Estudo da microestrutura, da textura cristalográfica e da recristalização em chapas obtidas por lingotamento contínuo e semicontínuo da liga de alumínio AA4006.

Abstract

AA4006 Aluminum alloy is extensively used in industry. It belongs to the Al-Fe-Si system, with Si between 0,8 and 1,2 % mass, and Fe between 0,5 and 0,8 % mass. This alloy is less studied despite its extensive use. A comparative microstructural study has been performed in as-received AA4006 alloy strip produced by two industrial casting processes: twin roll caster (TRC) and direct chill (DC). Polarized optical microscopy, scanning electron microscopy with microanalysis, electrical conductivity measurements and Brinnel hardness tests have been used for microstructural characterization. Significant differences in the grain and intermetallic particle sizes, morphologies and distributions were detected and are discussed. Thermal treatments effects on the silicon content in solid solution were also studied. Crystallographic textures have been also determined. Textures across thickness of both sheets have been analyzed and compared. Results showed significant texture changes across thickness of the specimens. Texture analysis was carried out using X-ray diffraction technique. Twin roll caster (TRC) sheet presented the typical shear texture near the surface, while, in internal regions, the β-fibre was observed. A recrystallization study of cold rolled metallic sheets is very important to obtain softening temperature for the material during annealing. After cold rolling with 70% of reduction in thickness, followed by isochronous heat treatments, the samples of the two sheets produced by TRC and DC presented a 50% recrystallization temperature around 290 ºC and 270 ºC, respectively. Crystallographic texture can change during the metal rolling and recrystallization. These processing steps can optimize the grain orientation distribution in a metal strip to improve, for instance, the stamping process, in order to obtain an aggregated value product. Softening curves were also compared and determined for the two sheets (rolled and annealed) of the AA4006 aluminum alloy produced by twin roll caster TRC and direct chill DC processes. It was detected that the recrystallization of the strip produced by TRC process occurs at a higher temperature than that for the DC process, despite the little differences in their softening curves. Crystallographic texture results, for the sheet samples, were obtained by using X-ray diffraction and electron back scatter diffraction EBSD techniques. These results indicated the shear texture presence on the surface and β fiber at the center of the cold rolled (70% area reduction) sample for the sheet

Recrystallization and crystallographic texture in AA4006 aluminum alloy sheets produced by twin roll caster and direct chill processes

“…It can be observed that the recrystallized grains present a relatively random (for more details see ref. Souza, 2012) crystallographic orientation (because there are a variety of colors in the spectral color coded map). The deformed and recrystallized sheet sample obtained by the DC process presents larger grains than those of the TRC process, possibly, due to the particle dispersion phenomenon, as previously discussed.…”

Avaliação Da Presença De Soluto Em Folhas De Alumínio

“…Souza [9] evidenciou a diferença de temperatura de recristalização, em função dos processos iniciais de fabricação. Através da elaboração de curvas da derivada da taxa de variação da microdureza versos temperatura.…”

Correlação entre microestrutura e comportamento de corrosão em duas ligas do sistema Al-Fe-Si produzidas pelos processos industriais de lingotamento contínuo e semi-contínuo.

“…Tabela 4 -Solubilidade (% massa) dos principais elementos de liga em alumínio, nos sistemas binários (MONDOLFO,1976;POMEAR, 1989 Na Tabela 5, são apresentados os valores de condutividade elétrica obtidos por Souza (2012c), em quatro condições: no estado "como recebido", após 2 horas e 24 horas de tratamento térmico 400 ºC; e após 2 h de tratamento térmico a 550 ºC. …”