The diffusion and trapping of H in overaged commercial 7xxx series alloys of the second and third generation is first studied using an enhanced electrochemical permeation method involving sputter etching of the native oxide and hydrogen charging by alkaline corrosion at the open circuit potential. Proof of concept is provided demonstrating remarkable experimental reproducibility and addressing common experimental errors, such as native oxide films, localized corrosion and buildup of corrosion products. A commercial second and third generation 7xxx series alloy exhibit effective H diffusion coefficients of 1.6 +/- 0.7 x 10-10 cm2/s and 3.7 +/- 0.3 x 10-10 cm2/s, respectively. The different H diffusivities were explained by extensive H trapping in coarse intermetallic Al7Cu2Fe and S-phase particles, alongside potential trapping at the interface of quenchinduced grain-boundary precipitates with lower Zn content.

The formation of surface films and local alkalization during the aqueous corrosion of Mg alloys significantly influence their corrosion properties across various electrolytes. This study provides new insights into the layer formation on a Mg-1.06Al-0.046Ca alloy immersed in an alkaline electrolyte (pH = 11.5) for 72 h utilizing (electro-)chemical and microstructural analysis. Scanning transmission electron microscopy and atom probe tomography reveal a subsurface Al-enriched interlayer (similar to 4 at%) and the absence of Ca segregation at the metal and corrosion product interface. The corrosion product itself is a three-layer structure: next to the substrate a Mg(OH)2_dense layer, followed by an Al-enriched interlayer 2, and an outer Mg(OH)2_flake layer. Changes in diffusion-related transport properties are observed after 20.5 h of immersion, as indicated by the impedance response associated with the Mg(OH)2_dense layer and the subsurface Al interlayer 1. A similar to 1.5 mu m deformation layer persists after 72.0 h immersion in a pH of 11.5 and dominates the corrosion behavior.Subsurface Al enrichment (similar to 4 at%) occurs within the metallic substrate.Two distinct corrosion stages are identified with a transition from Ca- to Al-dominated dissolution.Capacitive layer properties appear diffusion-controlled according to Fick's law.

Aluminum (Al) alloys are the most commonly used materials for stochastic open-cell metal foams. However, alternative nickel (Ni)-based systems, such as stochastic open-cell Ni/polyurethane and Ni/Al foams, have achieved considerable technological advancement in recent years. The present study provides a direct comparison of these material systems with respect to their initial mechanical properties, their electrochemical corrosion behavior in a stagnant 3.5 wt.% NaCl electrolyte and the resulting impact on the mechanical performance after six months of immersion. The results reveal a lower initial mechanical strength and energy absorption capacity for the Al foam system. Moreover, the stochastic open-cell Al foams exhibit microgalvanically induced dissolution, leading to a linear degradation of the mechanical properties under uniaxial compression. In contrast, the Ni-based systems show a significantly reduced effect of electrochemical corrosion on their mechanical behavior. Overall, the findings demonstrate a distinct advantage of the Ni-based material systems for energy absorption applications under realistic service conditions compared to stochastic open-cell Al foams.

The native oxide formed on polished surfaces of two commercial Al-Zn-Mg-Cu alloys of the 7xxx series with high (7.3 wt%) and moderate (6.2 wt%) Zn content was studied to elucidate the surface chemistry and potential influences on corrosion initiation. XPS, ToF-SIMS and XRR were used to analyze surface chemistry, oxidation states of major alloying elements and oxide thickness. Both matrix and Cu containing coarse intermetallic particles were considered. The thicknesses of the hydroxylated matrix oxides were 5.2 +/- 0.6 nm. A metallic Cu enrichment of similar to 10 at.% was found at the oxide/metal interface for Cu contents of 1.7 and 2.1 wt%, while no Cu incorporation into the matrix oxide layer was observed. Surface concentrations of Zn and Mg were correlated with the bulk alloy composition. Besides minor Mg enrichment in the oxide, we report an unprecedented amount of Zn near the oxide/metal interface that exceeds the bulk concentration by a factor of similar to 2. Significant Zn oxidation was found within the oxide layer, where the metallic/oxidized Zn ratio increases for higher bulk Zn concentrations, potentially altering the surface reactivity during corrosion. Additionally, the oxide on a Cu containing coarse intermetallic particle is thinner than on the matrix with similar segregation mechanisms.

