Influence of a Silicon Additive on Resistivity and Hardness of the Al–1% Fe–0.3% Zr Alloy

Аннотация

Isothermal sections of the diagram of the Al–Fe–Si–Zr alloy at temperatures of 450 and 600°C, as well as polythermal sections at concentrations of silicon up to 2 wt % and zirconium up to 1 wt %, are analyzed using computational methods with the help of Thermo-Calc software. It is shown that the favorable phase composition consisting of the aluminum solid solution (Al), the Al₈Fe₂Si phase, and Zr (which completely enters the composition of the solid solution (Al) during the formation of the cast billet) can be attained in equilibrium conditions at silicon concentrations of 0.27–0.47 wt %. To implement the above-listed structural components in nonequilibrium conditions and ensure that Zr enters the (Al) composition, experimental ingots were fabricated at an elevated cooling rate (higher than 10 K/s). A metallographic analysis of the cast structure of experimental samples revealed the desired structure with contents of 0.25 wt % Si and 0.3 wt % Zr in the alloy. The microstructure of the Al–1% Fe–0.3% Zr–0.5% Si alloy also contains the eutectic (Al) + Al₈Fe₂Si; however, the Al₈Fe₂Si phase partially transforms into Al₃Fe. The structure of the alloy with 0.25 wt % Si in the annealing state at 600°C contains fragmented particles of the degenerate eutectic (Al) + Al₈Fe₂Si along the boundaries of dendritic cells. It is established that the Si: Fe = 1: 2 ratio in the alloy positively affects its mechanical properties, especially hardness, without substantially lowering the specific conductivity during annealing, which is explained by the formation of the particles of the Al₈Fe₂Si phase of the compact morphology in the structure. Moreover, silicon accelerates the decay of the solid solution by zirconium, which is evidenced by the experimental plots of the dependence of hardness and resistivity on the annealing step. The best complex of properties was shown by the Al–1% Fe–0.3% Zr–0.25% Si alloy in the annealing stage at 450°C with the help of the optimization function at specified values of hardness and resistivity.