Effect of Grain Refiner and Eutectic Si Modifier on Casting Properties of Al-Si-Cu Alloy System Containing Recycled Scrap

재활용 스크랩 함유 Al-Si-Cu계 합금의 주조특성에 미치는 결정립 미세화제와 공정 Si 개량화제의 영향

Abstract

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.

Fig. 1. Schematic drawing of thermal analysis test mold.

Fig. 2. Schematic drawing of fluidity test mold.

Fig. 3. Schematic drawing of (a) Shrinkage test mold and (b) Method for shrinkage measurement.

Fig. 4. Schematic drawing of solidification-cracking test equipment.

Fig. 5. Change of cooling curve with addition of Ti-B and Sr additives.

Fig. 6. Microstructure (a) and SEM/EDS results (b) of AC2BS alloys.

Fig. 7. Effect of additive addition on the microstructure of AC2BS alloy.

Fig. 8. Results of fluidity test with addition of scrap, Sr and TiB-Sr additives.

Fig. 9. Results of fluidity length with addition of scrap, Sr and TiB-Sr additives.

Fig. 10. Sectional views of shrinkage test specimens.

Fig. 11. Results of shrinkage measurement with addition of scrap, Sr and TiB-Sr additives.

Fig. 12. Results of hot tearing strength-elongation curves with addition of scrap, Sr and TiB-Sr additives.

Fig. 13. Results of solidification crack strength with addition of scrap, Sr and TiB-Sr additives.

Table 1. Chemical composition of AC2B and AC2BS alloy (wt.%).

Table 2. Conditions for melting and melt treatment.

Table 3. Experiment conditions for solidification-cracking test.

Table 4. Comparison of primary nucleation temperature and eutectic nucleation temperature with addition of TiB and Sr additives.

Table 5. Comparison of α grain size and aspect ratio of eutectic Si.