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Microstructure evolution of an Al-0.4Zr(wt.%) alloy after isothermal aging (AG) and subsequent high pressure torsion (HPT) and its impact on strength and electrical conductivity has been investigated. Microstructure was characterized by X-ray diffraction, electron backscatter diffraction, transmission electron microscopy (TEM) and electron energy-dispersive X-ray spectroscopy in TEM. The initial Al-0.4Zr(wt.%) alloy obtained by combined casting and rolling presents solid solution of Zr in Al matrix. Aging at 375 °C for 60 h leads to formation of uniformly distributed metastable Al3Zr precipitates with the average diameter of 13 nm, resulting thereby in a decrease of strength sUTS from 128 to 95 MPa and in increase of conductivity from 50.7 to 58.8% IACS at ambient temperature. The subsequent HPT processing leads to grain refinement and partial dissolution of the Al3Zr precipitates that is accompanied by enrichment of solid solution by Zr atoms and by coarsening of the remaining Al3Zr precipitates. The combination of AG and HPT provides the strength and the conductivity at ambient temperature which do not decrease under annealing up to 230 °C. Moreover, additional strengthening accompanied by an increase in conductivity was found for AG-HPT samples after annealing at Tan=230 °C for 1 h, that provides the best combination of the strength of sUTS=142 MPa and the conductivity of 58.3% IACS. Contribution of different possible mechanisms into strength and charge scattering are analyzed on the basis of specific microstructural features. The analysis indicates a suppression of strengthening by the Orowan mechanism in AG and AG-HPT samples. In all the studied states, i.e. initial, after AG, and subsequent HPT, grain boundary strengthening is found to be the main strengthening mechanism.

This work focuses on the effect of high pressure torsion (HPT) on the thermostability, microstructure, mechanical properties and electrical conductivity of an Al–8.5 wt.% RE (RE stands for rare earth Ce and La in the present case) alloy with respect to its potential application in electrical engineering. HPT processing leads to the formation of a very homogeneous ultra-fine grained microstructure resulting from the fragmentation of RE-rich intermetallic particles down to the nanoscale. Deformation induced supersaturated solid solution of RE atoms in the Al matrix is demonstrated for the first time. The HPT processed material shows an extraordinary high mechanical strength attributed to the high volume fraction of nanoscaled intermetallic particles and the ultrafine grained (UFG) microstructure. The various strengthening contributions were analyzed, and it was shown that the increase of strength during short time annealing could be attributed to the clustering of RE atoms in solid solution. The HPT processing induces a significant reduction of the electrical conductivity, but it was partly restored by annealing thanks to the concomitant clustering of RE atoms, reduction of dislocation density and grain growth. The potential applications of UFG Al–RE alloys in electrical engineering are finally discussed. [ABSTRACT FROM AUTHOR]

The melting of coarse- and fine-grained Al–Mg alloys was studied by the differential scanning calorimetry (DSC). The transition from incomplete to complete wetting of grain boundaries (GBs) takes place in binary Al–Mg alloys. The heat effect of GB wetting manifests itself in the asymmetric shape of the DSC melting curve. By decreasing grain size (and increasing specific area of GBs) the GB “shoulder” in DSC curve becomes more pronounced. Basing on DSC data, the position of GB solidus (or premelting) line for Al–Mg alloys has been estimated. Contrary to the Al–Zn alloys, the difference between bulk and GB solidus does not exceed 2 °C. [ABSTRACT FROM AUTHOR]

The contribution of ultrafine grains and nanoscaled precipitates has been investigated in the Al–Mg–Si system to optimize the combination of strength and electrical conductivity. A full range of nanoscaled structures was achieved by varying severe plastic deformation and post-processing precipitation treatments. Nanoscaled features, like grain size, solute content of the matrix, precipitate size, density or distribution were quantitatively estimated by analytical transmission electron microscopy and atom probe tomography. Deformation induced precipitation and grain boundary segregations are reported here and the physical origins are discussed. The concomitant grain growth and precipitation mechanisms that occur during post deformation aging treatment have also been investigated. Then, the quantitative data obtained from the nanoscale characterization of ultrafine grain structures allowed adjusting physical models to account both for the mechanical strength and the electrical conductivity. Based on this approach, the range of properties achievable in Al–Mg–Si alloys was estimated. [ABSTRACT FROM AUTHOR]

• UFG Al-Cu-Zr alloy was produced by high pressure torsion. • Annealing followed by straining notably increased plasticity preserving high strength. • This effect is related to changes in dislocation structure of grain boundaries. • Segregation in GBs can influence deformation mechanisms in the UFG alloy. We study the effect of annealing followed by additional deformation on the mechanical performance of an ultrafine-grained Al-Cu-Zr alloy with a mean grain size of 300 nm. We show that elongation to failure can be notably increased by modification of the alloy's defect structure and discuss this phenomenon in terms of interfacial dislocation emission and interaction of dislocations with grain boundaries in different states. [ABSTRACT FROM AUTHOR]

Abstract: A coarse-grained (CG) Al6061 alloy after solution treatment is subjected to high pressure torsion at room temperature resulting in the formation of a homogeneous ultra-fine grained (UFG) microstructure with average grain size of 170nm. Tensile tests are performed at room and liquid nitrogen temperatures for both CG and UFG conditions. Analysis of the surface relief of the tested specimens is performed. The effect of microstructure on the mechanical properties and on the deformation behavior of the material is discussed. [Copyright &y& Elsevier]