Nanostructure Characteristics of Al3Sc1−xZrx Nanoparticles and Their Effects on Mechanical Property and SCC Behavior of Al–Zn–Mg Alloys

The Nanostructure characteristics of Al3Sc1−xZrx nanoparticles and their effects on the mechanical properties and stress corrosion cracking (SCC) behavior of Al–Zn–Mg alloys were investigated by 3D atom probe analyses, high-angle annular-dark-field scanning transmission electron microscopy methods, electron back scattered diffraction techniques, electrochemical measurements, slow strain rate tests and quantitative calculations. The results show that adding small amounts of scandium (0.10 percent by weight) and zirconium into Al–Zn–Mg extrusion bars can precipitate Al3Sc1−xZrx nanoparticles with a number density of (7.80 ± 3.83) × 1021 per cubic meter. Those particles, with a low lattice misfit with matrix (1.14 ± 0.03 percent) and stable core-shell L12-nanostructure in aged Al–Zn–Mg alloys, can increase the yield strength by 161 ± 7 MPa via strong Orowan strengthening (the theoretical calculated value is 159 MPa) and weak Hall-Petch strengthening (the theoretical calculated value is 6 MPa). Moreover, Al3Sc1−xZrx nanoparticles can change the fracture mechanism of alloys in 3.5% NaCl solution from intergranular cracks to transgranular failure, and decrease the proportion of high-angle grain boundaries from 87% to 31%, thus reducing the microchemistry differences around the grain boundaries and anodic dissolution kinetics, and improving intergranular SCC resistance and ductility. This study offers a new approach to the simultaneous improvement in mechanical property and corrosion performance of high strength alloys.

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Precipitation on Low Angle Boundaries in Al-Zn-Mg

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s1431927600001574 ◽

1980 ◽

Vol 38 ◽

pp. 374-375

Author(s):

Diane M. Vanderwalker

Keyword(s):

Grain Boundaries ◽

High Strength ◽

Boundary Structure ◽

Aircraft Industry ◽

Precipitate Free Zone ◽

High Angle ◽

Adjacent Region ◽

Free Zone ◽

Widespread Interest

There is a widespread interest in understanding the properties of Al-base alloys so that progress can be made toward extending their present applications in the aircraft industry. Al-Zn-Mg is precipitation hardened to gain its high strength; however, during aging the formation of heterogeneous precipitates on the grain boundaries creates a precipitate-free zone in the adjacent region. Since high angle grain boundaries are not easily characterized, it is difficult to establish a relationship between the precipitate and the boundary structure. Therefore, this study involves precipitation on low angle grain boundaries where the boundary and the precipitate can be fully analyzed.

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FEI Tecnai G2 F20

Journal of large-scale research facilities JLSRF ◽

10.17815/jlsrf-2-138 ◽

2016 ◽

Vol 2 ◽

Cited By ~ 24

Author(s):

Martina Luysberg ◽

Marc Heggen ◽

Karsten Tillmann

Keyword(s):

Scanning Transmission Electron Microscopy ◽

Dark Field ◽

Conventional Imaging ◽

Electron Loss ◽

High Angle ◽

X Ray ◽

Transmission Electron ◽

Scanning Transmission ◽

Set Up ◽

Elemental Maps

The FEI Titan Tecnai G2 F20 is a versatile transmission electron microscope which is equipped with a Gatan Tridiem 863P post column image filter (GIF) and a high angle energy dispersive X-ray (EDX) detector. This set up allows for a variety of experiments such as conventional imaging and diffraction, recording of bright- and dark-field scanning transmission electron microscopy (STEM) images, or acquiring elemental maps extracted from energy electron loss spectra (EELS) or EDX signals.

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