Dislocation density based model for plastic deformation and globularization of Ti-6Al-4V

In order to study the high-temperature flow stress of commercial purity aluminum (AA1070), isothermal hot compression tests were conducted at the deformation temperatures varying from 350 to 500 °C and strain rates ranging from 0.005 to 0.5 s−1. The results showed that the flow stress of AA1070 was evidently affected by both the deformation temperature and strain rate. The influence of strain was also incorporated in the constitutive equation by considering the effects of strain on material constants which are consist of β, α, n, A and activation energy Q. The predicted flow stress curves using the proposed constitutive equations well agree with the experimental results of the flow stress for AA1070.

Constitutive equations for elevated temperature flow behavior of commercial purity aluminum

Comparative study of constitutive modeling for Ti–6Al–4V alloy at low strain rates and elevated temperatures

Magnesium (Mg) alloys have been extensively used in various fields, such as aerospace, automobile, electronics, and biomedical industries, due to their high specific strength and stiffness, excellent vibration absorption, electromagnetic shielding effect, good machinability, and recyclability. Friction stir processing (FSP) is a severe plastic deformation technique, based on the principle of friction stir welding. In addition to introducing the basic principle and advantages of FSP, this paper reviews the studies of FSP in the modification of the cast structure, superplastic deformation behavior, preparation of fine-grained Mg alloys and Mg-based surface composites, and additive manufacturing. FSP not only refines, homogenizes, and densifies the microstructure, but also eliminates the cast microstructure defects, breaks up the brittle and network-like phases, and prepares fine-grained, ultrafine-, and nano-grained Mg alloys. Indeed, FSP significantly improves the comprehensive mechanical properties of the alloys and achieves low-temperature and/or high strain rate superplasticity. Furthermore, FSP can produce particle- and fiber-reinforced Mg-based surface composites. As a promising additive manufacturing technique of light metals, FSP enables the additive manufacturing of Mg alloys. Finally, we prospect the future research direction and application with friction stir processed Mg alloys.

Friction Stir Processing of Magnesium Alloys: A Review

Microstructure study and constitutive modeling of Ti–6Al–4V alloy at elevated temperatures

The high-temperature deformation behavior of the as-forged TC17 titanium alloy was studied based on the results of thermal compression simulation tests. Additionally, the effects of strain rate, temperature and true strain on the flow stress were analyzed using orthogonal experimentation and variance analysis. The results indicated that all deformation parameters exerted significant influence on flow stress, with temperature and strain having the largest and least influence, respectively. Thereafter, a constitutive equation based on modified nonlinear regression was proposed. The error analysis results showed that the flow stress of the as-forged TC17 alloy could be predicted by the obtained constitutive equation. The effect of deformation parameters on the microstructure was investigated by EBSD and TEM.

Research on Hot Deformation Behavior of As-Forged TC17 Titanium Alloy

Large-sized frame forging of Ti-alloy is an important forced component of aircraft. The frame forging has complicated shape which leads to great difficulties in deformation. Some defects may be produced during the forming process such as un-filling or overlapping. Preform design is an effective method for producing qualified forging. In this article, a new method based on 3-D electrostatic field simulation is proposed to design preform of a large-sized frame forging of Ti-alloy and a geometric transformation method is introduced to obtain the preform dimension. In order to select more suitable preform of large-sized frame forging, FEM software Deform-3D is employed to simulate the isothermal forming process of designed preform. Deformation uniformity index ψ is introduced as a criterion to judge the forging quality and the most appropriate preform is obtained by virtual orthogonal test design.

Preform Design for Large-Sized Frame Forging of Ti-Alloy Based on 3-D Electrostatic Field Simulation and Geometric Transformation

Elevated Temperature Compression Deformation Behavior of Commercial Pure Zr Combined with the Constitutive Equation and Processing Map

As a component layer of layered composites, pure Ti renders the advantages of high specific strength, low density, low elastic modulus, high-temperature corrosion resistance and excellent biocompatibility. Accordingly, it has broad application prospects in the field of layered composites. In order to study the hot deformation behavior and microstructural evolution of pure Ti during roll bonding processing, hot compression tests were carried out at temperatures of 550–700 °C and strain rates of 0.01–10 s−1 with a true strain of 0.91 on the Gleeble-3500 thermal simulation machine. Arrhenius constitutive model was used to predict the flow behavior of pure Ti, and the correlation coefficient between the experimental and predicted values reached 0.92313. Based on the hot processing maps, it was found that the peak efficiency of power dissipation (η) region occurs at 650–700 °C/0.01–0.02 s−1. At a strain of 0.9, the optimal processing region is found to be 650–680 °C/0.01–0.015 s−1 with the power dissipation value about 0.59–0.62. At high temperature/low strain rate (650 °C/0.01 s−1), the dynamic recrystallization (DRX) phenomenon is obvious in pure Ti. With the increase of strain rate or the decrease of temperature, the discontinuous dynamic recrystallization (DDRX) nucleates at the original grain boundary in the form of grain boundary bow out, and gradually grows by consuming the original deformed grains, forming a typical “necklace” structure. 

Deformation behavior and microstructural evolution of pure Ti produced by hot compressing

Based on the flow stress data obtained from the isothermal hot compression tests, the processing maps of Ti-6Al-4V alloy were developed based on the instability criteria of Prasad, Malas, and Murty. The validation of the processing maps was achieved by investigating the microstructures of compressed Ti-6Al-4V alloy specimens. The results showed that the power dissipation maps obtained using the criteria of Prasad and Murty exhibited similar distribution, whereas the instability domains obtained by various instability criteria had great differences. Microstructure analysis showed that the instability domains determined by Murty’s criterion were more accurate than those determined using other criteria.

Jun Cai

Papers

Research on Hot Deformation Behavior of As-Forged TC17 Titanium Alloy

Preform Design for Large-Sized Frame Forging of Ti-Alloy Based on 3-D Electrostatic Field Simulation and Geometric Transformation

Elevated Temperature Compression Deformation Behavior of Commercial Pure Zr Combined with the Constitutive Equation and Processing Map

Deformation behavior and microstructural evolution of pure Ti produced by hot compressing

Development and Validation of Processing Maps for Ti-6Al-4V Alloy Using Various Flow Instability Criteria