Cold-rolled Grains Research Articles

Microstructure, Texture, and Mechanical Properties of Friction Stir Spot-Welded AA5052-H32: Influence of Tool Rotation Rate.

Friction stir spot welding (FSSW) of similar AA5052-H32 joints has numerous benefits in shipbuilding, aerospace, and automotive structural applications. In addition, studying the role of tool rotation speed on the microstructure features, achieved textures, and joint performance of the friction stir spot-welded (FSSWed) joint still needs more systematic research. Different FSSWed AA5052-H32 lap joints of 4 mm thickness were produced at different heat inputs using three tool rotation speeds of 1500, 1000, and 500 rpm at a constant dwell time of 2 s. The applied thermal heat inputs for achieving the FSSW processes were calculated. The produced joints were characterized by their appearance, macrostructures, microstructures, and mechanical properties (hardness contour maps and maximum tensile-shear load) at room temperature. The grain structure and texture developed for all the FSSWed joints were deeply investigated using an advanced electron backscattering diffraction (EBSD) technique and compared with the base material (BM). The main results showed that the average hardness value of the stir zone (SZ) in the welded joints is higher than that in the AA5052-H32 BM for all applied rotation speeds, and it decreases as the rotation speed increases from 500 to 1000 rpm. This SZ enhancement in hardness compared to the BM cold-rolled grain structure is caused by the high grain refining due to the dynamic recrystallization associated with the FSSW. The average grain size values of the stir zones are 11, 9, and 4 µm for the FSSWed joints processed at 1500, 1000, and 500 rpm, respectively, while the BM average grain size is 40 µm. The simple shear texture with B/-B components mainly dominates the texture. Compared to the welded joints, the joint processed at 500 rpm and a 2 s duration time attains the highest tensile-shear load value of 4330 N. This value decreases with increasing rotation speed to reach 2569 N at a rotation speed of 1500. After tensile testing of the FSSWed joints, the fracture surface was also examined and discussed.

Fast and simple method for Goss texture evaluation by neutron diffraction

Requirement of low power losses is one of the crucial demands laid on properties of electric steel sheets used in construction of various magnetic circuits. For cold-rolled grain- oriented (CRGO) Fe-3%Si sheets used in majority of power distribution transformers, the Goss texture {110}<001> is known to provide the best utility properties (low power loses, high magnetic permeability). Due to the coarse grain size of CRGO steel, neutron diffraction (ND) is dominantly used to characterize the sheets' texture in order to achieve statistically significant data. In this paper, we present a fast and simple method for characterization of Goss texture perfection level in CRGO steel sheets based on monochromatic ND. The method is tested on 8 samples differing in fabrication technology and magnetic properties. Satisfactory performance of the method and its suitability for a detail texture analyses is tested by juxtaposition of the obtained textural and the magnetic characteristics measured by Barkhausen method.

Grain boundary sliding at high temperature deformation in cold-rolled ODS ferritic steels

A tensile test was performed at a loading direction perpendicular to elongated cold-rolled grains, and it confirmed the step of the scratched lines across the grain boundaries on the specimen surface, providing evidence for grain boundary sliding in oxide dispersion strengthened (ODS) steels. Dynamic recovery within the grains was also observed, and a simple model was constructed that consisted of grain boundary sliding and mismatch accommodation induced by vacancy flow. It was confirmed that such grain boundary sliding was suppressed in ODS steel relative to iron as a result of the pinning of the dislocation movement by the dispersed oxide particles.

Evolution of corrosion damage to cold rolled grain oriented steel sheets under rainwater followed by ambient atmosphere exposure

Corrosion damage to cold rolled grain oriented (CRGO) steel sheets with inorganic insulation coating was studied. The coating damage and corrosion on the sheets were analyzed via visual as well as stereomicroscopic imaging, and based on the examinations the sheet surfaces were classified into three categories namely coating intact (Type A), coating damaged (Type B), and coating damage followed by corrosion (Type C). The sheets’ surfaces were examined with scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) to establish the extent of the coating damage and corrosion. Furthermore, core loss measurements were carried out to check the quality of the CRGO sheets. To understand the evolution of corrosion under rainwater followed by ambient atmosphere exposure at coastal regions, the sheet samples were kept immersed in simulated rainwater for 4h followed by placing them in ambient atmosphere for seven consecutive days (atmospheric corrosion test). Corrosion was absent on the sheet samples with the coating intact while other sheet samples with the coating damaged or having corroded spots suffered from selective corrosion.

Microstructure, Texture and Recrystallisation Mechanisms of an Al-20%Sn Deformation Processed Metal-Metal Composite

Al-Sn alloys for tribological applications are industrially important alloys which have attracted little attention over their history. Being cold rolled directly from thin cast slabs and consisting of two ductile phases, their processing and physical behaviour are distinct from classical Al-Alloys. During cold rolling, the coarse-grained, random texture of the slab is transformed into the classical rolling texture of a fine-grained Al-alloy, with elongated Al-grains delimited by thin Sn-ribbons. During annealing at 300°C, the interior of the Al-grains recrystallises rapidly while the liquid Sn-phase migrates toward Al-grain triple lines to form a reticular structure. A weak texture, dominated by Goss and P is produced. Grain growth within the original cold-rolled grains is fast, but once the recrystallised grain size reaches the length scale of the second-phase distribution, it slows down and both phases coarsen simultaneously, accompanied by a significant texture change.

Effect of annealing on the microstructure and mechanical properties of cold rolled Fe–24Mn–3Al–2Si–1Ni–0.06C TWIP steel

Fe–24Mn–3Al–2Si–1Ni–0.06C TWinning Induced Plasticity (TWIP) steel was 42% cold-rolled and isochronally annealed at temperatures between 600 and 850 °C. Optical, secondary and transmission electron microscopy found that a majority of as cold-rolled grains contain a large fraction of primary twin densities and a smaller fraction of secondary twins. Partially recrystallised microstructures comprise a mix of recrystallised grains and annealing twins as well as remanent deformed grains with heavy dislocation substructures and deformation twins. Both deformation and annealing twins follow the {1 1 1}〈1 1 2〉 relationship. All partially recrystallised samples exhibited four work hardening regions and a decreasing twinning onset stress with greater percentage softening. A modification to the Hollomon–Ludwigson scheme is suggested to empirically account for the effect of strain on microstructural refinement.