Correlation between Hardness, Structure and Electrochemical Performance of an AlZnMnMg Alloy (original) (raw)
Related papers
Influence of the heat treatment in the electrochemical corrosion of Al-Zn-Mg alloys
Journal of Applied Electrochemistry, 1992
The localized corrosion of A1-(5.03 %)Zn-(l. 67%)Mg-(0.23 %)Cu alloys and high purity A1 has been studied using electrochemical techniques, optical microscopy, SEM and EDX. The samples were previously submitted to different heat treatments in which coherent and incoherent MgZn2 precipitates with different distribution and aggregation degree were produced. The influence of NaC1 and Na2 SO4, dissolved oxygen, immersion time and convection were studied. In NaC1 solutions, pitting potentials for the alloys were more negative than for aluminium, indicating an increase in their susceptibility to localized corrosion. Moreover, annealed and cold-rolled alloys presented more negative pitting and repassivation potentials than those submitted to age hardening with direct or interrupted quenching. In annealed and cold-rolled samples, pit nucleation and propagation takes place in the zones where MgZn 2 is accumulated. In the case of the age-hardened alloys, a double pitting behaviour is observed, the first one in the magnesium and zinc enriched regions and the second in the matrix. While the cold water quenched alloy is susceptible to stress corrosion cracking, the alloy submitted to the interrupted quenching process is less susceptible to intergranular attack. The sulphate ion shifts the pitting potential of aluminium and the alloys by chloride towards more positive values because it impedes local accumulations of the latter.
Electrochemical behaviour of heat-treated AlZnMg alloys in chloride solutions containing sulphate
Electrochimica Acta, 2002
The electrochemical corrosion and passivation of AlÃ/5ZnÃ/1.7MgÃ/0.23Cu Ã/0.053Nb alloys, submitted to different heat treatments (cold-rolled, annealed, quenched and aged, and quenched in two steps and aged), in sulphate-containing chloride solutions, has been studied by means of cyclic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS). The cyclic polarization curves showed that sulphate addition to the chloride solution produced a poor reproducible shift of the breakdown potential to more positive potentials. The repassivation potentials, much more reproducible, and practically separating the passive from the pitting potential region, were slightly displaced in the negative direction with that addition. When the alloys were potentiodynamically polarized in the passive potential region, sulphate was incorporated in the oxide film, thus precluding chloride ingress. In addition, Zn depletion was favoured, whereas Mg losses were avoided. Different equivalent circuits corresponding to different alloys and potentials in the passive and pitting regions were employed to account for the electrochemical processes taking place in each condition. This work shows that sulphate makes these alloys more sensitive to corrosion, increasing the fracture properties of the surface layer and favouring the pitting attack over greater areas than chloride alone. #
Effect of Different Media on the Corrosion Behavior and Some Mechanical Properties of Al-Zn-Mg Alloy
Engineering and Technology Journal, 2010
This work investigates the effect of different media (0.1N of NaOH, H2SO4 and NaCl solution) on the polarization behavior of Al-Zn-Mg alloy and calculates some of the corrosion parameters such as corrosion potential (Ecorr) and current density (icorr), cathodic and anodic Tafel slopes (bc & ba), and the polarization resistance (Rp) . The results of the polarization resistance indicates that Al-Zn-Mg alloy have resistance in slat solution higher than that observed in acidic and basic solution respectively . Also some of the mechanical properties like the hardness and wear were measured. The results for hardness showed that the untreated alloy in the experimental solutions had higher hardness than those which are treated in salt, acidic , and basic solutions respectively . While the results for the rate of wear at different sliding speeds showed that the rate of wear for the samples that treated in basic solution higher than those for samples which are treated in the acidic and salt s...
Structure and corrosion resistance of aluminium AlMg2.5; AlMg5Mn and AlZn5Mg1 alloys
Purpose: The aim of the work was the evaluation of corrosion resistance and structure of aluminium AlMg2.5; AlMg5Mn and AlZn5Mg1 alloys.Design/methodology/approach: The corrosion resistance tests of investigated alloys were carried out by means of potentiodynamic method registering anodic polarization curves in 3.5% NaCl solution at room temperature. Registering anodic polarization curves was conducted at the potential rate equal to 1mV/s. As the reference electrode was used saturated calomel electrode (SCE) and the auxiliary electrode was platinum electrode. Mechanical properties were evaluated on the basis of Vickers hardness test. The test was realized with the use of Hauser hardness tester. The observations of the surface morphology after corrosive tests were carried out using Digital Scanning Electron Microscope DSM 940 OPTON.Findings: The investigations of corrosion resistance of examined aluminium alloys shows that the highest corrosion resistance in 3.5% NaCl solution was ob...
Comparative study on corrosion behaviors of Mg-Al-Zn alloys
Transactions of Nonferrous Metals Society of China, 2018
A comparative study on corrosion behaviors of various Mg−Al−Zn alloys (AZ21, AZ41, AZ61 and AZ91 series, cast under same cooling conditions and controlled alloying composition) was carried out. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used for microstructural examinations. The corrosion behaviors were evaluated by immersion tests and potentiodynamic polarization measurements in 3.5% NaCl solution. The results showed that the influence of Al addition on corrosion resistance was more pronounced up to 4% (i.e. AZ41) above which its influence was at less extent. The deterioration of the corrosion resistance of the alloys, at higher Al contents, was attributed to the amount and morphology of β-Mg 17 Al 12 intermetallics and the interruption of continuity of the oxide film on the surface of the alloys owing to coarsened β intermetallics.