This study explored the impact of minor Cr and Ag additions on the resistance of a new generation Al-8Zn-2Mg-2Cu-0.1Zr alloy to hydrogen environmentally assisted cracking (HEAC) in humid air. The results show that HEAC in Al-8Zn-2Mg-2Cu-0.1Zr alloy can be suppressed by 0.1 wt% Cr addition, due to the formation of E-Al18Mg3Cr2 dispersoids with a high H binding energy and possibly a less electrochemically active grain boundary (GB) microchemistry. similar to 0.3 wt% Ag addition in Al-8Zn-2Mg-2Cu-0.1Zr alloy had no influence on the HEAC susceptibility, despite 1 at% Ag partitioning in the GB eta-Mg(Zn,Cu,Al)(2) and a minor decrease in the PFZ width.

The effect of varying Al concentrations on the electrochemical corrosion resistance of binary Mg-Al solid solutions thin films under alkaline immersion conditions was investigated via a combination of in-situ flow-cell, scanning vibrating electrode technique and microscopy analysis. These spatially resolving characterization techniques are employed along the Al concentration gradient of the combinatorically grown thin films enabling efficient screening of the Al concentration dependent electrochemical corrosion behaviour. The analysis revealed an increasing corrosion resistance with increasing Al concentration, as a consequence of Al induced hydroxide reinforcement. Specifically, the addition of >4 wt.% Al decreases the corrosion current density in the range of 70–90 % compared to pure Mg.

The structure and composition of the native oxide forming on the basal plane (0001) of the magnesium-based alloy Mg-2Al-0.1Ca was investigated by combining scanning transmission electron microscopy (STEM) and atom probe tomography (APT). While STEM measurements demonstrated the growth of a (111) MgO oxide layer with 3-4 nm thickness on the basal (0001) plane of the atom probe specimen, APT data further revealed the formation of an aluminum-rich region between bulk magnesium and the native oxide. The aluminum enrichment of up to ~20 at.% at the interface is consistent with an inward growth of the oxide scale.

The electrochemical corrosion mechanisms of Mg alloys were extensively studied in previous investigations of different chemical compositions, modified surface states and various electrolyte conditions. However, recent research focused on the active state of Mg dissolution, leading to unresolved effects of secondary phases adjacent to a stable α-solid solution passive layer. The present study investigates the fundamental electrochemical corrosion mechanisms of three different Laves phases with varying phase morphologies and phase fractions in the passive state of Mg-Al-Ca alloys. The microstructure was characterized by (transmission-) electron microscopy and synchrotron-based transmission X-ray microscopy. The electrochemical corrosion resistance was determined with a standard three-electrode setup and advanced in-situ flow cell measurements. A new electrochemical activity sequence (C15>C36>α-Mg>C14) was obtained, as a result of a stable passive layer formation on the α-solid solution. Furthermore, nm-scale Mg-rich precipitates were identified within the Laves phases, which tend to inhibit the corrosion kinetics.

Mg-based alloys are industrially used for structural applications, both as solid solutions alloys and as composites containing intermetallic compounds. However, a further development in terms of mechanical properties requires the investigation of underlying causalities between synthesis, processing and microstructure to adjust the mechanical and the corrosion properties, ideally down to the near atomic scale. Such fundamental scientific investigations with high resolution characterisation techniques require model materials of exceptionally high purity and strictly controlled microstructure e.g. with respect to grain size, morphology, chemical homogeneity as well as content and size of oxide inclusions. In this context, the Mg-Al-Ca system appears exceptionally challenging from a metallurgical perspective due to the high reactivity and high vapor pressures, so that conventional industrial techniques cannot be successfully deployed. Here, we demonstrate the applicability of various scientific synthesis methods from arc melting over solution growth to diffusion couples, extending to effects and parameters for thermo-mechanical processing. Suitable pathways to overcome the specific challenges of the Mg-Al-Ca system are demonstrated, as well as the persistent limitations of the current state of the art laboratory metallurgy technology.

