Zr Microalloying and Microstructure Construction of Al-Y Heat-Resistant Alloy and Its Strengthening and Toughening Mechanisms

Abstract

This study optimizes the strength, plasticity, and heat resistance of Al–Y–Zr ternary alloys through Zr microalloying and the engineering of a heterogeneous grain structure. Based on thermodynamic calculations, several Al–5Y–xZr alloys (x = 0, 0.25, 0.5, and 1.0 wt.%) were fabricated via casting, cold rolling, and annealing. The results demonstrate that the average grain size of as-cast Al–5Y–xZr alloys decreased significantly from 605.45 µm to 164.22 µm as the Zr content increased from 0 to 0.5 wt.%. After multi-pass rolling and annealing at 280 °C for 1 h, the Al–5Y–0.5Zr alloy developed a heterogeneous microstructure comprising fibrous primary α-Al and ultrafine eutectic phases. This treatment simultaneously enhanced both strength and ductility compared to the as-rolled state. Compared with the binary Al–5Y alloy, the Zr-microalloyed sheets exhibited remarkable softening resistance, retaining a tensile strength of 194.75 MPa (98.93% strength retention) after annealing. Moreover, annealing at 280 °C for 1 h significantly reduced the dislocation density in the Al matrix while enhancing the strain-hardening capacity of the Al grains and the load-bearing capability of the β-Al₃Y phases. The dual deformation mechanisms of the β-Al₃Y phases (twinning and dislocation slip) and the formation of a heterogeneous structure—comprising soft primary α-Al domains and hard β-Al₃Y domains—are identified as the primary contributors to the alloy’s exceptional strength–toughness synergy.