Cast aluminum alloys of the A356 have widespread applications due to their excellent castability, corrosion resistance, and good mechanical properties in the heat-treated condition, especially in the automotive and aircraft industries. Increasing demands on such material and high cost of raw material naturally have induced to use secondary aluminum alloys. However with using secondary aluminum showing problems is in reduced mechanical properties. Therefore this studies focus on recycling secondary aluminum alloy to drop cost of production, besides to acquire the effect of protection of environment.
According to the investigation of Nam et al., it has been reported that the Mn-precipitates in AA6067 alloy play the major role in increasing the strength without sacrificing ductility, improve fatigue life of low cycle and high cycle fatigue, enhance the fracture toughness and increase corrosion resistance. In addition Mn is often added as alloying elements to increase the strength and hardenability because the β-AlFeSi which is very hard and brittle, and have relatively low bond strength with the matrix has been found to crystallize in the Chinese script rather than needlelike morphology due to Mn addition.
When Mn is added to A356 alloy to 0.4.wt.%, the alloy has a good tensile properties, compared with typical and virgin A356 cast alloy. After micro structure analysis of the A356-0.4wt.% alloy, the effects of neutralizing β-AlFeSi phase and formation of α-precipitation in Al rich phase have resulted in enhancing tensile properties.
Moreover like as Mn to A356 alloy, Cr is also added with the same methods. As a result β-AlFeSi solidified by granular, not needle, and elongation is much higher than Mn containing alloys, however tensile strength a little bit lower.
뛰어난 주조성과 내침식성 및 좋은 기계적 성질을 가진 A356 합금은 현재 폭 넓게 사용되고 있다. 수요가 계속적으로 증가하고 생산 단가의 상승 및 원자재값 상승등의 요인으로 재활용 A356 합금의 수요도 함께 증가하는 추세이다.따라서 본 연구에서는 A356합금의 재활용시 나타나는 기계적 특성의 감소 원인을 찾아내고 이에 따르는 해결책을 연구해 보았다.특별히 조직내에 Mn이나 Cr등의 전이 금속 원소를 첨가함여 정출 침상을 제어하고 석출상을 생성시켜 기계적특성의 변화를 관찰하였다.
