Ag-rich precipitates formation in the Cu-11%Al-10%Mn-3%Ag alloy

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Estudo da propagação de trinca por fadiga sob carregamento de amplitude variável

For engineering projects that require high reliability levels, is often not enough know only physical and chemical material properties. It’s necessary understand the failure mode of these materials in operation to ensure security level in the project and establish more stringent criteria in the analysis of structural integrity. Due to this need, aircraft industry has been using aluminum alloys in their designs and projects. “Currently more than 70% of aircraft structures are built of high strength aluminum alloys among which stand out 7075-T6 and 2024-T3 alloys, which are considered basics for being used in the new alloys development.” (PASTOUKHOV & VOORWALD, 1995). Some years ago ALCOA develops Al 2524 alloy that has emerged as refinement of Al 2024 (Al, Cu. Mg) alloy, with purpose of improve fracture toughness and fatigue resistance on structural components. The present research addresses testing of fatigue crack propagation under variable amplitude loading for Al 2024 alloy, observing the interaction effects from application of overhead blocks and plastic zone at the crack tip and makes an analysis of fracture surface images

Estudo do efeito do modificador Al-Sr no tratamento de modificação do eutético da liga AA356

The AA356 alloy is an alloy widely used in the automotive industry and aerospace due to its excellent mechanical properties. Refining the structure of eutectic silicon aluminum alloys is a fairly common practice in the foundry through treatment known as modification. This can be achieved by modifying agent adding chemicals such as contained in groups I and IIa of the periodic table and rare earths (europium, céreioi, praseodymium, neodymium, etc.). Has the ability to modify the structure of the eutectic, but only sodium and strontium produce an action modifier strong when used in low concentrations. The modifying effect of the shafts turn silicon into a fibrous form and branched surrounded by metallic matrix in the form of a composite structure that has the highest limit of tensile strength, ductility and machinability. In this work will be obtained ingots with and without the modifier type Al-10% Sr, made in sand molds and are generated and analyzed cooling curves and also the study of the macrostructure and microstructure of the solidified material. It was found that by adding the Al-Sr made shorten the solidification time and lower the grain size

Efeito do Estrôncio (Sr) no tratamento de modificação do eutético da liga Al-1%Si

This study aimed to analyze the cooling curves, micro and macrograph alloy Al-1 %Si without the addition of strontium modifier and with the addition of the same. One of the ways of improving mechanical properties of alloy Al -Si is through the modification process. For the experiments two billets of the alloy Al-1%Si cast iron mold in a billet with addition of 0.02% strontium by weight, and the other billet without the addition of modifier were fused. In the solidification process of billet temperature was monitored and recorded every second for later plotting in Origin 8 program and analyzes the cooling curves obtained. The billets were cut and passed by grinding and polishing to perform the macrograph and micrographs. The results concerning the macrograph indicated that billet without the addition of Strontium particle size obtained was more refined than the billet where the strontium modifier was added. Regarding the micrograph, photos stemmed from the optical microscope didn´t show the expected modification effect by the addition of Strontium. This suggests that the low amount of silicon (1 %) present in the alloy used in this study interfered in the change process, because according to the literature review, Strontium 0.022 % by weight is sufficient to fully modify an alloy with 7% Silicon. The results from the cooling curve showed that both the eutectic temperature and the solidification time remained unchanged with the addition of strontium

Caracterização estrutural da Liga Al-1% Si

The aim of this study is to characterize the macrostructure and microstructure of Al - 1%Si alloy obtained in sand and metallic molds. Aluminium has good mechanical properties, but adding silicon, even in small quantities, can change the microstructure and improves mechanical behavior. Workpieces were castings in metallic and sand molds and one can see a difference in their cooling curve, macroscopic and microscopic structures. The sand mold casting has lower cooling rate and so its grains are larger. Due to the lower concentration of grain boundary, the hardness is lower compared to that found in metallic molds, which has smaller grains and a higher hardness. Therefore, it can be concluded that the cooling rate and alloying elements affect the final microstructure of the workpiece

Análise da pulsação térmica do processo TIG na soldagem da liga AA6063T6

Pós-graduação em Engenharia Mecânica - FEB

O trabalho rural e a sazonalidade do café: um estudo sobre assalariados do município de Campo Belo - MG

Pós-graduação em Serviço Social - FCHS

Streptococcus mutans adhesion and releasing of metallic ions in dental alloys

AIM: To evaluate the adherence of Streptococcus mutans to the surface of the amalgam and copper/aluminum alloy samples and also evaluate the release of metallic ions. METHODS: The prepared medium was changed every 72 h and analyzed by atomic absorption spectrophotometer. Samples were removed from the prepared medium at 15, 30, 48 and 60 days. RESULTS: The result shows that ions released were statistically different among all groups, and so were both biofilm and pits formation and the corrosion induced by the S. mutans in both types of samples. SEM observation of the samples immersed in the prepared medium with S. mutans showed adherence of microorganisms on the whole surface, in all groups. CONCLUSIONS: The S. mutans adhere to both amalgam and copper/aluminum alloy causing corrosion of those restorations. S. mutans produced a greater ions release in Cu/Al alloy; in amalgam, the ions release was not influenced by exposure to S. mutans.