White etching areas (WEA) and white etching cracks (WEC) are frequently linked to premature bearing failure in conventional high carbon bearing steels like 100Cr6 (SAE 52100). In contrast, no WEA/WEC has yet been reported for the high nitrogen bearing steel X30CrMoN15-1 (SAE AMS 5898). Thus, the present study proves for the first time that X30CrMoN15-1 is also susceptible to develop WEA/WEC under rolling contact fatigue (RCF) when pre-charged with hydrogen. RCF tests conducted in parallel without hydrogen pre-charging resulted in RCF damage only, which identifies hydrogen as an active agent for WEA/WEC formation in X30CrMoN15-1. These findings correspond to the fact that hydrogen diffusion during RCF is often considered to cause or accelerate the formation of WEA/WEC. Additionally, it is observed that the M2(C, N) and M23C6 precipitates of the martensitic microstructure of the X30CrMoN15-1 do not entirely decompose during the WEA formation process as observed for M3C precipitates in 100Cr6. In conclusion, the results for X30CrMoN15-1 strongly suggest that the formation of WEA is driven by a hydrogen-activated local severe plastic deformation process, which initiates continuous dynamic recrystallisation, leading to the characteristic nano-ferritic grains observed in WEA. Also, the highly stable and self-regenerating passive chromium-oxide layer of X30CrMoN15-1 mitigates the risk of WEA/WEC failure during typical RCF operation by hindering the formation and adsorption of ionic hydrogen. Hence, this study emphasises the importance of protecting the base material against hydrogen ingress to delay WEA/WEC formation.

In this study, the influence of minor Ag addition on the microstructure, mechanical and corrosion properties of an Al-Zn-Mg-Cu-Zr (7449) alloy with Zn/Mg ratio of 4 was systematically investigated using various materials characterization techniques, Slow Strain Rate Test (SSRT), Potentiodynamic Polarization (PDP) and Intergranular Corrosion (IGC) measurements. Microstructure characterization by Scanning Electron Microscopy (SEM) and Differential Scanning Calorimetry (DSC) showed that Ag partitioning in the eutectic Mg(Zn,Cu,Al)(2) phase occurs resulting in an increase in its solvus line. After processing to the T4 condition, Ag was partially in solid solution with the excess forming an Ag-rich AlAgZnMgCu phase. Scanning-Transmission Electron Microscopy (STEM) showed evidence of quench-induced eta-Mg(Zn,Cu,Al)(2) precipitates at the grain boundaries (GBs) in the T4 condition with similar to 3 at.% Ag in the Ag-modified alloy. STEM and Atom Probe Tomography (APT) confirmed that similar to 1 at. % Ag was present in both the matrix and GB precipitates in the Ag-modified alloy after T76 aging. Furthermore, the frequently reported decrease in the PFZ width with Ag addition was not observed after T76 aging, with both alloys having a similar PFZ width. Despite higher hardness/strength in the T4 condition with Ag addition, no enhanced age hardening response and alteration of the precipitation kinetics was observed during artificial aging at 121 degrees C. In fact, Ag addition in a 7xxx alloy with Zn/Mg ratio of 4 was found to be detrimental to mechanical properties, stress corrosion cracking, pitting and IGC resistance after T76 aging, which is attributed to the presence of the Ag-rich AlAgZnMgCu phase.

Microstructure optimization of Al-Zn-Mg-Cu-Zr aluminum alloys, particularly through recrystallization inhibition, for improved strength and corrosion resistance properties has been an important consideration in alloy development for aerospace applications. Addition of rare earth elements, sometimes combined with Cr, has been found to be beneficial in this regard. In this study, the role of a single addition of 0.1 wt.% Cr on microstructure evolution of an Al-Zn-Mg-Cu-Zr (7449) alloy during processing was systematically investigated by optical light microscopy, scanning electron microscopy, electron backscatter diffraction and scanning transmission electron microscopy. Susceptibility to localized corrosion after aging to T4, T6 and T76 conditions was evaluated by potentiodynamic polarization (PDP) measurements and an intergranular corrosion (IGC) test. A decrease in recrystallized fraction with 0.1 wt.% Cr addition was observed, which is attributed to the formation of Cu- and Zn-containing E (Al18Mg3Cr2) dispersoids and the larger as-cast grain size. Moreover, the depletion of alloying elements from solid solution due to the formation of the Cu- and Zn-containing E (Al18Mg3Cr2) dispersoids and η Mg(Zn,Cu,Al)2 phase at its interface affects grain-boundary precipitation. The observed decrease in localized corrosion susceptibility with minor Cr addition is correlated with the microstructure and equally discussed.

