Exfoliation corrosion of Al–Zn–Mg–Cu–Zr alloy containing Sc examined by electrochemical impedance spectroscopy

The exfoliation corrosion behavior of an Al–Zn–Mg–Cu–Zr alloy containing Sc artificially aged at 120 °C for 24 h is studied by macroscopic observation techniques and electrochemical impedance spectroscopy (EIS) measurements. After 48 h immersion, the blisters start bursting and delamination initiates, along with the appearance of two time constants in the impedance diagrams. According to the simulation by equivalent circuit, the corrosion rate decreases sharply and then reaches a steady state, which is due to the change of the solution pH and oxide layer thickness, as well as the accumulation of corrosion products.     

Mechanical properties,corrosion behavior,and microstructure of Sr modified Al–9.2Mg–0.7Mn alloys

The influence of strontium (Sr) additions in the form of Mg–Sr master alloys from 0 to 0.6 wt% on the mechanical properties, corrosive nature, and microstructure of Al–9.2Mg–0.7Mn alloys is investigated. The material is studied in a fully annealed (O‐temper) and a sensitizing treatment at 150°C for 7 days. Here we demonstrate that there will be a new phase which might be (Al, Mg)₁₇Sr₂ formed in the as‐cast microstructure. When the Sr content is 0.2 wt%, under the premise that the mechanical properties of completely annealed alloy change little (relative to the matrix: the ultimate tensile strength increases by 8 MPa and the elongation only decrease by 1.6%), the intergranular corrosion resistance is significantly improved. The specific performance is that the mass loss from intergranular corrosion decreases by more than 53% from the addition of 0.2 wt% Sr after sensitizing.     

SKPFM investigations of intermetallic compounds of innovative Er‐ and Zr‐containing Al–Si–Mg alloys and their influence on corrosion localization in saline solution

The paper aims at characterizing the influence of intermetallic compounds on the corrosion localization of innovative Al–Si–Mg Er‐ and Zr‐containing casting alloys. Samples of the investigated materials were studied by means of optical and scanning electron microscope micrographs, immersion tests, and scanning Kelvin probe force microscope (SKPFM) analyses in the T6 temper. Combination of immersion tests and SKPFM analyses allowed to identify those classes of intermetallic compounds promoting localization of the corrosion process. It was found that intermetallic compounds richer in Fe were the most critical for corrosion localization; furthermore, additions of Er caused a marked decrease of the potential difference of intermetallic compounds with respect to the Al matrix and a consequent less intense microgalvanic coupling, which translates into slower corrosion kinetics. Further, Zr additions slightly increased the potential difference of intermetallic compounds with the Al matrix, promoting a faster corrosion process.     

Analysis of the texture of heterogeneous Al–Cu–Fe coatings containing quasicrystalline phase

The structure of heterogeneous Al–Cu–Fe coatings produced by electron beam physical vapour deposition was studied. The coating compositions were varied close to the optimal composition of icosahedral phase. Axial textures of both icosahedral and β-cubic phase were observed. The type of axial texture of quasicrystalline component correlates with the texture type of the crystalline phase.     

Research on intercrystalline corrosion,exfoliation corrosion,and stress corrosion cracking of Al–Zn–Mg–Sc–Zr alloy

The intercrystalline corrosion, exfoliation corrosion (EXCO), and stress corrosion cracking (SCC) of Al–Zn–Mg–Sc–Zr alloy were investigated by means of constant temperature immersion corrosion method, optical microscopy, transmission electron microscopy (TEM), and electrochemical impedance spectroscopy (EIS). The results show that intercrystalline corrosion, and EXCO susceptibility of Al–Zn–Mg–Sc–Zr alloy decrease gradually with increasing of aging time. Corrosion susceptibility order from low to high is as follows: OA > PA > UA > NA. The SCC susceptibility index of PA temper is more than OA temper at the same strain rate. According to TEM observation, with aging time prolonging, a part of η′ phases transform to η equilibrium phases, which become coarse gradually. The distribution discontinuity of the grain boundary precipitates increases. In addition, for Al–Zn–Mg–Sc–Zr alloy without EXCO, the EIS is comprised by a capacitive impedance arc at high frequency and an inductive impedance arc at low frequency. Once EXCO occurs, the EIS is composed of two capacitive impedance arcs at high frequency and at low frequency, respectively.     

Correlation of stress corrosion cracking behaviour with electrical conductivity and open circuit potential in Al‐Li‐Cu‐Mg‐Zr alloys

Studies of stress corrosion cracking (SCC) behaviour by slow strain rate test (SSRT), potentiodynamic electrochemical polarization and measurement of electrical resistivity were carried out on 8090 and 1441 Al‐Li‐Cu‐Mg‐Zr alloys in their peak aged T8, over aged T7 and retrogressed and reaged (RRA) T77 tempers. It has been found that the SCC resistance is maximum in the T7 temper, least in the T8 temper and in the RRA T77 tempers it lies in between to that of the T8 and T7 tempers, indicating that RRA heat treatment given to the T8 temper of both alloys caused an improvement of SCC resistance. Further, studies on the electrical conductivity measurements and electrochemical polarization of all tempers of both alloys showed that T7 temper has maximum electrical conductivity and most negative (anodic) open circuit potential (OCP), T8 has the minimum and the least respectively, whereas, in the T77 tempers these values lie in between to those of the T8 and T7 tempers. Therefore, a definite pattern of variation of these results with RRA treatment draws an attention to correlate SCC behaviour, electrical conductivity and OCP values which are explained on the basis of microstructural features revealed by TEM and XRD studies.     

