Correlação entre parâmetros microestruturais e resistência mecânica de uma liga Al-Ni-Co
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2023-07-28
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Universidade Estadual Paulista (Unesp)
Resumo
As ligas de alumínio têm sido um dos principais materiais utilizados em componentes estruturais de
aeronaves devido às suas características já consolidadas em termos de desempenho, métodos de projeto,
fabricação e técnicas de inspeção. As propriedades mecânicas, químicas e elétricas das ligas metálicas
estão diretamente relacionadas ao arranjo microestrutural – este último depende dos elementos de
liga e dos parâmetros de fabricação. Assim, percebe-se a importância de se estudar os parâmetros de
fabricação diretamente com as propriedades requeridas e a falta de referências correlacionando-as. Este
estudo visa desenvolver experimentalmente uma liga Al-2%Ni-0,5%Co para aplicações aeroespaciais,
avaliando os principais aspectos metalúrgicos que influenciam a resistência mecânica. A morfologia
da microestrutura foi avaliada por análise metalográfica empregando microscopia ótica e eletrônica de
varredura, e o comportamento mecânico foram avaliados por meio de ensaios de tração e microdureza
Vickers. As amostras foram solidificadas em moldes de bronze com quatro diâmetros diferentes e em
solidificação direcional vertical ascendente, permitindo diferentes taxas de resfriamento. Uma análise
estatística da correlação entre parâmetros microestruturais e propriedades mecânicas foi proposta para
otimizar as condições para obtenção da melhor resistência mecânica. Foi observada uma microestrutura
com uma matriz essencialmente celular da fase α-Al em moldes de bronze e uma matriz essencialmente
dendrítica da fase α-Al na solidificação direcional vertical ascendente. As propriedades mecânicas
observadas foram valores limite de resistência à tração (σU ) de 100 MPa, limite de escoamento (σe) de
74 MPa, alongamento específico (δ) de 35% e microdureza Vickers média de 32HV. Portanto, vale
ressaltar que houve uma compensação entre a matriz rica em alumínio e as fases que compõem o
eutético (α-Al, Al3Ni e Al9Co2), no sentido de aumentar a resistência média com o aumento da escala
da matriz, o que contraria o previsto pela Teoria Clássica de Hall-Petch. A adição de cobalto à liga
Al-2%Ni contribuiu para aumentar a ductilidade da liga Al-2%Ni, sem prejuízo dos valores de σU , em
comparação com anteriores estudos disponíveis na literatura.
Aluminum alloys have been one of the leading materials used in aircraft structural components due to their already consolidated characteristics in terms of performance, design methods, manufacturing, and inspection techniques. Metallic alloys’ mechanical, chemical, and electrical properties are directly related to the microstructural arrangement—the latter depends on the alloying elements and manufac turing parameters. Based on the statements, one can see the importance of studying the manufacturing parameters directly with the required properties and the lack of references correlating them. This study aims to experimentally develop an Al-2wt.%Ni-0.5wt.%Co alloy for aerospace applications, evaluating the main metallurgical aspects that influence mechanical strength. Microstrucure morphology were evaluated by metallographic analysis employing Optical and Scanning Electron microscopy and the mechanical behavior were evaluated through tensile and Vickers microhardness tests. The samples were solidified in bronze molds with four different diameters and in assembly vertical upward directio nal solidification, allowing different cooling rates. A statistical analysis of the correlation between microstructural parameters and mechanical properties were proposed to optimize the conditions for obtaining the best mechanical strength. A microstructure with an essentially cellular matrix of the α-Al phase was observed in bronze molds and an essentially dendritic matrix of the α-Al phase in the assembly vertical upward directional solidification. The mechanical properties observed was a tensile strength limit values (σU ) of 100 MPa, Yield strength (σe) of 74 MPa, specific elongation (δ) of 35%, and average microhardness of 32HV. Therefore, it is noteworthy that there was a compensation between the matrix rich in aluminum and the phases that compose the eutectic (α-Al, Al3Ni e Al9Co2), in the sense of increasing the average resistance with the increase of the matrix scale, which contradicts what was predicted by the Classical Hall-Petch Theory and the addition of cobalt to the Al-2wt.%Ni alloy contributed to increasing the ductility of the Al-2wt.%Ni alloy, without detriment of σU values, compared with previous studies.
Aluminum alloys have been one of the leading materials used in aircraft structural components due to their already consolidated characteristics in terms of performance, design methods, manufacturing, and inspection techniques. Metallic alloys’ mechanical, chemical, and electrical properties are directly related to the microstructural arrangement—the latter depends on the alloying elements and manufac turing parameters. Based on the statements, one can see the importance of studying the manufacturing parameters directly with the required properties and the lack of references correlating them. This study aims to experimentally develop an Al-2wt.%Ni-0.5wt.%Co alloy for aerospace applications, evaluating the main metallurgical aspects that influence mechanical strength. Microstrucure morphology were evaluated by metallographic analysis employing Optical and Scanning Electron microscopy and the mechanical behavior were evaluated through tensile and Vickers microhardness tests. The samples were solidified in bronze molds with four different diameters and in assembly vertical upward directio nal solidification, allowing different cooling rates. A statistical analysis of the correlation between microstructural parameters and mechanical properties were proposed to optimize the conditions for obtaining the best mechanical strength. A microstructure with an essentially cellular matrix of the α-Al phase was observed in bronze molds and an essentially dendritic matrix of the α-Al phase in the assembly vertical upward directional solidification. The mechanical properties observed was a tensile strength limit values (σU ) of 100 MPa, Yield strength (σe) of 74 MPa, specific elongation (δ) of 35%, and average microhardness of 32HV. Therefore, it is noteworthy that there was a compensation between the matrix rich in aluminum and the phases that compose the eutectic (α-Al, Al3Ni e Al9Co2), in the sense of increasing the average resistance with the increase of the matrix scale, which contradicts what was predicted by the Classical Hall-Petch Theory and the addition of cobalt to the Al-2wt.%Ni alloy contributed to increasing the ductility of the Al-2wt.%Ni alloy, without detriment of σU values, compared with previous studies.
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Palavras-chave
Aeronautica, Confiabilidade (Engenharia), Ligas, Microestrutura, Solidificação