Search

In the present study, the distribution of Ag in the coating formed on Mg-Ag alloy by plasma electrolytic oxidation (PEO) and its ionic release kinetics when exposed to a 0.9 wt.% NaCl solution at 37 °C have been investigated. Both metallic Ag and Ag oxide particles with ∼5 to ∼40 nm in diameters were observed in the PEO coating. Further, an Ag-enriched layer of ∼20 nm in thickness at the substrate/coating interface was also observed. The PEO coating on the Mg-Ag alloy not only increases its corrosion resistance with the corrosion current density decreasing by up to 3 orders of magnitude from 8.04 × 10−3 to 4.03 × 10−6 A/cm2, but also controls the release of Ag+ to the level that is sufficient for anti-infective efficacy without causing cytotoxicity to mammal cells. [ABSTRACT FROM AUTHOR]

Al-5Ti-1B is the most widely used grain refiner for Al alloys. However, it is not effective for grain refining Al alloys containing more than 3 wt pct Si. This adverse effect of Si is referred to as Si poisoning. In spite of extensive experimental and theoretical investigations in the past decades, the exact mechanism for Si poisoning is still not clear. In this work, the state-of-the-art electron microscopy was performed to investigate the mechanism for Si poisoning. Our experimental results suggest that Si segregates preferably to the TiB2/Al-Si melt interface and the pre-existing Al3Ti 2-dimensional compound (2DC) layer on TiB2 surface dissolves into the Al-Si melt. Based on the experimental results, we have postulated a new mechanism for Si poisoning: interfacial segregation of Si leads to enrichment of Si at the TiB2/Al-Si melt interface, and this in turn makes the pre-existing Al3Ti 2DC on the TiB2 surface unstable and dissolve gradually in the melt, resulting in a loss of TiB2 nucleation potency and hence a decreased total number of potent TiB2 particles available for heterogeneous nucleation and grain initiation and consequently an increased grain size. This mechanism for Si poisoning can explain consistently the experimentally observed phenomenon reported in the literature. [ABSTRACT FROM AUTHOR]

In the present study, the influence of precipitate distribution on the corrosion behaviour of 2A97-T6 Al-Cu-Li alloy in 3.5 wt.% NaCl solution is investigated. It is found that localized plastic strain introduced to the alloy during sheet fabrication leads to the formation of dense T 1 (Al 2 CuLi) phase precipitate bands and precipitate-free bands within selected grains during aging. Preferential dissolution of T 1 phase in the dense precipitate bands results in intragranular corrosion in the alloy, in the form of corrosion bands. Further, the dissolution of the alloy matrix propagates in the form of crystallographic corrosion pit. [ABSTRACT FROM AUTHOR]

In the present work, the influence of trace level Cu on intergranular corrosion (IGC) in AA6082 Al–Mg–Si alloy is studied using correlative accelerated corrosion testing and high resolution electron microscopy. Further, grain boundary structure and its correlation to IGC are also investigated using electron backscatter diffraction (EBSD) and transmission Kikuchi diffraction (TKD). It is found that in AA6082-T6 alloy with very low Cu content (0.06 wt%), about 13% of high angle grain boundaries have Al 2 Cu precipitates, which promotes IGC at the grain boundaries. • In AA6082-T6 alloy with 0.06 wt % Cu, Al 2 Cu precipitates are present at 13% of high angle grain boundaries. • Low angle grain boundaries in the AA6082-T6 alloy are almost free of precipitates. • The presence of Al 2 Cu precipitates at high angle grain boundaries increases susceptibility to IGC in acidified NaCl solution. • Low angle grain boundaries show low susceptibility to intergranular corrosion in acidified NaCl solution. [ABSTRACT FROM AUTHOR]

• Compared to that with lower stored energy, grain with higher stored energy is more susceptible to corrosion. • Copper tends to segregate at dislocations. • Grain with higher stored energy displays a more negative surface potential compared to that with lower stored energy. • Using stored energy distribution, intergranular corrosion could be predicted. In the present work, microstructure and intergranular corrosion behaviour of AA2024-T3 alloy are studied. Using electron diffraction techniques to correlate stored energy distribution with corrosion propagation path, intergranular corrosion tends to occur in the periphery of grain with relatively high stored energy. Further, it is revealed that Cu tends to segregate at dislocations, resulting in high Cu content of grain with high stored energy, which promotes corrosion propagation into its interior. In addition, based on the relationship between stored energy and boundary attack, intergranular corrosion during the immersion in NaCl solution could be successfully predicted. [ABSTRACT FROM AUTHOR]

• Corrosion occurs preferentially in non-recrystallized regions. • Subgrain boundaries decorated with T 1 precipitates are preferred sites for corrosion initiation. • Local corrosion susceptibility is strongly correlated to grain stored energy. • Cu-enriched layer is developed at the crevice wall of attacked grain boundaries. In the present study, correlative corrosion testing and electron microscopy, including quasi-in-situ electron microscopy, are employed to investigate the corrosion behaviour of 2A97-T8 Al-Cu-Li alloy extrusion in 3.5 wt% NaCl solution. It is found that the corrosion behaviour of the alloy is influenced by synergetic effect of the plastic deformation introduced by the thermomechanical processing during alloy fabrication and the precipitation of T 1 phase during T8 treatment. Localized corrosion initiates and propagates preferentially within non-recrystallized regions of the partially recrystallized alloy. Corrosion initiated at coarse constituent intermetallic particles is confined to its periphery, which doesn't develop further when the particles are disconnected from alloy matrix. [ABSTRACT FROM AUTHOR]

To understand Si precipitation and its influence on mechanical property improvement in high pressure die casting (HPDC) Al9Si3CuFe alloy under direct ageing heat treatment, the precipitates in Al9Si3CuFe alloy containing in-situ MgAl 2 O 4 particles is analyzed via atomic-resolution scanning transmission electron microscopy. It is shown that lath-like Si precipitates form in an average size of 50 nm in length, and a good orientation relationship of {010}<001> Al //{111}<01–1> Si is observed between Si precipitate and matrix. Interestingly, Cu and Zn are observed to segregate onto Si/Al interface, which has a coarsening resisting effect on precipitate growth. The presence of these Si precipitates is the main factor contributing to the further improvement of mechanical properties of Al9Si3CuFe alloy, which results in an increase of 70 MPa in yield strength compared to the alloy without Si precipitates. • Cu and Zn are observed to segregate onto Si/Al interface. • The segregation has a coarsening resisting effect on Si precipitate growth. • The presence of Si precipitates results in a further improvement of 70 MPa in yield strength. [ABSTRACT FROM AUTHOR]