The role of the (Fe,Al)(2)Nb Laves phase on the high temperature oxidation mechanisms of Fe-26Al-4Nb (at%) was investigated between 700 degrees C and 1000 degrees C in air for 500 h. The (Fe,Al)(2)Nb Laves phase that was already present in as-cast state was selectively oxidised at all temperatures but showed the formation of different oxides including Fe2O3, AlNbO4, and Al-rich oxide depending on test temperature. Unharmed (Fe,Al)(2)Nb was newly formed below the oxide scale at 700 degrees C and 800 degrees C, while at 900 degrees C and 1000 degrees C no unharmed Laves phase below the oxide layer was observed. The discontinuous isothermal testing showed a change of kinetics at 700 degrees C and 800 degrees C after 10 h of oxidation. At 1000 degrees C, the (Fe,Al)(2)Nb Laves phase was additionally identified to initiate oxide spallation.

Mg-Al-Ca alloys with Laves phase reinforcement are suitable for structural applications. The composition, crystal structure, and distribution of Laves phases can be tuned by the alloy composition and heat treatment, which subsequently influence their mechanical properties. In this study, three model alloys Mg-6Al-2Ca, Mg-5Al-3Ca and Mg-4Al-4Ca were investigated, which include C15, C36, and C14 Laves phases. The as-cast alloys have interconnected Laves phases that form a skeleton structure. After annealing, they became more rounded particles, while the metastable C36 phase was transformed to C15. The Laves phases in different crystal structures exhibit distinct ranges of chemical compositions and lattice parameters. Well defined orientation relationships were observed between small C15 platelets and the Mg matrix (Mg(0002) // C15(111), Mg[112̅0] // C15[112̅]). Another pair of parallel orientations was found between Mg(11̅01) and the c-plane of hexagonal C36/C14. Nevertheless, most coarsened Laves phases have incoherent interfaces with the matrix and hinder dislocation slip transfer. The annealed alloys have lower yield strength than their as-cast counterparts, but higher ductility or ultimate tensile strength. The yield strengths of as-cast alloys are correlated to the interconnectivity of the skeleton, whereas those of annealed alloys are related to the spacing between Laves phases.

With an ongoing discussion on the oxygen diffusion along crystal defects remaining, it is difficult to study this phenomenon in Al containing intermetallic materials due to its rapid and passivating oxide formation. We report here the observation of enhanced oxygen diffusion along crystal defects, i.e. dislocations and twin boundaries, in the C15 Al 2 Ca Laves phase and how the presence of oxygen induces structural changes at these defects. Three main phases were identified and characterized structurally by aberration-corrected, atomic resolution scanning transmission electron microscopy, analytically by energy dispersive X-ray spectroscopy and electron energy loss spectroscopy. Unlike the C15 bulk phase, the twin boundary and dislocation transformed into a few nanometer wide amorphous phase, which depletes in Al and Ca but is highly enriched in oxygen. The dislocation even shows coexistence of the amorphous phase with a simple Al-rich A1 fcc phase. This A1 phase only depletes in Ca, not in Al (Al remains at bulk concentration), and is also enriched in oxygen. The Al-rich A1 phase is coherent with the C15 matrix. Electron energy loss spectroscopy revealed the amorphous phase to be Al 2 O 3 . We thereby show as one of the first studies that oxygen diffusion along crystal defects, especially also at the twin boundary can induce the formation of an amorphous oxide along themselves. The identification of oxygen-induced transformation at strained defects has to be considered when the material is exposed to air during plastic deformation at elevated temperatures.

The time dependent native oxide surface conditions of Mg and Mg-Al-Ca alloys under moderate atmospheric conditions were continuously analysed via in situ SKPFM, in situ XRR and ex situ XPS measurements. The progressive hydration of the MgO layer appears to be the dominant surface reaction for all investigated alloys during the investigated time period up to 24 h. Subsequent electrochemical measurements revealed a reduced corrosion resistance of all Mg alloys under short-term immersion conditions with a higher hydration degree of the native oxide.

