Hot deformation behaviour and flow stress prediction of 7075 aluminium alloy powder compacts during compression at elevated temperatures

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 534; pp. 624 - 631
• Main Authors: Jabbari Taleghani, M.A., Ruiz Navas, E.M., Salehi, M., Torralba, J.M.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 01-02-2012; Elsevier
• Subjects: Al–Zn–Mg–Cu aluminium alloy; Applied sciences; Constitutive equation; Cross-disciplinary physics: materials science; rheology; Elasticity. Plasticity; Exact sciences and technology; Flow curve; Flow stress prediction; Hot compression; Materials science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Physics; Porous materials; granular materials; Premixed powder; Specific materials; Constitutive equation; Premixed powder; Al–Zn–Mg–Cu aluminium alloy; Hot compression; Flow curve; Flow stress prediction; Hot deformation; Cold pressing; Plastic flow; Temperature effect; Mechanical properties; Al-Zn-Mg-Cu aluminium alloy; Aluminium alloy; Compression test; Porous material; Experimental result; Viscoplasticity; Powder compaction; Stress effects; True stress true strain curve; Activation energy; Zener Hollomon parameter; Flow stress; Strain rate
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2011.12.019

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► The hot deformation behaviours of 7075 aluminium alloy powder compacts are investigated. ► The effect of relative green density is evaluated. ► Flow curves show a peak stress after which the flow stress remains nearly constant. ► Q and material constants are highly dependent on the relative green density. ► A constitutive equation including the variable of relative green density is developed.
In the present study, the hot deformation behaviour of 7075 aluminium alloy powder compacts was studied by performing hot compression tests on a Gleeble 3800 machine. The main objectives were to evaluate the effect of the relative green density on the hot deformation behaviour and to model and predict the hot deformation flow stress of powder compacts using constitutive equations. For this purpose, powder compacts with relative green densities ranging from 83 to 95%, which were prepared by uniaxial cold pressing a commercial pre-mixed powder, were hot compressed at temperatures ranging from 350°C to 450°C and at true strain rates ranging from 0.01s−1 to 10s−1. The true stress–true strain curves of the powder compacts exhibited a peak stress at a critical strain after which the flow stress remained nearly constant. As the deformation temperature increased or the strain rate and green density decreased, a decrease in the peak stress level was observed. The relationship between deformation temperature, strain rate, and the peak flow stress of powder compacts was described by the Zener–Hollomon parameter in an exponential equation containing relative green density compensated material constants and the deformation activation energy. The peak flow stresses calculated from the proposed formula were in good agreement with the experimental results, which confirms the applicability of the employed method for the prediction of the hot deformation flow stress of porous materials with different relative green densities.