Abstract
In this study, AA2519 alloy was initially processed by multi axial forging (MAF) at room and cryogenic temperatures. Subsequently, the microstructure and the mechanical behavior of the processed samples under quasi-static loading were investigated to determine the influence of cryogenic forging on alloys’ subgrains dimensions, grain boundaries interactions, strength, ductility and toughness. In addition, the failure mechanisms at the tensile rupture surfaces were characterized using scanning electron micro-scope (SEM). The results show significant improvements in the strength, ductility and toughness of the alloy as a result of the cryogenic MAF process. The formation of nanoscale crystallite microstructure, heavily deformed grains with high density of grain boundaries and second phase breakage to finer particles were characterized as the main reasons for the increase in the mechanical properties of the cryogenic forged samples. The cryogenic processing of the alloy resulted in the formation of an ultrafine grained material with tensile strength and toughness that are ~41% and ~80% higher respectively after 2 cycles MAF when compared with the materials processed at ambient temperature. The fractography analysis on the tested materials shows a substantial ductility improvement in the cryoforged (CF) samples when compared to the room temperature forged (RTF) samples which is in alignment with their stress-strain profiles. However, extended forging at higher cycles than 2 cycles led only to increase in strength at the expense of ductility for both the CF and RTF samples.
Highlights
Severe Plastic Deformation (SPD) may be described as a metal forming process in which an ultra-large plastic strain is applied into a bulk metal leading to a gradual formation of nano/ultrafine grained structures [1]
The cryogenic processing of the alloy resulted in the formation of an ultrafine grained material with tensile strength and toughness that are ~41% and ~80% higher respectively after 2 cycles multi axial forging (MAF) when compared with the materials processed at ambient temperature
The dynamic recovery is systematically stopped at the liquid nitrogen temperature which leads to diminishing dislocation mobility and allowing the accumulation of dislocation density to achieve a higher steady state level
Summary
Severe Plastic Deformation (SPD) may be described as a metal forming process in which an ultra-large plastic strain is applied into a bulk metal leading to a gradual formation of nano/ultrafine grained structures [1]. MAF is a relatively simple SPD process that consists of repeated compression in three orthogonal directions associated with a change in the axis to 90 ̊ in every pass leading to the attainment of a uniform texture with low aspect ratio grains within the material. Does it have the potential for scaling up of the processed products, but it preserves the original shape with least distortion even after several cycles, which is ideal for industrial applications [9]
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