Subgrain growth in presence of nanosized dispersoids in Al–4·5Zn–1Mg alloy

Abstract

In this paper, an analytical model for subgrain growth in the presence of nanosized dispersoids is presented. The growth rate of subgrains is correlated to the mobility of low angle grain boundaries (LAGBs) and the net driving force for growth. The driving force is considered as the difference between stored energy, being inversely proportional to the average subgrain size, and the Zener drag pressure. A material dependent constant necessary for the determination of the mobility of LAGBs is estimated by fitting the model predictions into the experimental results. Model predictions of the evolution of subgrain sizes with annealing time at different temperatures show that subgrain growth intensifies with increasing annealing temperature. The magnitude of the Zener drag pressure has a predefined effect on the subgrain growth rate. The model predicts that when the P_Z/γ_s ratio is smaller than 1 μm⁻¹, the Zener drag pressure has an effect on subgrain size and the subgrain growth rate tends to decrease. However, when the P_Z/γ_s ratio is larger than 1 μm⁻¹, there is a limit beyond which the subgrain size does not increase with increasing annealing time. The limiting subgrain size is a function of the surface boundary energy and Zener drag pressure.

Keywords:

• Subgrain
• Growth
• Dispersoids
• Aluminium

This research was carried out under the project number MC 4·04203 in the framework of the Research Program of the Materials innovation institute M2i (www.m2i.nl). The authors acknowledge Mr K. Kwakernaak and Mr E. R. Peekstok for assistance in microstructure examinations.