The electrochemical behavior of Mg–9Al–0.5Zn,Mg–9Al–0.7Zn,and Mg–9Al–1.0Zn in a NaCl solution

In this study, the electrochemical behavior of Mg–9Al–0.5Zn, Mg–9Al–0.7Zn, and Mg–9Al–1.0Zn electrodes in a 0.7 mol L^?1 NaCl solution is evaluated by using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and potentiostatic oxidation. The utilization efficiencies of these materials are also determined. The results show that the Mg–9Al–1.0Zn alloy has the highest corrosion resistance and that Mg–9Al–0.5Zn displays the largest discharge current in the 0.7 mol L ^?1 NaCl solution at 25°C. In addition, the utilization efficiencies of the alloys decrease as follows: Mg–9Al–1.0Zn > Mg–9Al–0.7Zn > Mg–9Al–0.5Zn. This study illustrates that doping Zn into Mg‐Al electrodes increases the corrosion resistance and utilization efficiency but decreases the discharge activity of Mg–Al–Zn anodes when the Zn content is between 0.5% and 1.0%.     

A contribution to the Al–Pd–Mn phase diagram

A part of the Al–Pd–Mn phase diagram in the vicinity of the icosahedral phase was refined. Partial isothermal sections of 710, 850, 870 and 880°C are presented. The overall compositional range of the icosahedral phase was found to be between 5.8 and 10.5 at.% Mn and between 69.5 and 71.5 at.% Al at these temperatures. It shifts to lower Mn concentration at lower temperatures. It was confirmed that the phase usually designated Al₃Pd has a lower Al concentration in the binary alloys than that according to the formula. It extends to the ternary compositions up to about 5 at.% Mn. The increase of the Mn content results in an increase of the Al concentration of this phase.     

The microstructures and mechanical properties of cast Mg–Zn–Al–RE alloys

The microstructures and mechanical properties of cast Mg–Zn–Al–RE alloys with 4 wt.% RE and variable Zn and Al contents were investigated. The results show that the alloys mainly consist of α-Mg, Al₂REZn₂, Al₄RE and τ-Mg₃₂(Al,Zn)₄₉ phases, and a little amount of the β-Mg₁₇Al₁₂ phase will also be formed with certain Zn and Al contents. When increasing the Zn or Al content, the distribution of the Al₂REZn₂ and Al₄RE phases will be changed from cluster to dispersed, and the content of τ-Mg₃₂(Al,Zn)₄₉ phase increased gradually. The distribution of the Al₂REZn₂ and Al₄RE phases, and the content of β- or τ-phase are critical to the mechanical properties of Mg–Zn–Al–RE alloys. The Mg–6Zn–5Al–4RE alloy with cluster Al₂REZn₂ phase and low content of β-phase, exhibits the optimal mechanical properties, and the ultimate tensile strength, yield strength and elongation are 242 MPa, 140 MPa and 6.4% at room temperature, respectively.     

Corrosion behaviour of Mg–Al alloys with Al–11Si thermal spray coatings

The corrosion resistance of AZ31, AZ80 and AZ91D Mg–Al alloys with Al–11Si thermal spray coatings was evaluated by electrochemical and gravimetric measurements in 3.5 wt% NaCl solution. The changes in the morphology and corrosion behaviour of the Al–11Si coatings induced by a cold‐pressing post‐treatment under 32 MPa were also examined. The as‐sprayed Al–11Si coatings revealed high degree of porosity and poor corrosion protection, which resulted in galvanic acceleration of the corrosion of the magnesium substrates. The application of a cold‐pressing post‐treatment produced more compact Al–11Si coatings with better bonding at the substrate/coating interface and slightly higher corrosion resistance. However, interconnected pores remained in the cold‐pressed coatings due to the low plasticity of the Al–11Si powder and galvanic corrosion of the substrate was observed after immersion in 3.5 wt% NaCl for 10 days.     

Thermodynamic analysis of alloys Ti–Al, Ti–V, Al–V and Ti–Al–V

Thermodynamic analysis of three binary Ti-based alloys: Ti–Al, Ti–V, and Al–V, as well as ternary alloy Ti–Al–V, is shown in this paper. Thermodynamic analysis involved thermodynamic determination of activities, coefficient of activities, partial and integral values for enthalpies and Gibbs energies of mixing and excess energies at four different temperatures: 2000, 2073, 2200 and 2273 K, as well as calculated phase diagrams for the investigated binary and ternary systems. The FactSage is used for all thermodynamic calculations.