Recent advances in ageing of 7xxx series aluminum alloys: A physical metallurgy perspective

The formation and growth of the magnesium-rich s phase, Al3Mg2, in Al-5083 has been studied by transmission electron microscopy (TEM). The s phase forms heterogeneously both at grain boundaries, and on preexisting particles which are enriched in manganese. The s precipitates at grain boundaries, containing a high density of very fine faults, thicken faster than the rate estimated assuming volume diffusion controlled growth of planar interfaces. It is suggested that pipe diffusion through dislocations contributes to the enhanced growth rate.

Precipitation behavior of the ß phase in Al-5083

Study of the constitutive behavior of 7075-T651 aluminum alloy

The fine-scale microstructure of an Al 5083 alloy sensitized at 373 K (100 °C) for 3, 7, 14, 30, 45, and 90 days has been investigated using transmission electron microscopy (TEM) to study the evolution of the β phase (Al3Mg2) at grain boundaries. In fully sensitized Al 5083, the β phase (Al3Mg2) mostly forms heterogeneously at grain boundaries. TEM observations showed that the grain boundary precipitation of β phase was discrete up to 14 days of aging, and grain boundaries were fully covered by the β phase after 30 to 45 days of aging. The early stages of β growth on the grain boundaries are consistent with the collector-plate mechanism. We find no evidence of either Mg depletion or segregation at the grain boundaries. The initial growth rates as well as the thicknesses after long aging times are greater than can be accounted for by bulk diffusion of Mg to the grain boundaries. We suggest that dislocation pipe diffusion is necessary to account for the β growth rates.

Transmission Electron Microscopic Investigations of Grain Boundary Beta Phase Precipitation in Al 5083 Aged at 373 K (100 °C)

This is a comparative study on the effects of bulk plastic deformation and surface-induced plastic deformation on the fatigue, corrosion behaviour and corrosion fatigue of AA5083. Bulk severe plastic deformation was performed through rotary swaging, whereas surface-induced plastic deformation was conducted by applying shot peening and ball-burnishing. Surface and near-surface properties such as surface topography, microhardness and residual compressive stresses were documented. In comparison to the as-received reference condition, results of potentiodyanmic polarization referred to a better corrosion resistance of the rotary swaged material, while both shot peening and ball-burnishing led to deterioration in corrosion resistance. It was found that, pitting corrosion occurred around Fe-rich intermetallic particles. Ball-burnishing led to superior fatigue performance in air and under corrosive environment in comparison to other investigated conditions.

Investigating the effects of bulk and surface severe plastic deformation on the fatigue, corrosion behaviour and corrosion fatigue of AA5083

The technology required for the design, fabrication, operation, and maintenance of aluminum structures for ships and craft is reviewed to assess the needs for improvements in that technology. The areas reviewed are material property and behavior, structural design, structural details, welding and fabrication, joining aluminum to steel, residual stresses and distortion, fatigue design and analysis, fire protection, vibration, maintenance and repair, mitigating slam loads, and emerging technologies.

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Research needs in aluminum structure

Offshore wind energy is developing rapidly in the United States, particularly off the East coast, which has an extensive continental shelf and where the water depths are such that monopile wind turbines founded directly on the seabed are the most attractive. In a previous paper, the authors demonstrated how the design of a monopole for a 15-MW turbine can be optimized to survive hurricane conditions using several commercially available design tools. This paper extends the study to address multiple loading conditions, including operational working conditions. To do that, different optimizations were run in parallel to find a global solution for multidisciplinary optimization. In the previous study, three independent design tools were used: Wind-plant Integrated System Design and Engineering Model (WISDEM) which was developed by the National Renewable Energy Laboratory (NREL), ANSYS Workbench, a finite element analysis program commonly used in the industry, and the ModeFRONTIER integration platform. To simulate the additional loading conditions, the OpenFAST software from NREL is now included in the workflow to estimate the loads in the different conditions examined.

Robert A. Sielski

Papers

Research needs in aluminum structure

Optimum Design of Extra-Large Wind Turbine Monopile Covering Multiple Conditions