Electrochemical studies of copper-aluminum-silver alloys in 0.5 M H2SO4

The electrochemical behavior in 0.5 M H2SO4 at 25 degreesC of a Cu-Al(9.3 wt%)-Ag(4.7 wt%) alloy submitted to different heat treatments and an annealed Cu- Al(9.7 wt%)-Ag(34.2 wt%) were studied by means of open circuit potential (E-mix) measurements, potentiodynamic polarizations and cyclic voltammetry. SEM and EDX microanalysis were used to examine the changes caused by the electrochemical perturbations. The steady state potentials observed for the studied samples were correlated in terms of the phases present in the alloys surface. The resulting E/I potentiodynamic profiles were explained in terms of the potentiodynamic behavior of pure copper and pure silver. The presence of aluminum decreased the extent of copper oxidation. In the apparent Tafel potential region, two anodic Tafel slopes were obtained: 40 mV dec(-1) in the low potential region and 130 mV dec(-1) in the high potential region, which were related with the electrochemical processes involving copper oxidation. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Coating residual stress effects on fatigue performance of 7050-T7451 aluminum alloy

The tendency of the aircraft industry is to enhance customer value by improving performance and reducing environmental impact. In view of availability, aluminum alloys have a historically tendency to faster insertion due to their lower manufacturing and operated production infrastructure. In landing gear components, wear and corrosion control of many components is accomplished by surface treatments of chrome electroplating on steel or anodizing of aluminum. One of the most interesting environmentally safer and cleaner alternatives for the replacement of hard chrome plating or anodizing is tungsten carbide thermal spray coating, applied by the high velocity oxy fuel (HVOF) process. However, it was observed that residual stresses originating from these coatings reduce the fatigue strength of a component.An effective process as shot peening treatment, considered to improve the fatigue strength, pushes the crack sources beneath the surface in most of medium and high cycle cases, due to the compressive residual stress field induced. The objective of this research is to evaluate a tungsten carbide cobalt (WC-Co) coating applied by the high velocity oxy fuel (HVOF) process, used to replace anodizing. Anodic films were grown on 7050-T7451 aluminum alloy by sulfuric acid anodizing, chromic acid anodizing and hard anodizing. The influence on axial fatigue strength of anodic films grown on the aluminum alloy surface is to degrade the stress-life performance of the base material. Three groups of specimens were prepared and tested in axial fatigue to obtain S-N curves: base material, base material coated by HVOF and base material shot peened and coated.Experimental results revealed increase in the fatigue strength of Al 7050-T7451 alloy associated with the WC 17% Co coating. on the other hand, a reduction in fatigue life occurred in the shot peened and coated condition. Scanning electron microscopy technique and optical microscopy were used to observe crack origin sites, thickness and coating/substrate adhesion. (c) 2007 Elsevier B.V. All rights reserved.

Friction and wear properties of functionally graded aluminum matrix composites

Aluminum matrix composites are currently considered as promising materials for tribological applications in the automotive, aircraft and aerospace industries due to their great advantage of a high strength-to-weight ratio. A superior combination of surface and bulk mechanical properties can be attained if these composites are processed as functionally graded materials (FGM's). In this work, homogeneous aluminum based matrix composite, cast by gravity, and aluminum composites with functionally graded properties, obtained by centrifugal cast, are tested against nodular cast iron in a pin-on-disc tribometer. Three different volume fractions of SiC reinforcing particles in each FGM were considered in order to evaluate their friction and wear properties. The sliding experiments were conducted without lubrication, at room temperature, under a normal load of 5 N and constant sliding speed of 0.5 ms-1. The worn surfaces as well as the wear debris were characterized by SEM/EDS and by atomic force microscopy (AFM). The friction coefficient revealed a slightly decrease (from 0.60 to 0.50) when FGM's are involved in the contact instead of the homogeneous composite. Relatively low values of the wear coefficient were obtained for functionally graded aluminum matrix composites (≈10-6 mm3N-1 m-1), which exhibited superior wear resistance than the homogeneous composite and the opposing cast iron surface. Characterization of worn surfaces indicated that the combined effect of reinforcing particles as load bearing elements and the formation of protective adherent iron-rich tribolayers has a decisive role on the friction and wear properties of aluminum matrix composites.

