A Study of Thermal Stability of Cast Electroconductive Microalloyed Aluminum Alloys

The processes of precipitation of particles of Al3X (X = Zr, Yb, Er, Hf) in cast conductive aluminum alloys have been studied, including those alloyed with Mg and Si. The alloys have been produced using the induction casting technique. To study the precipitation kinetics of particles, methods for measuring specific electrical resistivity (SER) and microhardness have been used. It has been shown that the studied alloys can be divided into three groups. Group I contains the alloys in which an increase in the annealing temperature results in a decreases in SER due to the precipitation of particles. Group II contains the alloys in which the precipitation of particles occurs during the crystallization of an ingot. The SER value of these alloys is close to that of aluminum. The SER value of the alloys of Group III remains almost constant upon annealing and is 3.0–3.4 μΩ cm, which indicates the high stability of the solid solution. The Johnson–Mehl–Avrami–Kolmogorov equation is used to study the precipitation kinetics of particles in alloys of Group I. It has been established that the activation energy of the precipitation of particles in alloys of Group I is close to the activation energy of bulk diffusion, while the values of the decomposition rate coefficient (n = 0.5–0.8) in the Johnson–Mehl–Avrami–Kolmogorov equation are lower than the theoretical value n = 1.5 typical of the precipitation of particles in the bulk of grains. The observed contradiction is associated with the presence of large primary or eutectic Al3X particles in the structure of alloys. It has been shown that the Al–0.25% Zr–0.25% Er–0.15% Si alloy exhibits an appropriate set of properties; after annealing their characteristics meet the requirements for the designed alloys: SER is less than 2.95 μΩ cm and the microhardness is ~550 MPa.