Evolução microestrutural da liga de magnésio MRI 230D submetida a diferentes rotas de processamento em estado semissólido: SIMA e Reofundição
Microstructural evolution of the magnesium alloy MRI 230D submitted to different processing routes in a semisolid state: SIMA and Rheocast
Igor Zimpel, Caroline Almeida Santos Fraga, Sergio Luiz Telles Bartex, Vinicius Karlinski de Barcellos
Resumo
O processamento em estado semissólido visa obter uma microestrutura com grãos globulares, refinados e com propriedades isotrópicas, que tende a apresentar melhores propriedades mecânicas que a morfologia bruta de fusão. A liga de magnésio MRI 230D (Mg–Al6,45–Ca2,25–Mn0,27–Sr0,25–Sn0,84), de alta resistência à fluência, foi submetida a diferentes rotas de processamento em estado semissólido, SIMA (Strain Induced Melt Activation) e Reofundição, com o objetivo de avaliar a influência dos processos na microestrutura da liga. Para a rota SIMA a liga foi previamente laminada, em passe único com deformação de 8%, na temperatura de 250 °C. Posteriormente, a liga foi tratada termicamente nas temperaturas de 540 °C e 570 °C, nos tempos de 40 e 60 minutos. Na reofundição o material foi fundido a 660 °C e lentamente resfriado até a temperatura de processamento (595 °C), e então agitado mecanicamente. Os tempos de agitação variaram de 0 (sem agitação), 1, 2, 4 e 8 minutos. Os resfriamentos, em ambos os processos, foram realizados por imersão em água (25 °C). As amostras foram analisadas por microscopia óptica e eletrônica para avaliação da microestrutura, assim como analisadas termicamente. Os resultados mostraram a formação de grãos com maior fator de forma no processo SIMA além de uma morfologia mais grosseira e homogênea do que pelo processo de reofundição.
Palavras-chave
Abstract
Processing in a semisolid state aims to obtain a microstructure with globular, refined grains and isotropic properties, which tends to present better mechanical properties than as cast morphology. The magnesium alloy MRI 230D (Mg–Al6.45– Ca2.25–Mn0.27–Sr0.25–Sn0.84) was submitted to different processing routes in a semi-solid state, SIMA (Strain Induced Melt Activation) and Rheocasting, to evaluate the influence of these processes on the alloy microstructure. For the SIMA route, the alloy was previously laminated, in single pass with 8% deformation, at the temperature of 250 °C. Subsequently, it was heat treated at different temperatures (540 °C and 570 °C) over 40 and 60 minutes. In the rheocasting process, the material was melted at 660 °C and slowly cooled down to the processing temperature (595 °C) and then mechanically stirred. The mechanical stirring times varied from 0 (without stirring), 1, 2, 4 and 8 minutes. Cooling was performed by immersion in water (25 °C) in both processes. The samples were analyzed by optical and electronic microscopy to evaluate the microstructure, as well as thermally analyzed. The results showed that the SIMA process reach a superior shape factor, in addition to a coarser and homogeneous morphology than rheocasting.
Keywords
Referências
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Submetido em:
06/05/2021
Aceito em:
24/09/2022
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