A review on the development and properties of continuous fiber/epoxy/aluminum hybrid composites for aircraft structures

Weight reduction and improved damage tolerance characteristics were the prime drivers to develop new family of materials for the aerospace/ aeronautical industry. Aiming this objective, a new lightweight Fiber/ Metal Laminate (FML) has been developed. The combination of metal and polymer composite laminates can create a synergistic effect on many properties. The mechanical properties of FML shows improvements over the properties of both aluminum alloys and composite materials individually. Due to their excellent properties, FML are being used as fuselage skin structures of the next generation commercial aircrafts. One of the advantages of FML when compared with conventional carbon fiber/epoxy composites is the low moisture absorption. The moisture absorption in FML composites is slower when compared with polymer composites, even under the relatively harsh conditions, due to the barrier of the aluminum outer layers. Due to this favorable atmosphere, recently big companies such as EMBRAER, Aerospatiale, Boing, Airbus, and so one, starting to work with this kind of materials as an alternative to save money and to guarantee the security of their aircrafts.

Mechanical and microstructural characterization of laser-welded joints of 6013-T4 aluminum alloy

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

Avaliação do comportamento em fadiga de juntas estruturais de ligas de Al2024T3 coladas com adesivo epóxi

Ligas de alumínio são extensamente usadas em partes aeronáuticas devido às boas propriedades mecânicas e baixa densidade. Estas partes devem ser unidas para formar conjuntos maiores. Uma junta estrutural é definida como um segmento de estrutura que provê um meio de transferir carga de um elemento estrutural para outro. A maioria das juntas aeronáuticas é mecanicamente fixada com múltiplos prendedores (parafusos ou rebites). Estas juntas apresentam uma alta concentração de tensões ao redor do prendedor, porque a transferência de carga entre elementos da junta acontece em uma fração da área disponível. Por outro lado, as cargas aplicadas em juntas adesivas são distribuídas sobre toda a área colada e reduz os pontos de concentração de tensão. Juntas são a fonte mais comum de falhas estruturais em aeronaves e quase todos os reparos envolvem juntas. Portanto, é importante entender todos os aspectos de projeto e análise de juntas. O objetivo deste trabalho é comparar estaticamente juntas estruturais de ligas de Al2024-T3 em três condições: juntas mecanicamente rebitadas, juntas coladas e uma configuração híbrida rebitada e colada. Foi usada a norma NASM 1312-4 para confecção dos corpos-de-prova. Além disso, foram conduzidos testes de fadiga, sob amplitude de carregamento constante e razão de tensão igual a 0,1 para avaliar a eficiência dos elementos estruturais durante sua vida em serviço. Os resultados mostraram que a configuração híbrida apresenta maior resistência estática e uma vida em fadiga superior à configuração colada.

Fractography analysis and fatigue strength of carbon fiber/RTM6 laminates

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Fatigue fracture behavior of Ti-6Al-4V PVD coated

Fatigue, corrosion and wear resistance are important parameters in aircraft components development as landing gear. High strength/weight ratio and effective corrosion resistance make of titanium alloys an alternative choice to replace steel and aluminum alloys. However, titanium alloys have poor tribological properties, which reduce devices performance under friction. PVD coatings tribological systems has been increased due to their attractive mechanical properties as low environmental impact, low friction coefficient, low wear rate and hardness up to 2000 HV.In this study the influence of TiN deposited by PVD on the fatigue strength of Ti-6Al-4V alloy was evaluated. Comparison of fatigue strength of coated specimens and base material shows also a decrease when parts are coated. It was observed that the influence is more significant in high cycle fatigue tests. Scanning electron microscopy technique (SEM) was used to observe crack origin sites and fracture features. (C) 2010 Published by Elsevier Ltd.