Ecological strategies of Al-accumulating and non-accumulating functional groups from the cerrado sensu stricto

Coordenação de Aperfei çoamento de Pessoal de Nível Superior (CAPES)

Adsorção-fotodegradação do herbicida paraquate em água pela argila Na-Bentonita e por novos materiais TiO2-Bentonita, TiO2/ZnOBentonita, Al/Fe-Bentonita e Al/Fe.Cu-Bentonita

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Anodization mechanism on SiC nanoparticle reinforced al matrix composites produced by power metallurgy

Specimens of aluminum-based composites reinforced by silicon carbide nanoparticles (Al/SiCnp) produced by powder metallurgy (PM) were anodized under voltage control in tartaric-sulfuric acid (TSA). In this work, the influence of the amount of SiCnp on the film growth during anodizing was investigated. The current density versus time response and the morphology of the porous alumina film formed at the composite surface are compared to those concerning a commercial aluminum alloy (AA1050) anodized under the same conditions. The processing method of the aluminum alloys influences the efficiency of the anodizing process, leading to a lower thicknesses for the unreinforced Al-PM alloy regarding the AA1050. The current density versus time response is strongly dependent on the amount of SiCnp. The current peaks and the steady-state current density recorded at each voltage step increases with the SiCnp volume fraction due to the oxidation of the SiCnp. The formation mechanism of the anodic film on Al/SiCnp composites is different from that occurring in AA1050, partly due the heterogeneous distribution of the reinforcement particles in the metallic matrix, but also to the entrapment of SiCnp in the anodic film.

Electrochemical studies of copper, copper-aluminium and copper-aluminium-silver alloys: Impedance results in 0.5M NaCl

The electrochemical behaviour of Cu, Cu-Al and Cu-Al-Ag alloys in aqueous solutions of NaCl (0.5 M, pH = 3.00) was studied by means of voltammetric methods and electrochemical impedance spectroscopy. The surfaces were examined by SEM and EDX analysis. Cu-Al-Ag alloy shows a potentiodynamic behaviour similar to that of the pure copper electrode while the Cu-Al alloy presents some minor differences. In the active dissolution region the electrodes suffer pitting corrosion and in the other potential regions there are the formation of a passivant film with composition depending on the potential. The impedance responses of the electrodes are discussed. An electrodissolution mechanism is proposed and the effect of the alloying elements upon the impedance response and polarisation curves is explained. The main effects are due to the production of copper and silver chlorides and aluminium oxides/ hydroxides at the corroding interface. The addition of Al or (Al + Ag) increases the corrosion resistance of pure copper. © 1995.

Influence of Mg on the structural and optical properties of LiNbO3 thin films grown by polymeric precursor method

A polymeric precursor solution was used to deposit pure and Mg doped LiNbO3 thin films on sapphire substrates by spin-coating. The effects of magnesium addition on crystallinity, morphology and optical properties of the annealed films were investigated. X-ray diffraction patterns indicate the oriented growth of the films. Phi-scan diffraction evidenced the epitaxial growth with two in-plane variants. AFM studies show that the films are very homogeneous, dense and present smooth surfaces. The refractive index and optical losses obtained by the prism coupling method were influenced by the magnesium addition.

Influencia del nivel de inserción ósea del diente soporte en el desplazamiento de PPR de extremidad libre mandibular asociada al implante oseointegrado

The rehabilitation with mandibular distal extension removable partial dentures (DERPD) is complex and the use of implants has been improving the functioning of this approach. The insertion bony level around of the last support tooth is an aggravating factor, since it can harm the longevity of the treatment. Thus, the aim of this research was to evaluate the displacement tendency of a mandibular DERPD associated to an implant, with different insertion bony levels and different connections between the RPD and the support tooth, by finite element analysis. Eight models were made: MA - DERPD, incisal rest, no bony loss; MB - DERPD, distal plate, no bony loss; MC - DERPD, incisal rest, no bony loss, with implant and ERA system; MD - DERPD, distal plate, no bony loss, with implant and ERA system; ME - DERPD, incisal rest, bony loss; MF - DERPD, distal plate, bony loss; MG - DERPD, incisal rest, bony loss, with implant and ERA system; MH - DERPD, distal plate, bony loss, with implant and ERA system. Loads of 50 N in each peak were applied. Displacement maps were obtained and showed that implant favors this association and the bony loss harms the prognostic of the prosthesis. It is concluded that: the introduction of the implant with ERA system reduced the displacement tendency of the tooth and supporting structures; introduction of distal plate reduced the movement tendency of the support tooth; the decrease of the periodontal support didn't influence significantly the displacement tendency of the models with distal plate distal, but it influenced the models with distal incisal rest.