A Fundamental Study of Flow Mechanisms in Nanostructured Al Alloys and Intermetallic Compounds

Oregon State University, Corvallis OR

Investigators

Abstract

Non-technical Abstract: The production of lightweight aluminum (Al) having high strength but sufficiently deformable without breaking under stress is technically challenging in manufacturing to accelerate their applications to automotive and aerospace industries. Early studies demonstrated that significant microstructural refinement through severe permanent deformation by a combination of high-pressure and twisting (torsion) leads to excellent hardness in bulk metals. Thus, the objective of this project is to scientifically investigate how to achieve high strength and good elongations to failure in conventional Al alloys and intermetallic compounds after the microstructural refinement process. The importance of this project is to understand the strengthening and flow mechanisms of the nanostructured Al systems after the high-pressure and torsion processing, and to determine how to overcome the paradox of strength and formability in bulk nanostructured Al alloys and its compounds. These results are expected to have an important positive impact because a mechanistic understanding of improving the mechanical properties in bulk metals will provide new opportunities for the development of strategies for the applications of Al alloys and lightweight engineering materials selections. The research requires proficiency in a variety of areas including physics, materials science, and mechanical engineering, making it challenging and rewarding for graduate and undergraduate students who will be supported by this program. Technical Abstract: Achieving both high strength and good ductility is currently not controllable in Al alloys and intermetallic compounds. Although grain refinement by high-pressure torsion (HPT) generally improves the hardness of metals, the strategies for achieving both high strength and ductility in metallic materials are available only under limited conditions: in precipitation-hardened alloys or in materials containing high densities of nano-twins. Except in age-hardenable compositions, it is a major challenge to introduce those into Al systems having high stacking fault energy. Thus, objectives of this project are to understand the plastic flow mechanisms for strengthening and plasticity in micro- and macro-scales in ultrafine microstructures, and to design strategies to increase both strength and ductility of ultrafine-grained Al systems processed by HPT. This project combines expertise in metallurgical research on nanocrystalline materials with advanced characterization methods of measurements by the novel nanoindentation technique and state-of-the-art X-ray and electron diffraction analysis. These techniques allow to identify the complex metal flow with concurrent texture changes in a time scale under ambient and elevated temperatures. The contribution of this project is significant because the acquired scientific knowledge of improving mechanical properties of bulk metals can be extended to a wide range of polycrystalline materials, which is expected to expand our current engineering materials selections and produce an increased U.S. competitiveness in advanced manufacturing. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.