Jean Paul Chopart

Impedance of Laminar Free Convection and Thermal Convection at a Vertical Electrode

Simultaneous heat and mass transfer under thermal laminar free convection to a vertical electrode was investigated. On the basis of Marchiano and Arvias theory developed in steady state, the ac diffusion impedance for a circular or a rectangular vertical electrode was calculated as a function of frequency. For this calculation, the dimensionless local flux was expressed as a series expansion of the dimensionless local characteristic frequency ξ in the low-frequency range and proportional to ξ +1/2 in the high-frequency range. With 80 terms in the series, the two solutions were shown to overlap fairly well for 1.6 ≤ ξ ≤ 10. The overall impedance was then obtained for the different electrode geometries. For a circular electrode these theoretical predictions were successfully tested with different steady temperature differences, ΔT, between the electrode and the solution (0° ≤ ΔT ≤ 2.65°).

Influence of zinc (II) ion concentration on Ni–Zn–P coatings deposited onto aluminum and their corrosion behavior

Abstract Various Ni–Zn–P alloy coatings were deposited onto aluminum substrates using electroless plating from a sulphate bath containing varying amounts of zinc (II) ions. Different techniques, such as scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction, were employed to characterize the morphology, composition and structural properties of the resulting films. The effect of varying Zn content on the corrosion properties of the coatings was tested in 3 wt.% NaCl media, by means of current–potential curves, potential transients and electrochemical impedance spectroscopy measurements. It was found that increasing ZnSO4 concentration from 5 to 25 g l−1 in the plating bath, increases the Zn content in the film from 9.90 wt.% to 12.7 wt.%, reduces the film thickness, modifies the surface morphology and significantly reduces the corrosion rate.

Stress in Aluminium Alloys Measured Using Göbel Mirror as a Primary Beam Optics of X-Ray Diffractometer

Grazing incidence geometry, called MGID-sin2y, was applied to measure surface stresses in very thin layers (depth of a few mm) of Al-Mg alloy samples subjected to different thermal and mechanical treatments. The Göbel mirror was used to parallelize the incident X-ray beam. Perfect collimation of the beam significantly increases accuracy of determined peak position and consequently allows to measure low stresses in surface layers.

Stress Measurements in Polished Al-Mg Alloy and CrN Coating Using Multireflection Grazing Incidence Method

The multi-reflection grazing incidence X-ray diffrection was used to determine residual stress gradient in the mechanically polished Al-Mg alloy and CrN coating. Also, the root mean square values of the third order lattice strain was determined using Wiliamson-Hall method. The results obtained for Al-Mg alloy show that the stress field in the surface layer as well as the microstructure (density of dislocation) depend strongly on the sample preparation. A very high residual compressive stress, which does not change significantly with depth, was measured in the CrN coating. Moreover, a large value of the measured third order strains in the coating was found.

Sulfuric Containing Sugar Bath and Permanent Weak Magnetic Field Effect during Anodizing AlCu 6 Si Alloy Sheet Surfaces

Rolling and perpendicular to rolling surfaces of AlCu6Si aluminum sheet have been anodized at 27 ± 1°C in 20 wt % sulfuric acid containing an additive of white sugar powder with and without permanent weak magnetic field. After one hour of anodizing, some hillocks-shaped micropores are developed and craters are formed in the oxide layers. The micropores obtained in rolling faces are often smaller than those obtained on other faces. Sulfuric anodizing at 21 V causes the formation of combined micropore-nanopore structures in rolling surface. It demonstrated that sugar additive increases the density of micropores in spherical shape in rolling surface and the increasing of sugar concentration changes the pores to hillocks form. In addition, the application of weak magnetic field induces homogeneous repartition of micropores.

Corrosion behavior on the different zones of AA2014 welded aluminum alloy by AA5554 filler aluminum alloy with TIG process: Before and after solution heat treatments followed by ageing

In this work, we have studied the effects of solution heat treatment followed by ageing on the corrosion behavior of AA2014 aluminum alloy welded by AA5554 aluminum alloy. Two samples are then analyzed, in the first case the solution heat treatment is followed by quenching and natural ageing of 90 days (sample 1), and in the second one, the solution heat treatment is followed by quenching and artificial ageing of twelve hours at 190°C (sample 2). The principal observations can be summarized as: evaporation of magnesium in fusion zone, and diffusion of magnesium and copper from the heat affected zone to the fusion zone were identified. Solution heat treatment, quenching and 90 days of natural ageing leads to a uniform corrosion in the heat affected zone and in the fusion one, when the material is immersed for ten seconds in Keller reagent solution. After immersion in 0.3% NaCl chloride solution, and after solution treatment and quenching, we observed that applied artificial ageing at 190°C causes localized corrosion surrounding precipitates and then develops uniform corrosion in all zones, particularly in the fusion one. Finally, it is noted that the surface of different zones became nobler after applying solution heat treatment followed by natural ageing.