Manufacturing of High Strength, High Ductility, Rare Earth-Free Magnesium Alloy Plate and Sheet Materials by Differential Speed Rolling

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This award supports US manufacturing needs, industries and future workforce. With its lightness, strength, castability and damping capacity, magnesium alloys offer significant opportunities for lightweight applications in transportation, armor, biomedical and others. The use of magnesium alloys as lightweight structural materials is one of the most effective ways to overcome the challenges in energy conservation. Sheet metal is one of the most used forms of metal alloys in many industries such as automobile, aerospace, and consumer goods. Sheet metals are typically manufactured with rolling technology. However, due to the crystal structure of magnesium, sheet metals made with conventional rolling are brittle and low in strength for warm-to-room temperature forming thereby limiting their use. To unleash the potential of magnesium alloys, there is a need to improve their formability. This project meets this need through integrated alloy design and processing with focus on differential speed rolling in which the two rolls of a rolling mill run at different, predetermined speeds. This approach demonstrates a capability to produce magnesium plate and sheet with high strength and high ductility, and good formability. The research involves several disciplines including materials engineering and processing, mechanics of materials and advanced manufacturing. This convergent approach helps promote diversity and culture of inclusion as well as facilitates workforce development in manufacturing.Differential speed rolling (DSR) in which two rolls of a rolling mill run at distinct speeds can produce Mg alloy plates and sheets with textures dominated by basal plane orientations tilted in the rolling direction. This texture change leads to strong activation of basal slip and thus to higher fracture strains. DSR advances conventional rolling by providing additional controllable shear stresses which enhance dynamic precipitation and grain refinement via dynamic recrystallization leading to higher strength and ductility of Mg alloys. Compared to other thermomechanical processing technologies based on severe shear deformation, such as, equal channel angular extrusion and high-pressure torsion, DSR is scalable due to its continuous nature. However, there is a lack of understanding of the relationships between alloy composition, initial microstructure, rolling parameters, final microstructure (grain refinement, precipitates, texture) and thermomechanical properties of the processed alloys, and the appropriate rolling strategy for their warm-to-room-temperature formability. The team plans to perform experimental investigations driven by finite element simulations (FE-DEFORM) of plastic deformation in the rolling process. This research is expected to define the role of dynamic recrystallization, dynamic precipitation, twinning, texture evolution and grain growth in processing-microstructure-property relationships that lead to discovery of new approaches to improve formability and increase strain-hardening of Mg alloys.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.