Gang Fang

Investigation of thermal formability of aluminum alloy 4032

The deformation behavior of a 4032 aluminum alloy by hot compression has been investigated. It was found that the flow stress was strongly dependent on temperature as well as strain rate. The strain rate-sensitive coefficients were calculated at different temperatures. The experimental stress-strain data are fitted by means of the model earlier advanced by Sah et al. The Sellars-Tegart-Garofalo (STG) model is used to obtain activation energy values, which vary with the strain rate and strain.

FEM-Assisted Design of a Multi-Hole Pocket Die to Extrude U-Shaped Aluminum Profiles with Different Wall Thicknesses

Wide, thin-wall profiles exiting simultaneously from a multi-hole die during aluminum extrusion tend to have different velocities and deflect from the straight line. The pockets in front of the die orifices are often used to balance the metal flow and equalize the velocities. In practice, the effect of a pocket die design on metal flow becomes known, only after the die is manufactured and a trial extrusion run is completed. The present research was intended to demonstrate the feasibility of using FEM simulation to predict metal flow, thereby reducing or hopefully eliminating trial extrusion runs. The extrusion of U-shaped profiles with different wall thicknesses through a multi-hole pocket was taken as an example to show the scope of adjusting the die pocket to regulate metal flow. The effect of pocket shape on metal flow was evaluated. It is clear that 3D FEM simulation can indeed be effectively used to optimize die design, before the die design is finalized.

Formability Evaluation of Aluminum Alloy 6061-T6 Sheet at Room and Elevated Temperatures

The formability of aluminum alloy 6061-T6 sheet was evaluated, and the effects of temperature and strain rate on the formability were analyzed. Uniaxial tension tests and Nakajima tests were conducted at room temperature to obtain the constitutive parameters of AA 6061-T6 and establish the forming limit diagram (FLD), respectively. Moreover, uniaxial tension tests were performed at the temperatures ranging between 180 and 380xa0°C and the strain rates ranging between 0.0005 and 0.05xa0s−1, and the constitutive equations of AA 6061-T6 were established. Nakajima tests at temperature 330xa0°C and two forming speeds (15 and 150xa0mm/min) were carried out to evaluate the formability of AA6061-T6 at elevated temperatures. In consequence, FLDs under different forming conditions were established and compared. Experimental results showed that the forming limit of AA 6061-T6 increased with the increasing temperature and the decreasing forming speed. The present investigation presented the formability of AA 6061-T6 under different forming conditions, which provided a guidance to design the warm/hot forming of AA 6061 sheet. The FLDs and constitutive equations established through these experiments will be used to predict the forming defects in the forming process design.

FE Simulation of Extrusion to Produce a Thin-Walled Wide Profile through a Spreading Pocket Die

In the present case study, finite element (FE) simulation was performed to evaluate the design of a spreading pocket die by analysing the metal flow during the extrusion of the 6061 alloy to produce a thin-walled wide profile for ground transportation applications. The results obtained from the FE simulation were in good agreement with those from industrial extrusion trials. The velocity and temperature non-uniformities on the profile cross section, revealed from the FE simulation, suggested the die bearing area for die correction. The FE simulation also showed that ram speed had little influence on the velocity non-uniformity but a marked effect on the temperature and temperature distribution of the profile. In the case of extrusion through the spreading pocket die, more heat dissipation from the hotter billet to the die took place, especially when ram speed was low. Therefore, to reach a temperature sufficient for the dissolution of Mg and Si, ram speed must be raised. The FE simulation in the transient state of the extrusion process could give an indicative ram speed for trial extrusion to reach a sufficiently high temperature for the solution treatment on the one hand and to avoid hot shortness on the other hand. It also showed that ram speed had a moderate effect on the breakthrough pressure. Therefore, in the selection of ram speed, attention should be paid to its effect on the maximum profile temperature and temperature distribution.

A Study of Fine Blanking Process by FEM Simulation

Fine blanking process with V-ring was simulated with FEM. The geometric parameters of the die, the punch, the serrated ring and the sheet are modeled. In this paper, some other assumptions are made for the analysis. The workpiece is considered as elastic-plastic material, while the tools are defined as rigid bodies. The damage model taking into account the influence of hydrostatic stress is used to simulate material fracture in blanking. The stress status and forming process are analyzed. Authors also investigated the effect of distance from tooth to die edge on roll-over high. The simulation can reflect the laws of fine blanking process.

Constitutive Behavior and Forming Limit of Mg-Al-Ca-Gd Alloy Sheets at Room and Elevated Temperatures

The constitutive behavior and forming limit of a newly developed magnesium alloy sheet containing rare earth elements (Mg-Al-Ca-Gd) were investigated. Anisotropic constitutive constants were obtained through tensile tests at various temperatures and strain rates. A modified Grosman equation was adopted to describe the constitutive behavior of the magnesium alloy, taking into account the effects of temperature and strain rate. Results revealed that the proper forming temperature and the strain rate for the newly developed magnesium alloy were 210xa0°C and 0.001xa0s−1, respectively. Forming limit curves at room temperature and 210xa0°C were, respectively, established by the combination of hemispherical punch tests and theoretical predictions using a modified Marciniak–Kuczynski model. The accuracy of the theoretical prediction of FLD was discussed. The forming limit of Mg-Al-Ca-Gd alloy sheet increased when heated from room temperature to 210xa0°C.