Jae Hyung Cho

Determination of volume fractions of texture components with standard distributions in euler space

The intensities of texture components are modeled by Gaussian distribution functions in Euler space. The multiplicities depend on the relation between the texture component and the crystal and sample symmetry elements. Higher multiplicities are associated with higher maximum values in the orientation distribution function (ODF). The ODF generated by Gaussian function shows that the S component has a multiplicity of 1, the brass and copper components, 2, and the Goss and cube components, 4 in the cubic crystal and orthorhombic sample symmetry. Typical texture components were modeled using standard distributions in Euler space to calculate a discrete ODF, and their volume fractions were collected and verified against the volume used to generate the ODF. The volume fraction of a texture component that has a standard spherical distribution can be collected using the misorientation approach. The misorientation approach means integrating the volume-weighted intensity that is located within a specified cut-off misorientation angle from the ideal orientation. The volume fraction of a sharply peaked texture component can be collected exactly with a small cut-off value, but textures with broad distributions (large full-width at half-maximum (FWHM) need a larger cut-off value. Larger cut-off values require Euler space to be partitioned between texture components in order to avoid overlapping regions. The misorientation approach can be used for texture’s volume in Euler space in a general manner. Fiber texture is also modeled with Gaussian distribution, and it is produced by rotation of a crystal located at g0, around a sample axis. The volume of fiber texture in wire drawing or extrusion also can be calculated easily in the unit triangle with the angle distance approach.

Texture evolution of FCC sheet metals during deep drawing process

Abstract The stability of ideal orientations and texture evolution was investigated for FCC sheet metals during deep drawing. Lattice rotation fields around ideal orientations were numerically predicted using a rate-sensitive polycrystal model with full constraint boundary conditions. In order to evaluate the strain path during deep drawing of an AA1050, simulations using a finite element analysis were carried out. The stability of orientations and texture formation was examined at sequential paths such as flange deformation, transition and wall deformation. Depending on the initial location in the blank, the deviation from the plane strain state in the flange deformation path decreased the orientation density around P {0 1 1}〈8 11 11 〉 and shifted the final stable end orientation from P to Yf near {1 1 1}〈 1 1 2〉 . The texture evolution in AA1050 sheet metals during deep drawing was experimentally investigated. The change of orientation density around ideal orientations in the RD and TD samples was in good agreement with the rate-sensitive polycrystal model.

Microtexture Analysis of Friction Stir Welded Al 6061-T651 Plates

Microstructural characteristics of friction-stir-welded Al 6061-T651 with varying rotating and advancing speed were examined by the electron backscattering diffraction (EBSD) installed in field emission-scanning electron microscopy (FE-SEM). It was found that FSW produced an equiaxed fine-grained microstructure in weld zone and the grain size in weld zone decreased up to about 4~6 µm with decreasing rotating speed. The primary textures developed in weld zone were {100}<001>, {110}<001> and {111}<110>. In thermo-mechanical affected zone, the change in grain size was not significant, however, large number of low angle grain boundaries were observed, which seems to be concerned with the formation of subgrains due to the development of dislocation cells.

Microstructure comparison of ZK60 alloy under casting,twin roll casting and hot compression

Abstract The microstructures of ZK60 alloy under conventional direct as-casting (DC), twin roll casting (TRC) and twin roll casting followed by hot compression (TRC-HC) were analyzed by optical morphology (OM), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). The deformation condition of hot compression is 350 °C, 0.1 s −1 . The microstructural evolution under TRC-HC deformation followed by annealing at different temperatures and time was discussed. The results show that TRC provides more modified microstructure compared with DC. Twins are found in TRC processing; dynamic recrystallization (DRX), shear bands and twins are found in TRC-HC. A short annealing time has little effect on hardness, while during a long time annealing, it is found that low annealing temperatures increase the micro-hardness and high temperature decreases it.

Modeling Texture Evolution During Friction Stir Welding of Stainless Steel With Comparison to Experiments

Texture evolution during friction stir welding of stainless steel was investigated using a polycrystal plasticity model together with a three-dimensional, thermomechanically coupled, finite element formulation. The influence of frictional conditions with the tool pin and shoulder on the flow in the through-thickness direction was examined in terms of their impact on the evolving crystallographic texture. Trends in regard to the strengthening and weakening of the texture are discussed in relation to the relative magnitudes of the deformation rate and spin. Finally, the computed textures are compared to electron backscatter diffraction measurements and are discussed with respect to distributions along orientational fibers and the dominant texture components along the fibers.

