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The demand for lightweight tubular products, designed specifically for transportation and recreational applications, is currently on the rise. In general, performance increase and energy cost reduction are the main reasons justifying the need for these specialty products. Hence, to reach these goals, both industries are turning to complex-shaped tu...
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The hot deformation behaviour of one 7XXX series aluminium alloy, 7A04, has been studied by conducting isothermal hot compression tests with degree of compression up to 55% at the temperature ranging from 350 °C to 480 °C and strain rates ranging from 0.002 s⁻¹ to 20s⁻¹. Based on characteristic of the flow stress obtained from those tests, an extended Voce equation, which constant parameters were modified as Arrhenius-type type equation, was given and used to calculate the flow stresses under the conditions of the hot deformation. The parameters of extended Voce equation were determined by experimental results. The comparison between the experimental and predicted flow stress values at the hot compression parameters range indicated good agreement. The average absolute relative error, root mean square error and the correlation coefficient were found to be 4.9%, 4.8 MPa and 0.997, respectively, which confirmed the extended Voce model had good accuracy. Additional, a finite element simulation model of isothermal hot compression process was used to verify the new Voce equation and the results verified the accuracy of the new equation. The main softening mechanism of the hot deformation was dynamic recovery and was confirmed by optical microstructures.
In this paper a study on the innovative process of hot tube metal gas forming and hot press hardening (Hot
Metal Gas Press Hardening – HMG-PH) is presented. The aim is to provide new insights into the influence of
process variables (gas pressure, tool temperature, tube pre-heating temperature, etc.) on the hardening
phenomenon and on the quality of the produced tubular components (calibration radii, minimum wall
thickness, etc.). Several experiments are described on two different kinds of steel, using a reference die
geometry, specifically designed for investigating the typical critical issues of the process. The study
demonstrates that the hardening phenomenon is strongly local not only because the hardness distribution is
non-uniform over the final part, but especially because the hardening of different regions depends on
different process parameters: in regions that need calibration, hardening is governed more by the pressure
vs. time curve, i.e. by its rate and its maximum value and less by the tool temperature; in regions that rapidly
go in contact to the die, hardening is governed more by the tool temperature and less by the pressure vs. time
curve. Another relevant conclusion is that an optimal value of pressurization rate can be found that
maximizes formability. Finally, the study proves that, on the formed tubes, obtaining small calibration radii
and obtaining high values of hardness are conflicting objectives. The physical mechanisms behind these
behaviours are discussed.
