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Investigation of mechanical properties, formability, and anisotropy of dual phase Mg-7Li-1Zn

The development of a novel forming limit diagram under nonlinear loading paths in tube hydroforming

Hot metal gas forming (HMGF) is a desirable way for the automotive industry to produce complex metallic parts with poor formability, such as aluminum alloys. A simple hot gas forming method was developed to form aluminum alloy tubes using flame heating. An aluminum alloy tube was heated by a flame torch while the tube was rotated and compressed using a lathe machine and simultaneously pressurized with a constant air pressure. The effects of the internal pressure and axial feeding on expansion and wall thickness distribution were examined. The results showed that the proposed gas forming method was effective for forming aluminum alloy tubes. It was also indicated that axial feeding is a vital parameter to prevent reductions in wall thickness by supplying the material flow during the forming process.

Hot Gas Forming of Aluminum Alloy Tubes Using Flame Heating

The mechanical properties of tubes in hoop directions can be measured with ring hoop tensile test (RHTT). This test involves placing a ring sample of tube over the two D-shaped mandrels which can be parted with a testing machine. In this article, the goal was measuring the directional anisotropy coefficients of hydroformed AA7020-T6 tubes (r0, r45, and r90) to predict forming limit diagram (FLD). Due to deriving anisotropy coefficients in different directions, various tensile tests should be performed for the tube. For longitudinal and circumferential samples, a simple tensile test and ring hoop tensile test were applied to obtain r0 and r90, respectively. Additionally, for testing in 45° to the rolling direction, a new testing method which is inspired by RHTT was used to find r45. Afterwards, forming limit diagram of this aluminum alloy was predicted theoretically based on the Marciniak-Kuczynski (M-K) model and Voce hardening law. Since, one of the important factors in gaining accurate FLDs is yield function. Two advanced yield functions, BBC2008 and YLd2011, were selected. These advanced yield functions can describe material’s anisotropy behavior better than the classical ones. The importance of the directional anisotropy coefficients and other data obtained by tensile tests was in calibration of yield functions. Good agreement between the FLD derived under the influence of a calibrated yield function and the experimental FLD supports the present calibration.

Measurement of directional anisotropy coefficients for AA7020-T6 tubes and prediction of forming limit curve

Forming limit diagram (FLD) is one of the formability criteria which is a plot of major strain versus minor strain In the present study, Gurson-Tvergaard-Needleman (GTN) model is used for FLD prediction of aluminum alloy 6061 Whereas correct selection of GTN parameters’ is effective in the accuracy of this model, anti-inference method and numerical simulation of the uniaxial tensile test is used for identification of GTN parameters Proper parameters of GTN model is imported to the finite element analysis of Nakazima test for FLD prediction Whereas FLD is dependent on forming history and strain path, forming limit stress diagram (FLSD) based on the GTN damage model is also used for forming limit prediction in the numerical method Numerical results for FLD, FLSD and punch’s load-displacement are compared with experimental results Results show that there is a good agreement between the numerical and experimental results The main drawback of numerical results for prediction of the right-hand side of FLD which was concluded in other researchers’ studies was solved in the present study by using GTN damage model

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Forming limit diagram prediction of 6061 aluminum by GTN damage model

In this study, forming limit diagram (FLD) of tubular material (Al 7020-T6) was determined numerically and experimentally. A set of experimental bulge tests were carried out to determine FLD under combined internal pressure and axial feeding. Also, a numerical approach which is based on the acceleration of plastic strain (i.e., the second derivation) was applied to compute the hydroforming strain limit diagram. Based on this method, the localized necking would be started when the acceleration of the max plastic strain got its maximum value. Finally, the numerical FLD was verified by experimental test results on the aluminum tube 7020-T6 and a good agreement between the proposed method and the experimental works was observed.

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Arvand Afshar

Papers

Numerical and experimental study of bursting prediction in tube hydroforming of Al 7020-T6