Abstract
The objects of investigation are ZK51A (ML12) alloy samples containing from 3.5 to 5.5 wt % Zn and 0.5–0.8 wt % Zr. The influence of Zn and Zr content on phase transition temperatures and the phase composition in equilibrium conditions and when using the Scheil–Gulliver solidification model is established using the calculation of phase diagrams in the Thermo-Calc program. It is shown that a significant increase in the liquidus temperature of the alloy occurs at a zirconium content in the alloy higher than 0.8–0.9 wt %, and an increase in the melting temperature above 800°C is required, which is undesirable when using steel crucibles. The equilibrium content of alloying components in the magnesium-based solid solution at various temperatures is calculated. The microstructure of as cast and heat-treated alloys with various concentrations of alloying components is investigated using scanning electron microscopy. The distribution of Zn and Zr in a dendritic cell of the as cast and heat-treated alloy is investigated. Zinc is concentrated along the dendritic cell boundaries in the as cast state, but its concentration in their center becomes higher than along the boundaries after heat treatment (HT). Zirconium is concentrated in the center of dendritic cells. It is shown that the two-stage solutionizing mode gives the largest increment of this characteristic: 330°C, 5 h + 400°C, 5 h. The influence of the aging temperature (150 and 200°C) on the sample hardness is investigated. It is revealed that it is higher in the case of aging at 200°C, and its maximum is observed under holding for 8‒10 h. The HT of the alloy, including solution treatment (330°C, 5h + 400°C, 5 h) with subsequent quenching and aging (200°C, 8 h), made it possible to attain an alloy ultimate strength of 285 ± 13.5 MPa and a elongation of 11.4 ± 1%.
Published Version
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