In recent years, much progress has been made in the studies of nanostructured Al alloys for advanced structural and functional use associated both with the development of novel routes for the fabrication of bulk nanostructured materials using severe plastic deformation (SPD) techniques and with investigation of fundamental mechanisms leading to improved properties. This review paper discusses new concepts and principles in application of SPD processing to fabricate bulk nanostructured Al alloys with advanced properties. Special emphasis is placed on the relationship between microstructural features, mechanical, chemical, and physical properties, as well as the innovation potential of the SPD-produced nanostructured Al alloys.

Nanostructured aluminium alloys produced by severe plastic deformation: New horizons in development

There are several modeling methods available for predicting the strength of metal matrix nanocomposites Among these, Zhang and Chen approach and Clyne method predict closer results to experimental values However, in Zhang and Chen method, the effect of Hall–Petch strengthening is neglected which results in less precision of the results In this study, the effects of all active strengthening mechanisms including Hall–Petch, Orowan, CTE mismatch and load bearing are considered, by using Clyne approach The results are in good agreement with experimental data and more precise than those from other models Furthermore, studies on different strengthening mechanisms showed that Hall–Petch strengthening mechanism is the most important factor, which should not be neglected even in micro-scale grain size

Comparison between current models for the strength of particulate-reinforced metal matrix nanocomposites with emphasis on consideration of Hall–Petch effect

Surface composites by friction stir processing: A review

Friction stir welding/processing of metals and alloys: A comprehensive review on microstructural evolution

Influence of grain size and texture on Hall–Petch relationship for a magnesium alloy

The 7XXX series age-hardenable high-strength aluminum alloys find useful applications in the field of aerospace engineering. Constant efforts are being made to tailor the mechanical and corrosion properties of these alloys as per requirements for a particular application. These properties are a function of factors like microstructure, chemical composition and processing parameters. An effort has been made to collate the information available from different studies conducted on alloys Al 7050 and Al 7055. Databases were created to consolidate the information about microstructure, mechanical properties and corrosion behavior for the two alloys. Existing models were utilized to predict strength and fracture toughness for these alloys and these models were validated using experimental values and a qualitative evaluation was made for the corrosion behavior of these alloys. Available data were utilized to prepare maps that are intended to serve as guides to design aluminum alloys with desired combination of properties.

Structure-property correlations in Al 7050 and Al 7055 high-strength aluminum alloys

The mechanical behavior of ultrafine grained AA5052 processed through different techniques—rolled, annealed, friction stir processed (FSP) and equal channel angular pressed (ECAP)—were compared and correlated with microstructure. The microstructure was characterized using electron back scattered diffraction to obtain the boundary spacing, the fraction of high angle boundaries and to estimate the dislocation density from local misorientations. Both FSP and ECAP conditions had ultrafine boundary spacing, but the fraction of high angle boundaries was larger for the FSP condition. Tensile deformation carried out at 297 K and 10−3 s−1 showed a lower work-hardening rate and recovery rate for FSP as compared to the ECAP condition. It was inferred that low angle boundaries are more effective sinks for dislocations. When comparing differently processed materials, the strength, ductility and work-hardening behavior correlate better with the fraction of high angle boundaries than the boundary spacing.

Influence of fraction of high angle boundaries on the mechanical behavior of an ultrafine grained Al–Mg alloy

Twin-roll cast (TRC) Al–Mg–Sc alloy was friction stir processed (FSP) to obtain ultrafine grained (UFG) microstructure. Average grain size of TRC alloy in as-received (AR) condition was 19.0 ± 27.2 μm. The grain size reduced to 0.73 ± 0.44 μm after FSP. About 80% of the grains were smaller than 1 μm in FSP condition. FSP resulted into 80% of the grain boundaries to have high angle grain boundary (HAGBs) character. Uniaxial tensile testing of UFG alloy showed an increase in yield strength (YS) and ultimate tensile strength (UTS) (by ∼100 MPa each) of the alloy with a very marginal decrease in total and uniform elongation (total – 27% in AR and 24% in UFG and uniform – 19% in AR and 14% in UFG). A theoretical model predicted that the grain refinement cannot take place via discontinuous dynamic recrystallization. Zener pinning model correctly predicted the grain size distribution for UFG alloy. From work hardening behaviors in both the conditions, it was concluded that grain boundary spacing is more important than the character of grain boundaries for influencing extent of uniform deformation of an alloy.

Microstructure and Mechanical Behavior of Friction Stir Processed Ultrafine Grained Al-Mg-Sc Alloy

Critical grain size for change in deformation behavior in ultrafine grained Al–Mg–Sc alloy

This chapter describes the metallurgy of ultrahigh strength (UHS) steels used in airframe structures, particularly for landing gear components, for which medium carbon, low alloy steels have been the dominant materials. High alloy steels exhibiting better toughness and corrosion resistance are used for structures operating under more demanding loading conditions and environments such as in aircraft carriers. Steels are unique from the perspective of being in use significantly longer than any other metallic structural material and yet, being the first family of airframe alloys to be successfully designed computationally and commercialized, still provide significant opportunities for property enhancement. In the framework of the composition–microstructure–processing–properties relationships, the discussion in this chapter is limited to how UHS steels used in airframe structures have evolved historically, the metallurgy and mechanisms underlying their behavior, and how this knowledge has been applied to new alloy design.

Krishnan K. Sankaran

Papers

Structure-property correlations in Al 7050 and Al 7055 high-strength aluminum alloys

Influence of fraction of high angle boundaries on the mechanical behavior of an ultrafine grained Al–Mg alloy

Microstructure and Mechanical Behavior of Friction Stir Processed Ultrafine Grained Al-Mg-Sc Alloy

Critical grain size for change in deformation behavior in ultrafine grained Al–Mg–Sc alloy

Ultrahigh Strength Steels