Study on Dynamical Structure Change during Reversion in Aluminium Alloys

为了研究铝合金回复过程中的动态结构变化，进行了同步辐射小角散射测量。主要研究结果如下：(1)根据回复温度的不同，将结构变化分为完全回复和部分回复两类。在完全回复的情况下，G.P.带的体积分数随时间的变化可以用Johnson-Mehl方程来描述。随着温度的升高，时间指数从0.5变化到2.5。(2)当预时效样品在Solvus区以上温度下进行退火时，回复过程经历了两个阶段。在第一阶段，区域尺寸没有减小，但区域内的溶质浓度降低。在下一阶段，区域尺寸减小到消失。(3)当样品在低于区域Solvus的温度下进行退火时，部分区域存活…当预时效样品在恒定升温速率下从室温升温时，溶质浓度在相对较低的温度下首先降低，但区域大小没有变化。(5)为了解释上述实验数据，用带移动边界的扩散方程进行了理论模型计算。(6)利用面心立方伊辛晶格研究了反转过程。(7)阐明了反转过程的机理。用小角散射技术和原子探针场离子显微镜研究了Al-Zn和Al-Ag合金在析出过程中的结构变化。较少

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