，但区域内溶质浓度减小。下一阶段，区域大小逐渐减小直至消失。(3)当试样在低于区域溶质的温度下退火时，部分区域存活了下来，其中的体积分数可由共存曲线计算。(4)从室温开始以恒定升温速率加热预时效试样时，溶质浓度在较低温度下先下降，但区域大小没有变化。温度变得足够高，以至于这些区域根据平衡关系分解成基质。(5)为了解释上述实验数据，采用带移动边界的扩散方程进行了理论模型计算。(6)利用fcc Ising晶格，研究了还原过程。(7)综上所述，我们明确了回归过程的机制，区域分解为在区域边界处保持局部平衡的矩阵。(8)采用小角散射技术和原子探针场离子显微镜研究了A1-Zn和A1-Ag合金在析出过程中的结构变化。少

In order to study the dynamical structure change during reversion in aluminium alloys, the synchrotron radiation-small-angle scattering measurements have been preformed. The major results obtained in the present study are summarized as follows.(1) Depending on reversion temperatures, the structure changes have been classified into two categories as the complete reversion and the partial one. In the case of the complete reversion, the time-dependence of volume fraction of G.P. zones could be described in terms of Johnson-Mehl equation. Here the time exponent changed from 0.5 to 2.5 with increasing temperature.(2) When the pre-aged specimen was annealed at temperatures above the zone solvus, the reversion process followed by two satges. At the first stage, the zone size did not decrease, but the solute concentration inside zones decreased. In the next stage, the zone size decreased to vanish.(3) When the specimen was annealed at temperatures below the zone solvus, a part of zones survive … More d, of which the volume fraction could be calculated from the coexistence curve.(4) When the pre-aged specimen was heated-up from room temperature with a constant heating rate, the solute concentration decreased firstly at relatively lower temperatures, but the zone size did not change. Temperature became enoughly so high that the zones resolved into the matrix according to the equilibrium relationship.(5) In order to explain the above-mentioned experimental data, the theoretical model calculation using the diffusion equation with moving boundary has been performed.(6) By using the fcc Ising lattice, the reversion process has been investigated.(7) In conclusion, we made clear the mechanism of reversion process, by which the zones resolve into the matrix keeping the local equilibrium at the zone boundary.(8) The structural change during the precipitation process in A1-Zn and A1-Ag alloys has been also investigated by means of the small angle scattering technique as well as the atom-probe field ion microscopy. Less