Mechanical Behavior and Deformation Kinetics of Aluminum Alloys Processed through Cryorolling and Subsequent Annealing KANDARP CHANGELA, HARIHARAN KRISHNASWAMY, and RAVI KUMAR DIGAVALLI The influence of cryorolling (CYR) on the microstructure, mechanical properties, and formability of heat-treatable (AA 6061) and non heat-treatable (AA 5083) aluminum alloys was investigated. Solutionized (SL) AA 5083 and AA 6061 alloy plates are cryorolled to reduce the thickness from 6.5 to 1 mm (the total true strain of 1.87). Short annealing treatment is performed on cryorolled samples at different temperatures with a fixed annealing time to improve ductility. The effect of annealing temperature on microstructure, mechanical properties, and formability was systemically studied. The results showed grain refinement after CYR with higher dislocation density when compared to the SL condition, and their effect is reflected in the mechanical properties. The limiting dome height test is used in the present work to compare the formability of cryorolled and annealed samples. The formability characteristics correlated well with the strain hardening behavior, which is modeled using the Kocks–Meck- ing–Estrin (KME) dislocation density model. The dislocation density evolution in the original KME model was modified to consider the contributions of grain size, solutes, and precipitates. The tensile curves predicted from the KME model correlated well with the experimental curves in all the conditions investigated. In addition to that, the predicted dislocation density using the modified KME model agreed well with the dislocation density determined experimentally. https://doi.org/10.1007/s11661-019-05532-2 Ó The Minerals, Metals & Materials Society and ASM International 2019 I. INTRODUCTION SEVERE plastic deformation (SPD) is used to produce high-strength metallic materials by severe grain refinement. [1] The grain refinement is primarily due to the dislocation accumulation leading to the formation of high-angle grain boundaries (HAGBs). One of the methods to augment the dislocation multiplication is to suppress the dynamic recovery by lowering the deformation temperature to cryogenic levels. [2] This method is especially suitable for aluminum alloys with high recovery due to increased stacking fault energy (SFE). Significant past research has been conducted on different Al alloys to obtain high-strength materials through various deformation techniques at a cryogenic temperature such as cryorolling (CYR), [3] asymmetric CYR, [4] cryo-ECAP, [5] and cryoforging. [6] Among these, CYR constitutes an interesting thermomechanical pro- cessing route for sheet metal application, which induces significant microstructural refinement and enhances mechanical strength. [7] In 2002, Wang et al. [8] initially performed CYR of pure copper and obtained a high-strength ultra- fine-grained (UFG) structure with sufficient ductility. It is well known that high dislocation density structure plays a major role in refining the microstructure during CYR. [9] However, the as-cryorolled alloys exhibit poor ductility at room temperature, which limits their indus- trial applications. The ductility, however, can be improved to a great extent by subsequent low-temper- ature annealing treatment without sacrificing the max- imum strength obtained. Aluminum alloys have gained considerable attention in recent years. Many extensive studies have been done in the past to simultaneously improve the strength and ductility by optimizing the heat treatment cycle for pure Al and Al alloys. [10] Recently, Dhal et al. [11] studied the mechanical proper- ties and microstructural behavior of commercially pure Al subjected to CYR and subsequent annealing at 150 °C for 30 minutes. It was found that the good combination of strength and ductility was achieved by KANDARP CHANGELA and RAVI KUMAR DIGAVALLI are with the Department of Mechanical Engineering, Indian Institute of Technology Delhi, New Delhi, 110016, India. Contact email: kandarp.changela06@gmail.com HARIHARAN KRISHNASWAMY is with the Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai, Tamil Nadu, 600036, India. Manuscript submitted June 28, 2019. Article published online November 18, 2019 648—VOLUME 51A, FEBRUARY 2020 METALLURGICAL AND MATERIALS TRANSACTIONS A