Metals solidification involves the transformation of the molten metal back into the solid state. Solidification structures impact heavily on the final product's characteristics. The microstructure effects on metallic alloys properties have been highlighted in various studies and particularly the dendrite arm spacing influence upon the mechanical properties such as tensile strength has been reported. In the present investigation, Al-10wt%Si-2wt%Cu and Al-10wt%Si-5wt%Cu alloys were directionally solidified upward under transient heat flow conditions. The experimental results include solidification thermal parameters such as tip growth rate and cooling rate, optical microscopy, volume fraction of the eutectic mixture, primary dendritic arm spacing and ultimate tensile strength. Experimental growth laws of primary dendrite arm spacing as a function of the solidification thermal parameters are proposed. The Hall-Petch mathematical expressions were used to correlate the ultimate tensile strength as a function of the primary dendritic arm spacing. It was found that the alloy with higher copper content had a more refined structure. More refined structures had higher ultimate tensile strength values.

RESUMO As condições operacionais impostas nos processos de fundição geram, como consequência direta, uma diversidade de estruturas de solidificação. Em geral, as propriedades mecânicas mostram-se fortemente dependentes da morfologia estrutural e da composição química. Um aço de baixo carbono foi utilizado para promover fluxo de calor unidirecional durante a solidificação e obter o arranjo da microestrutura. O objetivo deste trabalho é pesquisar a influência das variáveis térmicas de solidificação na microestrutura da liga Al-10%Si-2%Cu e na sua resistência mecânica. Resultados experimentais incluem os espaçamentos dendríticos primários (EDP), velocidade de deslocamento da isoterma liquidus (VL), taxa de resfriamento (TR) e limites de resistência à tração (LRT) e de escoamento (LE). Estruturas dendríticas mais grosseiras tendem a diminuir a resistência à tração e ao escoamento na liga em estudo.

ABSTRACT The imposition of a wide range of operational conditions in foundry and castings process generates, as a direct consequence, a diversity of solidification structures. The mechanical properties show to depend strongly on the structural morphology and chemical composition. A low carbon steel mold was used to promote a unidirectional heat flow during solidification and to obtain the arrangement of the microstructure. The aim of the present article is to investigate the effect of thermal solidification variables on the microstructure of the Al-10wt.%Si-2wt.%Cu alloy and its mechanical strength. Experimental results include primary dendrite arm spacings (EDP), tip growth rate (VL), cooling rate (TR) and tensile (LRT) and yield (LE) strength limits. A coarser dendritic structure tends to improve the tensile strength and the yield tensile strength in the studied alloy.

"Mario Schenberg" is a spherical gravitational wave (GW) detector that will be part of a GW detection array of two detectors. Another one is been built in The Netherlands. Spherical gravitational wave detector is a resonant-mass detector, which signal comes when the GW passes through and causes vibrations in a spherical mass. The resonant frequencies of this array will be around 3.2 kHz with a bandwidth of about 200 Hz. This range of frequencies is new in a field where the typical frequencies lay below 1 kHz, making the transducer development some more complex. In this work we made a series of fine element studies in sphere coupled to a resonant mushroom shape resonator that will work as a mechanical impedance matcher between the sphere and the transducer. We describe the search for a shape in the impedance matcher that will improve the performance of the detector.