Microstructure and Mechanical Properties of ZK60 Alloy Sheets during Aging

Variations in microstructure and mechanical properties of ZK60 alloy sheets were investigated with aging time. ZK60 alloy sheets with a thickness of 1mm were prepared from a casting ingot followed by homogenization and warm-rolling. Artificial aging process after solution heat treatment (T6) affected both hardness variations and precipitates distributions with aging time. Hardness variations were related to precipitates, i.e. rod-shaped ( 1 β ′ ) or disc shaped ( 2 β ′ ) particles. Rod-shaped ( 1 β ′ ) precipitates mainly consist of Mg and Zn without Zr.

Effect of Heat Treatment on Microstructure and Mechanical Properties in ZK60 Alloy Sheet

The sheet of ZK60 alloy with a thickness of 1mm was prepared from a casting ingot followed by homogenization and warm-rolling. Variations in microstructure and mechanical properties of ZK60 alloy sheets were investigated during T6 treatment. Especially artificial aging after solution heat treatment affected both precipitates distribution and mechanical properties with aging treatment. Variations of mechanical properties were related to precipitates, i.e. rod-shaped ( 1 β ′ ) or disc shaped ( 2 β ′ ) particles. Around the peak of hardness values, regularly distributed rod-shaped ( 1 β ′ ) precipitates were found. The rod-shaped ( 1 β ′ ) precipitates were oriented with a growth direction of [0001]. When over-aged, rod-shaped ( 1 β ′ ) precipitates were expected to decrease and the density of disc-shaped ( 2 β ′ ) precipitates to change. The rod-shaped ( 1 β ′ ) precipitates mainly consist of {Mg, Zn}, while disc-shaped ( 2 β ′ ) precipitates, {Mg, Zn, Zr} or {Mg, Zn}. In this study the optimum T6 treatment was determined as solution treatment at 430 °C for 6 hours and subsequently aging treatment at 175 °C for 18 hours. At this T6 condition the tensile strength, yield strength and elongation are 321MPa, 280MPa and 16%, respectively.

Microstructure and Mechanical Properties of Severely Deformed Mg-4.5Al-1.0Zn Alloy Processed by Asymmetric Rolling on Ingot and Twin Roll Cast Strip

The twin roll cast Mg-4.5Al-1.0Zn alloy sheets, processed by asymmetric rolling and subsequent annealing were investigated. The asymmetric rolling on Mg-4.5Al-1.0Zn ingot was also studied for comparison in terms of microstructure, texture and mechanical properties of the sheets. The results can be summarized as follows. The rolled sheets show intensively deformed band structures and fine grains due to dynamic recrystallization. After annealing at 375 °C for 1 hr, both the twin roll casted and ingot processed sheets show the fine equiaxed grains with around 9 μm in mean diameter. The twin roll casted magnesium alloy sheet shows superior tensile strength and low elongation compared to the ingot cast one. The results of this work suggest that asymmetric rolling can improve the formability of magnesium alloy and the technique could be extended to enhance the sheet qualities of different alloys in jewelry industry.

Effect of Warm Rolling on Microstructure and Mechanical Properties of Twin-roll Casted ZK60 Alloy Sheets

In this study, ZK60 magnesium alloy strips were produced by twin roll casting (TRC) and then subjected to warm rolling at the temperature of 300 °C and 350 °C. Rolled sheets related to different rolling reductions were prepared after sequential warm rolling with the rolling speed of 5 m/min. Microstructures, texture, hardness, tensile properties of the rolled sheets with different rolling reductions were studied experimentally. It has been found that grain refinement occurs actively during the warm rolling. Also, high density of shear bands were observed in the rolled sheets. The warm rolling sheet presents strong (0002) basal texture. In addition, the increase of the rolling reduction results in the improvement of the mechanical properties.

Differential speed rolling of twin-roll-cast 6xxx al alloy strips and its influence on the sheet formability

We demonstrate the feasibility of a technique that combines twin-roll strip casting, asymmetric rolling, and subsequent heat treatment, in obtaining Al alloy sheets with high-strength/high-formability. The precipitation- hardening Al alloy sheet thus obtained exhibited an excellent formability (