Effect of Deformation on Precipitation and the Microstructure Evolution during Multistep Thermomechanical Processing of Al-Zn-Mg-Cu Alloy

Abstract

In order to obtain fine grained structure efficiently, a new multi-step rolling process (MSR: pre-deformation + intermediate annealing + hot deformation) was applied in Al-Zn-Mg-Cu plates. Conventional hot rolling (CHR) was also carried out as a contrast experiment. The evolution of microstructures and improvement of mechanical properties were analyzed by optical microscope, scanning electron microscope, transmission electron microscope, X-ray diffractometer, and tensile tests. The results show that the MSR process can obtain finer longitudinal grain size and better mechanical properties than CHR, which can be explained as follows: spheroidization of precipitates wrapped by high density dislocations could be promoted by increased pre-deformation; numerous ordered substructures were formed during short-period intermediate annealing at high temperature; in the subsequent hot rolling process, the retained spherical precipitates pinned dislocations and boundaries. With the increase of accumulated strain, low angle grain boundaries gradually transformed into high angle grain boundaries, leading to grain refinement. With the increased pre-deformation (MSR1 20 + 60%, MSR2 40 + 40%, MSR3 60 + 20%), the effect of grain refinement and plasticity improvement gradually weakened. The optimum thermomechanical process (MSR1 solid solution + pre-deformation (300 °C/20%) + intermediate annealing (430 °C/5 min) + hot deformation (400 °C/60%)) was obtained, which can increase elongation by ~25% compared with the CHR process, while maintaining similar high strength for reduced longitudinal grain size.

Characterization of Precipitation in 7055 Aluminum Alloy by Laser Ultrasonics

“…The shape variables of the aluminum alloy are controlled by changing the amount of reduction during the rolling process. It has been shown that as the reduction rates increases, a dynamic precipitation process [28,29] occurs during the deformation process, and at the same time, the fine grain strengthening effect of the grain refinement is gradually refined. Such a large plastic deformation also causes the precipitation size change, and more deformation defects are introduced due to the increased deformation amount (such as point defects, dislocations, and deformation), these structurally large defects will become a rapid diffusion channel of solute atoms, thereby accelerating atomic diffusion and promoting the growth of precipitated phase particles, so the size of the precipitated phase increases with the deformation increase.…”

The Effect of Ecap Processing to Hardness, Surface Morphologi, and Corrosion Resistance of 6061 Aluminium Alloys

“…Some researchers revealed that decreasing grain size using ECAP could increase the corrosion resistance of Al-Mg and pure Mg alloys [13]. It also reported that the decreasing hardness properties resulted from the increasing number of ECAP passes [14]. In this paper, the effect of ECAP number of the pass in the cryogenic environment has been investigated on hardness, microstructure, and corrosion properties of Al 6061.…”

Investigation of deformation behavior and strain-induced precipitations in Al–Zn–Mg–Cu alloys across a wide temperature range

“…Figure 19 presents the XRD patterns of the alloy subjected to compression deformation at various temperatures. In the analysis of XRD spectra of 7055 aluminum alloy from references, it was observed that the prominent diffraction peaks of the MgZn 2 phase are typically found at approximately 32.0° and 41.6° 2θ positions [43][44][45] . The XRD patterns from this experiment were matched against the peak positions reported in the references to confirm the presence of the MgZn 2 phase in the 7055 aluminum alloy studied in this paper.…”