Investigation on recrystallization behavior of Al-Zr alloys by means of internal friction measurement

Abstract

Recrystallization of cold-worked Al-Zr alloys containing 0.03 to 0.33wt%. of Zr was investigated by internal friction measurement with an inverted torsional pendulum apparatus. Two typical heat treatments were carried out before final cold working. In one type of the treatment (solution treatment), specimens were water-quenched after annealing at 640°C for 24 hours and in the other (precipitation treatment), specimens were aged at 250°C for 300 hours after water-quenching from 640°C. The results obtained are as follows:(1) An internal friction peak which was related with recovery and recrystallization appeared in the temperature range between 250°C and 400°C. The peak temperature was proportional to the logarithm of Zr concentration. This peak temperature was identified as a measure of the temperature at which recrystallization was completed, because the recrystallization temperature of Al-Zr alloys determined by hardness measurement peak proportional to the peak temperature of the internal friction and also to the logarithm of Zr contents. The was temperature was found to attain to 400°C.(2) There was no significant difference of the peak temperature between the solution treated and the precipitation treated specimens when Zr concentration was identical. However, the peak temperature of the solution treated specimens was slightly higher than that of the precipitation treated specimens.(3) It was concluded that the heat resistance mechanism of Al-Zr alloys was attributed largely to the presence of Zr as a solute in the supersaturated solid solation below 400°C. Diffusivity of volume diffusion of Zr in Al is extremely smaller than that of self-diffusion of Al. Thus, the solute Zr had a pinning effect on motion of dislocations and migration of grain and subgrain boundaries during annealing, and consequently thermal stability of cold worked structure was increased.