Summary
Commercialization of the casting processes utilizing the technology of SSM processing, specifically, rheocasting of Al alloys has been tedious for the past three decades due to the complexity of the process, high level of exter- nal artifacts such as oxides and dissolved hydrogen. We believe that CDS is a viable and low cost process alterna- tive to obtain shaped castings of Al alloys with a non- dendritic morphology of the primary Al phase, especially the Al wrought alloys. However, this study is only a feasi- bility study to test if the proposed mechanism of the CDS process is transferable to an industrial scenario and does not attempt to optimize all the various complex interact- ing parameters influencing the final casting quality. The study demonstrated the castability of the alloy made from CDS resulting in a casting with reasonable soundness and integrity. In this study, a procedure has been formulated to design and optimize the critical parameters in the CDS process such as the alloy compositions and melt tem- peratures of the two pre-cursor alloys. These parameters
have been successfully optimized for Al wrought Alloys 2024, 6082 and 7075. Shape cast components of Alloys 2024, 6082 and 7075 by CDS and tilt-pour casting pro- cess showed reasonable levels of integrity, no discernable hot-tearing phenomenon and no visual and unusual cast- ing defects. Attempts to shape cast these alloys by con- ventional means using a superheated melt failed and did not yield a casting with any level of integrity. The study clearly demonstrates that further research to optimize the CDS process for a commercial casting operation is es- sential to explore shape casting of various Al wrought alloys. An automated device for mixing would have to be designed to eliminate mixing of the alloy through a direct top pouring; and to achieve precise control over the mass ratio and to obtain a cleaner mixing process with minimum melt breakdown and oxide/dissolved hydrogen inclusions. It is worth mentioning that all Al wrought al- loys may not be amenable to the CDS process and the precursor alloys with very low levels of Fe in them would not be economically feasible. Alloys with minor devia- tions from the respective Al wrought alloy compositions
Table 10. CDS Process Alloy Compositions of 7075 Al Wrought Alloy with Three Different Recycling Schemes for Foundry Returns
International Journal of Metalcasting/Spring 11
61
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