The effect of heat treatment on the structure and corrosion resistance of Al-Zn-Mg alloys
Polish Maritime Research, 2008
The effect of heat treatment on the structure and corrosion resistance of Al-Zn-Mg alloys The parameters of heat treatment of Al-Zn-Mg alloys subjected to precipitation hardening have a substantial impact on mechanical and corrosion resistance. The rate of cooling after supersaturation, along with the ageing temperature and time, affect significantly mechanical properties of these alloys. The type of ageing (artificial or natural) after saturation implies corrosion resistance in seawater. Being a modification of the AlZn5Mg1 alloy, denoted as PA47, the AlZn5Mg2CrZr alloy reveals best mechanical properties among all aluminium alloys in shipbuilding [1]. However, the higher level of precipitation hardening, the higher susceptibility to corrosion, in particular to stress corrosion cracking (SCC). Describing the structure of Al-Zn-Mg alloys by identifying the precipitation free zone (PFZ) and the Guinier-Preston (G-P) zones provides the information on the corrosion resistance of these a...
Corrosion Science, 2007
The corrosion behaviour of Al-5Zn-3Mg-0.6Cu-0.8Zr-0.25Cr-0.15Ni-0.15Ti alloys, produced by traditional and powder technologies, with similar thermo-mechanical treatments, in 3% sodium chloride solution, has been examined by electrochemical methods, scanning electron microscopy, transmission electron microscopy and X-ray microanalysis. The alloys reveal similar precipitation but of different shape, size and distribution; further, both alloys experience localized corrosion. Copper-rich precipitates initiate the dissolution of surrounding particles, enriched in Zn and Mg. As a result, the surface is enriched with other alloying elements after a full polarisation run. Cast material has lower corrosion properties because of the higher heterogeneity of the structure. The structure heterogeneity of the cast material involves a more non-uniform distribution of the precipitates, larger Zn-and Mg-rich particles, and depletion of the matrix and areas around the precipitates by alloying elements compared with the powder material.
Effect of Grain Refinement on Electrochemical Behavior of Al– Zn–Mg–Cu Alloys
International Journal of Electrochemical Science, 2016
The influence of Yb, Cr and Zr additives on electrochemical corrosion and stress cracking corrosion behavior of Al-6.2Zn-2.3Mg-2.3Cu (mass fraction) alloys was investigated using open circuit potential, electrochemical impedance spectroscopy, cyclic polarization and U-type method. Better corrosion resistance of Al alloys was obtained through grain refinement effect by adding 0.16Zr and 0.16Zr-0.18Cr-0.3Yb. Both strength and corrosion resistance are inversely proportional to grain size, showing a Hall-Petch relation. The mechanism of grain refinement effect was revealed by TEM.
Influence of chemical composition on corrosion resistanceof AZ91D magnesium alloy ingots
Paper presents the results on the corrosion behavior of some Al-Fe-Si, Al-Mg-Si and Al-Mg-Mn alloys in their final commercially usable tempered state. Durability of alloys was quantified and compared in the sense of corrosion rates in aqueous solutions while also having in mind the role of alloy chemistry. Open circuit corrosion potential (OCP) measurements, linear polarization and potentiodynamic anodic/cathodic polarization was employed in order to determine the corrosion behavior of samples in the mixture of chloride ions containing aqueous corrosion ambient. We found out that AlFe0.83Si0.18(AA8079), AlMg0.63Si0.72 (AA6005) and AlMg4Mn (AA5182) alloy exhibited the highest rates of passivation in 0.51 mol NaCl solution. The group of Al-Fe-Si alloys exhibited the greatest sensitivity to the changes in chemical composition under potentiodynamic polarization. Artificially aged Al-Mg-Si extruded profiles and fully annealed (after cold rolling) Al-Mg-Mn sheets exhibit very similar levels of equilibrium potentials E (I=0) in 0.51 mol NaCl solution. In the case of Al-Fe-Si alloys, we found that Fe/Si ratio also plays an important role, next to the total content of Fe and Si. Alloys with high Fe/Si ratios showed almost 30 % lower polarization resistance compared to the alloys with balanced Fe/Si, even in the case of the equal total content of alloying elements. The AlMg0.7Si1.2Mn0.8 alloy aged after quenching in the sprayed water and AlMg4Zn1.3Mn0.4 annealed sheet exhibit very similar levels of corrosion rates in 0.51 mol NaCl solution.
International Journal of Chemical Engineering
Cathodic electrodeposition (CED) was used to coat the cast magnesium alloy Mg-9Al-1Zn-xRE with aluminum powder and epoxy. Immersion and salt spray tests (ASTM B117) at room temperature for a total of 240 hours have been performed to assess the corrosion performances of AZ91D magnesium alloy. At each 24-hour interval, the samples were checked for any damage or deterioration of the coating surface morphology. The X-ray diffraction (XRD) analysis confirmed the phases, and scanning electron microscopy (SEM) with EDS analysis confirmed the phase composition. The electrochemical results show that CED epoxy coatings have superior adhesiveness and corrosion resistance compared to powder-coated aluminum and cast magnesium. The salt spray and immersion test results also confirm that CED epoxy coating exhibits good corrosion resistance.