Abstract The development of low-cost high quality surface finishing methods for silicon carbide (SiC) is an arduous task. Nowadays, the SiC mirrors manufacture involves extensive, complex, and costly finishing processes carried out on highly expensive ultra-precise machines. In this work, a cost-effective surface finishing method has been successfully developed, using conventional machines for the optical finishing of SiC. The results showed that the combination of ductile grinding and polishing in conventional low-cost machines allowed to obtain high-quality surface finish on SiC substrates with low roughness (4 - 10 nm Ra ) and optical figure in the range λ / 4 - λ / 8, at a reduced 32 hours total processing time.

Grain refinement in Al-Si alloys improves their mechanical properties. Research available in the literature shows the search for refinement efficiency through heterogeneous nucleation of the grain, involving the stoichiometric ratio between the alloy elements, the inoculant, and process parameters. In these surveys, there are divergences of information. However, this study does not aim to contradict this information but present an investigation made with the Al-4Nb-0.5B master alloy, where Nb >> B, used via sticks, with variations from 0 to 1 Wt.% of Nb and B according to a stoichiometric calculation added to the alloys cast with Al (7, 9, 12) Wt.% of Si and 1 Wt.% of Fe. The study also enabled an investigation into the morphology behavior of the β-Fe precipitates arising from Fe-critic in the alloy. Samples cast according to the TP1-2012 mold standard. The alloy microstructure analyzed was by energy-dispersive X-ray spectroscopy. The small addition of Nb-B can efficiently and significantly refine the size of the primary α-Al grain and has caused changes in the morphology of Fe-rich intermetallic, which became very refined spheroidised, suggesting an improvement in the mechanical properties of the material.

Três processos de união de perfis de alumínio concorrem para a manufatura de painéis estruturais (união entre revestimento e reforçadores) aeronáuticos: rebitagem, Friction Stir Welding (FSW) e soldagem a laser (Laser Beam Welding - LBW). Esses processos têm vantagens e desvantagens particulares, as quais foram analisadas no presente estudo focando, especificamente, nas propriedades de tração do conjunto unido. Dois ensaios mecânicos foram considerados, T-pull test e Hoop test. No que tange ao ensaio T-pull, as amostras soldadas por LBW apresentam maior capacidade de suportar cargas. Isso se deve à melhor distribuição de cargas, quando a solicitação mecânica se faz pelo reforçador. No caso do ensaio Hoop, onde a solicitação mecânica se dá exclusivamente no revestimento, os resultados obtidos por FSW são notadamente superiores aos obtidos pelos demais processos, em termos de tensão máxima, tensão de escoamento e de alongamento máximo. Conclui-se que tanto o LBW quanto o FSW são métodos de soldagem com possibilidade de substituir a rebitagem comumente aplicada nas aeronaves comerciais.

Three welding processes for aluminum parts have been considered for the aircraft fabrication: riveting, friction stir welding (FSW) and laser beam welding (LBW). These processes have advantages and threats, which were analyzed in the present work focusing on T-pull and Hoop tensile properties. Concerning T-pull tests, LBW coupons presented higher ability to withstand the applied loads. This was due to the better distribution of loads when the strain is done to the stringer direction. In the case of the Hoop tests, which stress only the skin, the results obtained after FSW were notably higher in terms of ultimate tensile stress, yield stress and maximum strain. It was concluded that both LBW and FSW could replace riveting usually applied for commercial aircraft manufacturing.