Morphological analysis of pits formed on Al 2024-T3 in chloride aqueous solution

It has been used a new image analysis method, based on segmentation by shape parameters, for pits morphology examination from Al 2024 aluminum-copper alloy in chloride aqueous solution. Corrosion behavior of this alloys in naturally aerated 3.5% NaCl solution has been investigated through open circuit potential measurements. Afterwards, pits have been characterized by image analysis taking density and size measurements right from corroded surfaces. Morphological investigation has been conducted for profiles, cut orthogonally from mean surface planes, and observed through light microscopy. Image analysis data could demonstrate that pits are wider than deep, evoluting for conical, quasi-conical or irregular shapes. Most pits have presented a quasi-conical morphology, but the wider ones have evoluted to an irregular shape influenced by sub-surface microstructure. Image analysis based on shape segmentation could enhance the differences on morphological behavior. (C) 2004 Elsevier B.V. All rights reserved.

An image processing method for morphology characterization and pitting corrosion evaluation

A digital image processing and analysis method has been developed to classify shape and evaluate size and morphology parameters of corrosion pits. This method seems to be effective to analyze surfaces with low or high degree of pitting formation. Theoretical geometry data have been compared against experimental data obtained for titanium and aluminum alloys subjected to different corrosion tests. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Um estudo sobre a corrosão aquosa de ligas de alumínio 7xxx submetidas a diferentes tratamentos térmicos

This job aim has been to study the aqueous corrosion of the 7xxx heattreatable aluminium alloys, used in the aeronautical industry. The 7010, 7050 and 7475 alloys, have been supplied in the T7 condition and submitted to the annealed and aging thermal treatments of in order to study their behaviours front to corrosion in 5% NaCl pH 6,0, air-saturated and deaerated solutions. The electrochemical study has been accomplished through potential measures in open circuit, potentiodynamic polarisation curves and electrochemical impedance spectroscopy (EIS). The aged alloy resulted to be the most resistant to corrosion and annealed the less resistant ones. In spite of it they have different chemical compositions, in each mean, the alloy with the same thermal treatment has behaved in a similar way. In aerated solution, the process is controlled by oxygen diffusion and in oxygen absence for dissolution through a film. Hardness and mass loss measures, after corrosion test, have supported this research.

Efeito do nitrato e nitrito na corrosão das ligas de alumínio 2024 e 7050 em soluções de NaCl

The 2024-T3 and 7050-T7 aluminium alloys electrochemical behavior has been studied in NaCl 5% neutral solutions and 0,1M concentration containing NO 3 - or NO 2 -. The current job supports corrosion research on aluminium alloys used in aeronautic industry. Open circuit potential, polarisation curves and electrochemical impedance spectroscopy techniques have been used. In chloride solutions, alloys corrosion takes place through a pitting mechanism. Added anions to aerated solutions do not possess inhibition effect. In deaerated solutions, nitrite has diminished anodic dissolution rate, probably by incorporating this anion in the oxide and/or hydroxide film.

Phase transformations in the Cu-Al alloy with Ag addition

The effect of Ag addition on the phase transformations that occur in the Cu-10% Al alloy was studied using differential thermal analysis, scanning electron and optical microscopies and energy dispersive X-ray analysis. The results indicated that Ag addition is responsible for the separation of the reverse martensitic transformation in two stages, and for the refinement of the α-phase grains. The relative amount of the β1 martensitic phase, retained on slow cooling (above 2 K min-1 of cooling rate), and the relative fraction of phase α2 are increased. The solubility limit of Ag in the matrix is close to 6 mass% and at this concentration the maximum stability of the β-phase is reached. © 2005 Akadémiai Kiadó, Budapest.

Influence of chromate, molybdate and tungstate on pit formation in chloride medium

It has been characterized and evaluated the 2024-T351 and 7050-T7451 aluminum alloys pitting corrosion in naturally aerated chloride aqueous solutions containing chromate, molybdate and tungstate. It has been carried out electrochemical and non-electrochemical immersion corrosion tests accompanied by surface metallography analysis using an optical microscopy. Chromate for the two alloys and in molybdate for 7050 has corrosion inhibiting effects, whereas tungstate promotes the pitting corrosion for these alloys. Quantitative surface analysis upon the alloys after immersion has indicated that pits are predominantly conical or quasi-conical and irregular. In general, pits have been wider than deep and the widest have been also the deepest. Despite inhibitor presence, when pits have been nucleated, they grow with the same intensity. © 2005 Elsevier B.V. All rights reserved.