Developing a high-strength Al-11Si alloy with improved ductility by combining ECAP and cryorolling

In this study, a high-strength Al-11Si alloy with an improved ductility was developed via a two-step processing route- equal-channel angular pressing (ECAP) and post-cryorolling. Specifically, the cast alloy was ECAP processed at 623 K for 16 passes, followed by multi-pass cryorolling with 50% thickness reduction. Herein, its mechanical properties was evaluated, and the underlying mechanisms for the improvement of both strength and ductility was investigated. Through systematic comparisons with other samples, including the cast, the castrolled, the ECAP-processed and the ECAP-annealed samples, we found the respective origin for the high strength and the improved ductility in the processed alloy. On the one hand, the high strength resulted from both grain boundary strengthening and dislocation strengthening caused by the thermo-mechanical processing. On the other hand, the improved ductility was primarily dictated by the uniform distribution of the very fine Si particles due to the attendant fragmentation of the Si phase during ECAP process. In addition, the results showed that the superior combination of strength and ductility could not be achieved by either processing step alone. This two-step processing route is also promising to benefit other Al-Si alloys for structural applications by optimizing their mechanical properties.