In this paper, the high strength and lightweight Al–Cu–Li alloy (AA2099) is considered in as-built and preheated conditions (440 °C, 460 °C, 480 °C, 500 °C, and 520 °C). The purpose of this study is to investigate the influence of laser powder bed fusion (LPBF) in situ preheating on precipitation microstructure, mechanical and corrosive properties of LPBF-printed AA2099 alloy compared to the conventionally processed and heat-treated (T83) alloy. It is shown that precipitations evolve with increasing preheating temperatures from predominantly globular Cu-rich phases at lower temperatures (as-built, 440 °C) to more plate and rod-like precipitates (460 °C, 480 °C, 500 °C and 520 °C). Attendant increase with increasing preheating temperatures are the amount of low melting Cu-rich phases and precipitation-free zones (PFZ). Hardness of preheated LPBF samples peaks at 480 °C (93.6 HV0.1), and declines afterwards, although inferior to the T83 alloy (168.6 HV0.1). Preheated sample (500 °C) shows superior elongation (14.1%) compared to the T83 (11.3%) but falls short in tensile and yield strength properties. Potentiodynamic polarization results also show that increasing preheating temperature increases the corrosion current density (Icorr) and corrosion rate. Indicated by the lower oxide resistance (Rox), the Cu-rich phases compromise the integrity of the oxide layer.

The electrochemical corrosion rate of Magnesium (Mg) and Mg alloys depends on the stability of the formed surface layer. Based on the Mg substrate, the oxide structure comprises a dense MgO/Mg(OH)2 mixture underneath a porous plate-like Mg(OH)2 layer. While the kinetics of the anodic partial reaction has been mainly attributed to MgO, recent studies showed an effect of the Mg(OH)2 layer thickness on the cathodic partial reaction. A thinner Mg(OH)2 layer has been associated with a higher kinetics of the oxygen reduction rate. In the present study, the proposed mechanism has been further investigated via in situ respirometric measurements with Mg-Al-Ca solid solution in electrolytes with different pH values (pH = 8-13). The results indicate an additional effect based on the structure of the surface layer in the passive state of Mg corrosion. Furthermore, two different Al enriched interlayers at the Mg/MgO- and MgO/Mg(OH)2 interfaces were observed and discussed in terms of their thermodynamic stability under alkaline immersion conditions.

The mechanical properties of a Fe-19Al (at.%) alloy containing 5 at.% Cr as the main alloying element are presented and discussed. While the alloy behaves brittle at room temperature and 100 & DEG;C, tensile stress-strain curves at temperatures between 200 & DEG;C and 500 & DEG;C show strain hardening recovery effects similarly to those of fcc twinning induced plasticity (TWIP) steels. It is supposed that a combination of dislocation glide and formation of internal boundaries in the submicron range leads to similar strain hardening stages at intermediate temperatures (200 & DEG;C-500 & DEG;C) in the FeAl alloy as usually observed in TWIP steels at room temperature. The maximum strain hardening rate after recovery reaches very high values of about G/19 at 400 & DEG;C. Low-cycle fatigue (LCF) tests at 400 & DEG;C and 500 & DEG;C up to strain amplitude values of 0.6% and stress-relaxation tests do not reveal high back stresses or pseudoelasticity in the FeAl alloy. This indicates that the deformation structures responsible for the strain hardening rate recovery remain stable upon stress relief.

Although anionic surfactants have been widely introduced as inhibitors against uniform corrosion, their efficiency as pitting inhibitors remains unclear. Herein, fatty alcohol ether sulfate (FAES), linear alkylbenzene sulfonate (LAS), and palm kernel oil (PKO) were tested for a Ti‐stabilized (1.4510) and a nonstabilized grade (1.4016) of ferritic stainless steel in alkaline chloride solutions containing H 2 O 2 . Electrochemical impedance spectroscopy (EIS) measurements were performed to elucidate the adsorption of surfactants at OCP, followed by potentiodynamic polarization. For 1.4510, LAS and FAES did not significantly affect the EIS results but inhibited pitting initiation with identical efficiencies. In the case of 1.4016, Cr‐rich carbides acted as adsorption sites, where LAS showed higher efficiency than FAES. While LAS and FAES interact preferentially with pitting initiation sites, PKO appears to adsorb randomly on the passive film. Consequently, inhibition can reach a maximum due to the electrical neutralization of the surface. Finally, LAS can be effective as an inhibitor for stainless steel containing carbides that can lead to pitting initiation.