Instantaneous efficient microstructure manipulation of eutectic Al-Si alloy by trace in-situ nanoparticles and their mechanism in superior tensile properties

The overall microstructure-manipulated Al-13Si-5Cu-0.6 Mg alloy was successfully fabricated via introducing 0.1 wt% Zr55Cu30Al10Ni5 amorphous alloy manipulator with short time of 60 s, to determine its suitability for applications at room and higher temperatures. The microstructure manipulation mechanism, mechanical properties and strengthening mechanism in manipulated Al-13Si-5Cu-0.6 Mg alloy were discussed. The Zr55Cu30Al10Ni5 amorphous alloy manipulator provides more nucleation sites in the formation of primary Si, Al-Si eutectic and Al2Cu. As a result, the optimal microstructure is composed of finer alpha-Al grains, Al2Cu and more rounded primary and eutectic Si, with sizes decreased to similar to 52%, 13%, 73% and 42%, respectively. The yield strength, tensile strength, elongation and fracture strain of manipulated Al-13Si-5Cu-0.6 Mg alloy are improved by 22.9%, 16.8%, 58.2% and 47.7% at room temperature than those of the unmanipulated Al-13Si5Cu-0.6 Mg alloy, respectively. The improved tensile properties at room temperature are attributed to the significant strengthening effect of smaller precipitates and grain refinement while the excellent plasticity is derived from finer alpha-Al grain, round-corner primary Si and eutectic Si spheroidization. The yield strength and tensile strength are increased by 28.1% and 15.3% at 250 degrees C, and 28.3% and 10.8% at 300 degrees C, respectively. The strengthening mechanism at high temperature is mainly the second phase strengthening and the effect of finer eutectic Si on the pinning grain boundary. The overall microstructure manipulation in this work provides better comprehensive mechanical properties and a practicable method to fabricate the Al-Si-Cu-Mg alloy with superior strength and ductility, especially for die-casting alloy with short-time and high-efficiency.