The hot deformation behavior of extruded AZ80 magnesium alloy was investigated using compression tests in the temperature range of 250–400 °C and strain rate range of 0.001–1.000 s−1. The 3D power dissipation map was developed to evaluate the hot deformation mechanisms and determine the optimal processing parameters. Two domains of dynamic recrystallization were identified from the 3D power dissipation map, with one occurring in the temperature and strain rate range of 250–320 °C and 0.001–0.010 s−1 and the other one occurring in the temperature and strain rate range of 380–400 °C and 0.001–0.003 s−1. In order to delineate the regions of flow instability, Prasad’s instability criterion, Murty’s instability criterion and Gegel’s stability criteria were employed to develop the 3D instability maps. Through microstructural examination, it is found that Prasad’s and Murty’s instability criteria are more effective than Gegel’s stability criteria in predicting the flow instability regions for extruded AZ80 alloy. Further, the 3D processing maps were integrated into finite element simulation and the predictions of the simulation are in good agreement with the experimental results.

This study focuses on deformation characteristics of superalloy IN718 by formulation of a new flow stress model and detailed evaluation of intrinsic workability through the generation of three-dimensional (3D) processing maps with the support of optical microstructural observations. Based on thermomechanical simulation tests using a Gleeble-1500 machine, the flow stress model for superalloy IN718 was built and the flow stress throughout the entire deformation process was described by a peak stress only depending on Zener–Hollomon parameter and strain. The developed model exhibited the strain softening due to dynamic recrystallisation (DRX). The intrinsic workability was further investigated by constructing 3D processing maps. The 3D processing maps described the variations of the efficiency of power dissipation and flow instability domains as a function of strain rate, temperature and strain, from which the favourite deformation conditions for thermomechanical processing of IN718 can be established.

Waves occurring in cold-rolled plates or sheets can be divided into longitudinal and transverse waves. Classical leveling theories merely solve the problem of longitudinal waves, while no well accepted method can be employed for transverse waves. In order to investigate the essential deformation law of leveling for plates with transverse waves, a 2.5-dimensional (2.5-D) analytical approach was proposed. In this model, the plate was transversely divided into some strips with equal width; the strips are considered to be in the state of plane strain and each group of adjacent strips are assumed to be deformation compatible under stress. After calculation, the bending deformation of each strip and the leveling effect of overall plate were obtained by comprehensive consideration of various strips along with the width. Bending of roller is a main approach to eliminate the transverse waves, which is widely accepted by the industry, but the essential effect of bending of roller on the deformation of plates and the calculation of bending of roller are unknown. According to the 2.5-D analytical model, it can be found that, for plates, it is neutral plane offsetting and middle plane elongation or contraction under inner stress that can effectively improve plate shape. Taking double side waves as an example, the appropriate values of bending of roller were obtained by the 2.5-D analytical model related to different initial unevenness, which was applicable to the current on-line adjusting of bending of roller in rolling industry.

The hot deformation stability of extruded AZ61 magnesium alloy was investigated by means of hot compression tests at the temperature range of 250–400 °C and strain rate range of 0.001–1 s−1. The 3D instability maps considering the effect of strain were developed to delineate the regions of unstable flow on the basis of Jonas’s, Semiatin’s, Prasad’s, Murty’s, Gegel’s and Alexander’s criteria. Since non-uniform deformation occurs due to the initial microstructure inhomogeneity, the friction, etc., finite element simulations were performed to determine the position of the specimens which can mostly represent the preset deformation parameter. Detailed microstructural investigation on such position was carried out to examine the validity of the instability maps, and the results indicate that for extruded AZ61 magnesium alloy: (1) Jonas’s and Semiatin’s criteria conservatively predict the instability regions; (2) Gegel’s and Alexander’s criteria inadequately predict the instability regions; (3) Prasad’s and Murty’s criteria provide more effective predictions of the instability regions than Jonas’s, Semiatin’s, Gegel’s and Alexander’s criteria.

In this work, AZ61 magnesium alloy was processed using a new strategy for multidirectional forging (MDF) with an increased strain rate to obtain homogeneous and fine microstructures. The effect of the MDF process on the microstructure and mechanical properties of the alloy was investigated. It was revealed that the grain size decreases, and the homogeneity of the microstructure simultaneously increases, with the number of MDF passes. After four MDF passes, a homogeneous and fine microstructure with the average grain size of ~6.1 μm was achieved. Additionally, dynamic precipitation of the Mg17Al12 phase occurred during the fifth MDF processing pass. The mechanical properties of the AZ61 alloy increased gradually as the number of passes increased from one to four passes, and the sample undergoing MDF exhibited an excellent combination of mechanical properties after the fourth pass, including the yield strength, ultimate strength and elongation to failure, which reached 241 MPa, 303 MPa and 13%, respectively. These values are 97%, 66% and 189% higher, respectively, than for the sample that did not undergo MDF. After the fifth MDF processing pass, the mechanical properties of the alloy decrease sharply, which may be attributed to the dynamic precipitation of the Mg17Al12 phase during this pass.