Papers by Author: Hai Ou Jin

Abstract: The through-thickness textures of different variants of AA6111 T4 sheets were investigated by using X-ray pole figure technique, scanning electron microscopy (SEM), and electron back scattering diffraction (EBSD) technique in SEM. The roping behaviors of the sheets were determined and corelated to the through-thickness texture inhomogeneity. It has been demonstrated that (i) roping is due to through-thickness texture inhomogeneity, (ii) roping occurs in AA6111 when the cube and Goss texture components segregate along the rolling direction (RD) and alternate in the transverse direction (TD), (iii) the texture alignment from sheet surface to 1/5 thickness is most critical to roping behavior, while the effect of texture in the sheet centre is masked by the surface layer, and (iv) the texture alignment can be attributed to the stability of cube and Goss in rolling, and the nucleation and grain growth advantage of cube and Goss during heat treatments.

Abstract: This study examines the recovery behaviour of the inter-alloy region between a core AA6XXX clad with AA3003 after 72% rolling reduction. Sample coupons were heated isochronally or isothermally, at different temperatures or times, respectively, to probe the recovery kinetics of x-ray peak broadening, x-ray macro-texture, and micro-hardness from the cold rolled state. The inter-alloy region had a strong β-fibre typical of rolled Al. The recovery of the {220} and {311} x-ray line profiles were observed between anneals. The full width half maximum was determined from a pseudo-Voigt fit of the profiles to obtain the defect-related information. Distinct changes in the peak shape and microhardness were observed above 80°C (start of recovery), which goes on all the way to 300°C due to recovery, and beyond 300°C both hardness and peak width drop rapidly (recrystallization start), the latter behaviour being closer to AA3004. Modified Williamson-Hall analysis confirms that recovery is due to dislocation annihilation.

Abstract: Two AA5754 sheets have been processed by cold rolling with 83% thickness reduction, one at room temperature and another with liquid nitrogen as coolant. The sheets were subsequently annealed at 220-275°C for 1 hour. The development of grain structure and texture was studied by optical microscope, scanning electron microscopy (SEM), X-ray diffraction and electron backscatter diffraction (EBSD) in SEM, and the mechanical property by micro-hardness testing. It has been demonstrated that the as-rolled sheets have the same micro-hardness, but the grain structures and textures are very different. Compared to the sheet processed with liquid nitrogen, the one rolled at room temperature has stronger shear texture and finer grain structure.

Abstract: A nominally pure Al slab was thermo-mechanically treated to result in a near random texture of 90 m grain size. Subsequent cold rolling with intermediate anneals at 230, 275, and 300°C reduced the Fe solute to near equilibrium compositions below 0.5 ppm atomic. The final cold rolled sheet continuously recrystallized; grain growth of this structure is reported. A grain-growth kinetics mapping was generated, correlating the parameters of Fe-in-Al solubility limit, Fe diffusivities in the grain boundaries and the Al lattice and the activation energies for migration rates.

Abstract: The development of grain structures after asymmetric rolling (ASR) and annealing was investigated in Al-Mg alloys AA5754, AA5182 and AA5083. It has been demonstrated that a fine grain structure could be produced through continuous recrystallization, but it is strongly affected by the presence of large second phase particles. In AA5754 the volume fraction of large particles is relatively low and continuous recrystallization is able to occur throughout the sheet thickness, resulting in a fine grain structure of 2μm mean grain size. In AA5182 the fraction of large particles increases to a level that the continuous recrystallization occurs only in the sheet surface, whereas the sheet centre undergoes discontinuous recrystallization. The discontinuous recrystallization due to particle stimulated nucleation (PSN) is dominant in AA5083 so that no continuous recrystallization has been observed. The fully recrystallized grain structure is slightly finer in the ASR processed AA5083 than the conventionally rolled one.

Abstract: AA5754 sheet has been processed by asymmetric rolling and the development of grain structure and texture in subsequent annealing studied at 240-500°C. It has been found that asymmetric rolling facilitates the formation of ultra-fine grain structure (1-2µm grain size) by shear strain promoted continuous recrystallization, which is a process of extended recovery and subgrain/grain growth. The ultra-fine grain structure is not thermally stable, and when the annealing temperature or time increases, the grain size eventually grows to its Zener limit. The deformation texture is similar to the typical f.c.c. cold rolling texture but rotated about the transverse direction. Along with the formation of an ultra-fine grain structure and subsequent grain growth, the deformation texture is retained.