An object of this study is the improvement of mechanical properties, especially tensile properties of secondary A356 alloy as much as Virgin A356 alloy. Secondary A356 alloy, which contains 0.2wt.%Fe was prepared as a base alloy for experiment. And the variation of microstructure, solidification sequence and precipitation phenomena in response to Mn and Cr additions were observed. The effects of Mn and Cr on the mechanical properties were also examined and the specific Mn and Cr composition that increases ductility and strength simultaneously was investigated. Mechanical properties of tested alloys were compared with A356 virgin and secondary alloy.
Mn and Cr change solidification sequence of alloy, and modify a morphology of Fe-bearing intermetallics. The morphology of Cr containing intermetallics refined favorably than Mn intermetallics. Mn induces disorder-order transition of crystallized phases. The additional Mn or Cr bearing dispersoids precipitate at high temperature. Mn and Cr contribute to Mechanical properties of alloy in deferent way.
Consequently, a alloy composition for a recycle process of secondary alloy, has been proposed as A356-0.2wt.%Fe-0.13wt.%Mn/0.13wt.%Cr and it shows high strength and ductility. Its mechanical properties were better than A356 virgin alloy, and remarkably improved compare to A356 secondary alloy.
A356 secondary합금의 기계적 성질을 향상시키는 것에 초점을 맞추어 Mn과 Cr을 첨가하면서 A356합금의 미세구조와 기계적 성질에 미치는 영향을 조사하였다. Mn과 Cr은 A356합금의 정출상과 석출상의 형성과 형상에 영향을 미쳤으며, A356 secondary합금에서 주로 나타나는 침상의 Fe관련 상의 생성을 방해하고, 새로운 석출상을 형성하였다. 이러한 Mn과 Cr의 영향은 합금의 미세조직을 개선하고 그 결과 기계적특성(인장특성)이 향상되는 결과로 나타났다. Mn과 Cr의 영향을 종합하여 secondary 합금의 기계적 성질을 개선할 수 있는 최적 조성을 설정하였으며, 이러한 합금조성을 활용할 경우 제품생산과정에서 상당한 생산원가 절감효과를 누릴수 있을 것으로 보인다.
