Abstract
The hot deformation behavior of an Al-Zn-Mg-Cu alloy was investigated by hot compression test at deformation temperatures varying from 320 to 440 °C with strain rates ranging from 0.01 to 10 s−1. The results show that the Mg(Zn, Cu)2 particles as a result of the sufficient static precipitation prior to hot compression have an influence on flow softening. A constitutive model compensated with strain was developed from the experimental results, and it proved to be accurate for predicting the hot deformation behavior. Processing maps at various strains were established. The microstructural evolution demonstrates that the dominant dynamic softening mechanism stems from dynamic recovery (DRV) and partial dynamic recrystallization (DRX). The recrystallization mechanism is continuous dynamic recrystallization (CDRX). The microstructure observations are in good agreement with the results of processing maps. On account of the processing map and microstructural observation, the optimal hot processing parameters at a strain of 0.6 are at deformation temperature range of 390–440 °C and strain rate range of 0.010–0.316 s−1 with a peak efficiency of 0.390.
Highlights
Al-Zn-Mg-Cu alloys are extensively used for structural applications of aerospace, petroleum and gas, and automotive industries due to their high strength-to-weight ratio, good stress corrosion cracking resistance, and high fracture toughness [1,2,3,4,5]
The cast ingot was subjected to a two-step homogenization that consisted of a low-temperature step 420 ◦ C for 24 h followed by a high-temperature step at 465 ◦ C for 72 h, after which it was machined at 420 °C for 24 h followed by a high-temperature step at 465 °C for 72 h, after which it was to cylindrical compressive samples that were 10 mm in diameter and 15 mm in height
The Mg(Zn, Cu)2 particles as a result of the sufficient static precipitation prior to hot compression have an influence on the flow behavior by effectively pinning the dislocation during hot compression
Summary
Al-Zn-Mg-Cu alloys are extensively used for structural applications of aerospace, petroleum and gas, and automotive industries (aircraft fuselage, drill pipe, etc.) due to their high strength-to-weight ratio, good stress corrosion cracking resistance, and high fracture toughness [1,2,3,4,5]. Hot forming (rolling, forging, extrusion, etc.) is a significant processing technique for manufacturing these structural components. As a newly developed Al-Zn-Mg-Cu alloy used in oil drilling pipe, the studied alloy shows a relatively high strength and excellent thermal stability as compared to the conventional Al-Zn-Mg-Cu alloy with low Zn/Mg ratio. For the former alloy, high Zn/Mg ratio leads to a denser precipitation of η0 phase. Oil drilling pipes are fabricated by hot extrusion. Material flow behavior is often very complicated during hot extrusion. Various metallurgical phenomena often take place, which greatly influence the material flow
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