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This work deals with the choice of materials, surface finish and parameters to be considered for the design of the production process of so called “smooth-wall” aluminium containers for food packaging. Evaluating the detachment at the metal/lid interface the following parameters have been considered: (i) the Fe amount in the Al alloy, (ii) the effect of lubricant oil, (iii) the surface “shape” of containers in contact with the lid and (iv) the alloy grain structure. Results obtained suggest that the detachments could be reduced if a low iron content alloy is used. Roughness measurements have highlighted that the surface showing S ku > 3 provides a much higher adhesion. Metallographic measurements showed that the use of high iron content alloy results in numerous corrosion spots preventing adhesion between the sealant polymeric film and the aluminium foil. In conclusion: in all over the design of the device a multifactor approach would be adopted: a right combination of alloy composition, “surface shape”, lubricant oil and alloy grains dimension, should be considered to avoid failures. [ABSTRACT FROM AUTHOR]

Due to risk connected to the chromium use, several companies try to find 'true' chromium free products to treat aluminum surfaces. Aim of this work was to evaluate and test some treatment systems for avionics applications, in order to replace standard chromate processes based on CrVI. AA2014-T3 and AA6082-T6 aluminum alloys were subjected to conversion coating processes based on lithium or zirconium salts. Results were compared to those obtained using commercial chromium free products. The electrochemical and corrosion behavior was investigated using the d.c. electrochemical technique and salt spray test (SST). Moreover, in order to be used in some aircraft and aerospace devices, low electrical contact resistance (ECR) is required; these tests were carried out according to a military standard. The results demonstrated that the AA6082-T6 alloy, treated using lithium salts, has passed the SST but did not pass the ECR test. AA2014-T3 alloy treated using lithium salts has passed neither the SST nor the low electrical resistance test. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The corrosion behavior of bare and chromate–phosphate treated aluminum alloys 8006 and 8079, employed for the production of heat exchangers, was investigated in aqueous aerated 3.5% NaCl solution using electrochemical impedance spectroscopy (EIS). Experimental results indicate that bare 8079 alloy is less sensitive to corrosion in NaCl containing environments than bare 8006 alloy. This behavior was attributed to the lower content of metallic segregates in the 8079 alloy. For the bare samples, the chromate–phosphate treatment improves the corrosion resistance of both alloys; nevertheless their behavior is still dominated by alloy composition. The application of a polymeric coating, ranging from 5 to 7 μm, provided improved protection for the foils investigated during this study. The reliability of these coatings is however dominated by the application procedure and curing. [Copyright &y& Elsevier]

The corrosion behaviour of magnesium in chloride-containing aqueous environment was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) performed simultaneously with real-time hydrogen evolution measurements and optical imaging of the corroding surface. The potentiodynamic investigation revealed substantial deviations from linearity in close proximity of the corrosion potential. In particular, differences in the slope of the current/potential curves were observed for small polarizations above or below the corrosion potential. These observations, suggest that the usual method based on the use of the Stern–Geary equation to convert a value of resistance into a value of corrosion current is inadequate. Nonetheless, a very good correlation between values of resistances estimated by EIS and corrosion currents obtained from real-time hydrogen measurement was found. Real-time hydrogen measurement also enabled, for the first time, direct measurement of an ‘apparent’ Stern–Geary coefficient for magnesium. In order to rationalize the complex behaviours experimentally observed, an electrical model for the corroding magnesium surface is presented. [ABSTRACT FROM AUTHOR]

In this study, the corrosion behaviour of annealed and not annealed AISI 444 ferritic stainless steel in tap water with and without addition of selected concentrations of chloride ions was investigated. Cyclic potentiodynamic macro (large area) and micro (small area) polarization measurements (CPP), salt spray test, SEM and EDS analysis were employed to evaluate the pitting and crevice corrosion susceptibility of annealed and not annealed AISI 444. The results obtained indicate that annealing does not improve the resistance to pitting and crevice corrosion. Moreover, micro CPP indicates local susceptibility to pitting on both annealed and not annealed materials; such susceptibility was not evident from macropolarization tests. [ABSTRACT FROM AUTHOR]

Corrosion fatigue is defined as the sequential stages of metal damage that evolve with accumulated load cycling, in an aggressive environment, and resulting from the interaction of irreversible cyclic plastic deformation with localized chemical or electrochemical reactions. It appears then evident the need to know and understand all phenomena that are involved in pit formation and growth in the presence of both an aggressive environment and a cyclic load. Although each single effect of both fatigue and corrosion have been extensively documented for aluminium alloys, their synergic action is not thoroughly understood and it continues to be an area of considerable scientific and industrial interest. Fatigue experiments were conducted on bare AA 2024 T3 aluminium alloy specimens in the presence of an aggressive environment consisting of a water aerated solution with 3.5% of NaCl in weight. The specimen was stressed in a four-point bending test; the upper surface of the specimen, experiencing only tensile stress, was the monitored one. True strain on this surface was monitored by means of fibre optic Bragg grating. The strain and open circuit potential variations observed as a function of number of cycles are interpreted as a result, and taking into account the numerous and complex phenomena occurring as time goes on. The pits birth and their subsequent growth seem to play a significant role in crack initiation and subsequent propagation up to final catastrophic failure. This has been verified also by means of finite element method analysis. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]