Improvement in tensile ductility and aging response of high-speed-extruded Mg-5Bi-3Al alloy via trace Zn addition

초록

This study examines the effects of trace Zn addition on the microstructure, tensile properties, and precipitation behavior of a high-speed-extruded Mg-5Bi-3Al (BA53, wt.%) alloy. While this alloy exhibits excellent extrudability and high strength, its low ductility and prolonged aging time to achieve peak hardness limit its commercial viability. To address these limitations, 0.5 wt.% Zn was added to the BA53 alloy to enhance its ductility and reduce its peak-aging time without compromising its strength. Subsequently, BA53 and Mg-5Bi-3Al-0.5Zn (BAZ530) alloys were extruded at 400 degrees C with a die-exit speed of 40 m/min. Microstructural analysis revealed that trace Zn addition had minimal impact on grain size or Mg3Bi2 particle distribution but reduced the maximum texture intensity of the high-speed-extruded alloy. The BAZ530 alloy demonstrated a 38% increase in tensile elongation compared to the BA53 alloy, with no reduction in tensile yield strength, primarily due to the activation of non-basal slip systems. In addition to improving ductility, Zn addition significantly reduced the peak-aging time at 180 degrees C from 128 h for the BA53 alloy to 16 h for the BAZ530 alloy, an eightfold decrease, while achieving comparable peak hardness values. This acceleration is attributed to the substitution of Bi atoms by Zn atoms in the Mg3Bi2 phase, which lowered the formation enthalpy and increased nucleation rates. Overall, our findings demonstrate that trace Zn addition effectively enhances tensile elongation and accelerates precipitation in high-alloyed Mg-Bi-Al alloys.

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