THERMAL STABILITY OF CAST CONDUCTOR MICROALLOYED ALUMINUM ALLOYS

Abstract

The nucleation of the Al3X (X = Zr, Yb, Er, Hf) particles in the cast conductor Al alloys including the alloys additionally doped with Mg and Si was studied. The alloys were made by induction casting. To investigate the particle nucleation kinetics, the specific electrical resistivity (SER) and microhardness measurements were applied. It was shown that the investigated alloys can be subdivided into three groups. Group I includes the alloys, which the decrease in the SER with increasing annealing temperature takes place in due to the particle nucleation. Group II includes the alloys, which the particle nucleation takes place in during the bulk crystallization. The SER magnitude of such alloy was close to the SER of pure Al. The SER of the alloys of Group III almost doesn’t change during annealing and is 3.0-3.4 ·cm that evidences a high alloy solid solution stability. Using Jonhnson-Mehl-Avrami-Kolmogorov equation, the particle nucleation kinetics in the Group I alloys was analyzed. The activation energy of the particle nucleation in the Group I alloys was found to be close to the activation energy of volume diffusion, but the values of the decomposition intensity coefficient (n = 0.5-0.8) in Johnson-Mehl-Avrami-Kolmogorov equation appeared to be smaller that the theoretical value n = 1.5 typical for the particle nucleation inside the bulk crystal lattice. This contradiction was related to the presence of large primary or eutectic Al3X particles in the alloy structure. The Al-0.25%Zr-0.25%Er-0.15%Si alloy was shown to have the optimal set of properties: the characteristics of this alloy after annealing match the requirements to the alloys being developed: SER less than 2.95 ·cm, microhardness Hv ~ 550 MPa.