Sushil Kumar Mishra

Effect of Strain and Strain Path on Texture and Twin Development in Austenitic Steel with Twinning-Induced Plasticity

High-manganese (15 to 30xa0wtxa0pct) austenitic steels exhibit extreme strain hardening because of twinning with increased strain. Twinning in these low stacking fault materials promotes retention of the austenitic microstructure and impedes dislocation motion. A dearth of information is available concerning the extent to which strain path influences twinning in so-called twinning-induced plasticity (TWIP) steels. The present study focuses on the influence of strain level and strain path on texture and twinning in a high-Mn content TWIP steel (Fe17.2Mn0.6C). Electron back-scatter diffraction was employed to measure the twin fraction, twin deviation, twin boundary length, grain misorientation, and volume fraction of different texture components as a function of both uniaxial and biaxial deformation. This information, which is part of the necessary first step toward linking crystallographic texture and twinning to mechanical properties, was used to quantitatively assess the extent to which these critical metallurgical features depend on the amount of straining and the strain path.

Postanneal Mechanical Properties of Prestrained AA5182-O Sheets

The effects of different prestrain levels, paths, and subsequent annealing on the postannealing mechanical properties of AA5182-O were investigated. Aluminum sheet specimens were prestrained in uniaxial, plane strain, and equibiaxial tension to several equivalent strain levels, annealed at 350 °C for short (10 s) and long (20 min) durations and then tested for postannealing mechanical properties, including tensile properties, anisotropy, and forming limits. The tensile properties, R-values at 0, 45, and 90 deg relative to the sheet rolling direction, and forming limit diagrams (FLDs) exhibited dependencies on prestrain and annealing history. The importance of the process variables and their effects were identified via designed experiments and analysis of variance. Three-dimensional digital image correlation, which captured the onset of local necking, was employed in the FLD development. Texture in the as-received and deformed sheets was investigated with electron backscatter diffraction and provided a means for linking prestrain and static recovery or recrystallization with microstructure. This guided the understanding of the mechanical property changes observed after preforming and annealing. Ultimately, the expanded forming limit curve demonstrated the advantage of annealing in extending the formability of strained.

Recovery quantification and onset of recrystallization in aluminium alloys

Novel forming processes for light metal alloys utilize recovery and recrystallization to extend their total elongation and enhance formability. To attain optimum efficiency in such processes, it is necessary to understand and quantify the kinetics of recovery and recrystallization in work-hardened metal alloys. An electron backscatter diffraction based method, using local average orientation spread, is shown to identify the end of recovery as well as the onset of recrystallization. Local average orientation spread results from dislocation flux and storage during plastic deformation and hence, captures the evolution of static recovery process. The method has been demonstrated using pre-strained Al–Mg alloys. The recovery kinetics is shown to be consistent with results from dislocation density based recovery models. In addition, a direct observation of the coexistence of static recrystallization and recovery illustrates competing processes for energy minimization.

Annealing response of AA5182 deformed in plane strain and equibiaxial strain paths

The annealing response of AA5182 Al–Mg alloy deformed to an effective prestrain of u2009=u20090.15 via plane strain and equibiaxial strain paths is compared. The comparison is done at two temperatures namely, 623 and 673u2009K. The recovery, recrystallization and grain growth behaviour of this alloy is studied by electron backscatter diffraction and dislocation density estimation using X-ray line broadening analysis. It is found that recrystallization is slower in equibiaxial deformation condition compared to that in plane strain deformation condition during annealing. Significant recrystallization is observed after annealing for 60u2009s at 673u2009K and for 480u2009s at 623u2009K following plane strain deformation. Furthermore, significant recrystallization is associated with lower grain growth at 673u2009K (∼55u2009μm) as opposed to that at 623u2009K (∼75u2009μm). The results are explained on the basis of differences in both the strain paths.

Post-Anneal Mechanical Properties of Pre-Strained AA5182-O Sheets

The effects of different pre-strain levels, paths and subsequent annealing on the post-annealing mechanical properties of AA5182-O were investigated. Aluminum sheet specimens were pre-strained in uniaxial, plane strain and equibiaxial tension to several equivalent strain levels, annealed at 350°C for short (10 seconds) and long (20 minutes) durations, and then tested for post-annealing mechanical properties, including tensile properties, anisotropy and forming limits. The tensile properties, R-values at 0°, 45° and 90° relative to the sheet rolling direction, and forming limit diagrams (FLDs) exhibited dependencies of pre-strain and annealing history. The importance of the process variables and their effects were identified via designed experiments and analysis of variance. Three-dimensional digital image correlation, which captured the onset of local necking, was employed in the FLD development. Texture in the as-received and deformed sheets was investigated with electron backscattered diffraction and provided a means for linking prestrain and static recovery or recrystallization with microstructure. This guided the understanding of the mechanical property changes observed after preforming and annealing. Ultimately, the expanded forming limit curve demonstrated the advantage of annealing in extending the formability of strained AA5182-O.Copyright