• 한국주조공학회지
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• 제38권6호
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• pp.121-131
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• 2018

The effect of additives on the castability of the AC2BS aluminum alloy, which contains 35% recycled scrap, was investigated. For the wide utilization of the recycled scrap AC2BS aluminum alloy, the research results were compared to those with the AC2B virgin alloy, which is typical Al-Si-Cu alloy system. It was confirmed that the addition of Al-5%Ti-1%B increased the ${\alpha}$-Al nucleation temperature during solidification and decreased the grain size through cooling curve and microstructural observations of the recycled alloy. It was also found that an addition of Al-10%Sr decreased the eutectic Si growth temperature during the solidification process and modified the shape of the eutectic Si of the recycled alloy. The characteristics of fluidity, shrinkage and solidification crack strength were evaluated. For the AC2BS aluminum alloy containing 35% recycled scrap, both ${\alpha}$-Al grain refinement due to Ti-B and eutectic Si modifications due to Sr contributed to the improvement of the fluidity. The macro- shrinkage ratio increased with additions of both Al-10%Sr and Al-5%Ti-1%B and the micro-shrinkage ratio increased with the addition of Al-10%Sr but decreased with the addition of Al-5%Ti-1%B. The casting characteristics of TiB and Sr-treated AC2BS aluminum alloy containing 35% recycled scrap are similar to those of AC2B virgin alloy. The improvement of the solidification crack strength of the AC2BS aluminum alloy was possible by the reduction of the grain boundary the stress concentration through the enhancement by both ${\bullet}{\cdot}$-Al refinement and eutectic Si modification. More extensive use of the AC2BS aluminum alloy containing 35% recycled scrap can be expected in the future.

• 대한금속재료학회지
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• 제47권4호
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• pp.223-227
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• 2009

The precipitates, hardness, and tensile properties of Al-6.2Si-2.9Cu AC2B alloy were investigated with respect to solution treatment time at $500^{\circ}C$. $Al(Cu)-Al_2Cu$ eutectic, Si, ${\theta}-(Al_2Cu)$, and $Q-(Al_5Cu_2Mg_8Si_6)$ phases were observed in the as-cast specimen. With increasing the solution treatment time at $500^{\circ}C$, the $Al(Cu)-Al_2Cu$ eutectic and ${\theta}-(Al_2Cu)$ phases were gradually reduced and finally almost disappeared in 5 h. The mechanical properties, such as hardness, tensile strength, and elongation, were improved with solution treatment time until about 5 h due to the dissolution of the $Al_2Cu$ particles. With further holding time, the mechanical properties did not change much. The solution treated specimens for over 5 h at $500^{\circ}C$ exhibit almost the same tensile properties even after aging at $250^{\circ}C$ for 3.5 h. Accordingly, the optimal solution treatment condition of the Al-Si-Cu AC2B alloy is considered to be 5 h at $500^{\circ}C$.

• 한국주조공학회지
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• 제38권2호
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• pp.32-40
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• 2018

Changes in the microstructures and mechanical properties of an AC2B alloy through solution heat treatment were investigated using recycled AC2B cutting chips as raw material. The as-cast microstructure of the AC2B alloy comprised ${\alpha}$-Al, $Al_2Cu$, and coarse needle-shaped phases considered to be eutectic Si and an Al-Fe-Si based intermetallic compound. After solution heat treatments at $505^{\circ}C$ for 1 h and 6 h, the samples showed complete dissolution of $Al_2Cu$ and relatively fine distribution of intermetallic compounds. Hardness test results showed that the hardness rapidly increased after the solution heat treatment for 1 h by solid solution hardening, and the increase of hardness exhibited a plateau from 1 h to 6 h. The results of the hardness and tensile tests showed that there was no visible difference in the effect of 1 h and 6 h solid solution treatment.