Comparison of Hot Deformation Behavior Characteristics Between As-Cast and Extruded Al-Zn-Mg-Cu (7075) Aluminum Alloys with a Similar Grain Size.

Jeong Jeong,Kim Kim

doi:10.3390/ma12233807

Abstract

The hot compressive behavior and processing maps of as-cast and extruded 7075 aluminum alloys with a similar grain size (320–350 μm) were studied and compared, which allows us to directly observe the effect of segregated phases in the as-cast microstructure on the deformation behavior and hot workability of 7075 alloys. In the as-cast alloy, the compound phases segregated along the interdendritic interfaces within the interiors of original grains provided the additional sites for continuous dynamic recrystallization via the particle stimulation nucleation mechanism. As a result, the as-cast alloy exhibited higher fractions of recrystallized grains and smaller grain sizes than the extruded alloy after compression. The stress exponent values of the as-cast alloy were smaller than those of the extruded alloy. In the processing maps, the domain associated with high power dissipation efficiencies (≥35%) occurred in a wider temperature range in the as-cast alloy compared to the extruded alloy. The segregated phases that remained undissolved in the as-cast alloy after compressive deformation could be effectively eliminated during the solid solution treatment (753 K for 2 h) for T6 aging applied after hot compression. The current results suggest the possibility and advantage of omitting the extrusion step when preparing 7xxx aluminum forging or extrusion feedstocks for hot working. The proposed method can be applied to other precipitation hardenable aluminum alloys.

Highlights

The Al-Zn-Mg-Cu aluminum alloy system (7xxx series) has a high strength-to-density ratio and good toughness coupled with good resistance to stress corrosion cracking [1,2,3,4]
The presence of a high fraction of low-angle grain boundaries (0.81) and a very low fraction of dynamically recrystallized grains (0.03) in the extruded microstructure indicate that Dynamic recovery (DRV) mainly occurred during the extrusion process
The maximum fractions of DRX grains and high-angle grain boundaries (HAGBs) are less than 0.2 and 0.4 in the as-cast and extruded alloys, respectively, indicating that DRV was dominant during hot deformation in both alloys in the investigated experimental range

Summary

Introduction

The Al-Zn-Mg-Cu aluminum alloy system (7xxx series) has a high strength-to-density ratio and good toughness coupled with good resistance to stress corrosion cracking [1,2,3,4]. Due to these properties, it has been widely used in the aerospace and automobile industries for heavy structural applications [5,6,7]. Yang et al [14] studied the hot deformation behavior and processing maps of an extruded 7075 alloy in the temperature range of 593–753 K and in the strain rate range of 10−3 –1 s−1. Yang et al [15]

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Discussion

Conclusion