The directional solidification technique allows the study of growth of the solid phase, as-cast structure and, finally, its mechanical characteristics as a consequence of thermal parameters. On the other hand, in the last decade, a process called equal-channel angular pressing (ECAP) has emerged as a widely-known technique in fabrication of ultrafine-grained metals and alloys. Applicability of the ECAP technique affords an excellent potential for changing, in a controlled and beneficial manner, the resulting properties of metals and alloys. For this paper, an experimental research has been conducted to study the effects of solidification parameter (cooling rate) on resulting microhardness in hypoeutectic Al-Si alloys, upon use of an ECAP procedure. The influence of cooling on the scale of the dendritic patterns is presented and discussed with recourse to equations. The resulting microhardness variation with position throughout the as-cast materials and cooling rate were characterized by experimental power laws. Results determined after the solidification experiments have revealed microhardness as a function of both cooling rate and position (P) of the as-cast materials to be dependent on alloy composition. In the ECAP process via route C with three passes, "as-solidified" microstructures have been found to be distorted and fragmented during the severe plastic deformation. This deformation imposed on the billets during the ECAP process facilitated obtaining a fine microstructure and high levels of microhardness were observed. However, even with the ECAP process, it was shown that microhardness is strongly dependent of the cooling rates.

Um violão é construído essencialmente de madeira. Porém, cada madeira traz consigo algumas características específicas. O seu comportamento acústico está relacionado às propriedades elásticas dos materiais que o compõem. Sabe-se que as propriedades elásticas dos materiais interferem não apenas em sua resistência mecânica, mas também em seu comportamento dinâmico; uma estrutura pode vibrar de forma mais ou menos intensa dependendo do material que a compõe e de suas propriedades elásticas. O presente trabalho analisa o comportamento dinâmico de um modelo computacional de violão através de análises modais calculadas pelo método de elementos finitos (MEF) aplicando condições de contorno que simulam a rigidez das faixas laterais e a tensão das cordas no cavalete e braço obtendo respostas em termos de frequências naturais e as correspondentes formas dos modos de vibração. E assim, comparar com respostas em frequência obtidas experimentalmente através do método de excitação por impulso. Os resultados mostram que as respostas em frequências naturais numéricas se assemelham com os valores obtidos experimentalmente, indicativo de pertencerem a um mesmo modo de vibração.

A comparative analysis was carried out of the alloys examined, using the results found for thermal variables, macrostructure, dendrite arm spacing, modulus of elasticity and microhardness. Comparing all the results for variables, a predominance was found of higher values for the Al-5.0 wt.% Cu alloy in relation to those for the Al-5.0 wt.% Ni alloy. Although structural transition has occurred in both alloys, the columnar–equiaxed transition position in castings was not altered during the solidification experiments. Addition of Ni solute into pure aluminum favors a significant decrease in tertiary dendrite spacing, while Cu addition leads to a coarser microstructure. Primary dendrite arm spacing, also, was measured along the castings of both alloys. Theoretical approaches such as the well-known Hunt–Lu, Bouchard–Kirkaldy, and Kurz–Fisher models were used to determine quantitatively this particular microstructural parameter. Good agreement was observed between experimental data and predictions by Hunt–Lu and Bouchard–Kirkaldy models, which assume solidification under a transient heat-flow condition. Finally, empirical equations relating tertiary dendritic arm spacing and mechanical properties to the scale of the dendritic microstructure have been proposed. While no relationship was observed between modulus of elasticity and tertiary dendritic arm spacing, addition of Cu into pure aluminum as an alloying element favored a reduction in the average value of modulus of elasticity when compared with those observed for the Al–Ni alloy. It was found that the microhardness decreases with increasing tertiary dendritic arm spacings. On the other hand, solute addition of Cu into commercially pure aluminum favors a microhardness higher than that verified during upward unidirectional solidification of the Al-5.0 wt.% Ni alloy.