Search

In this work, the influence of the crystallographic orientation of high-purity aluminum single crystals of grade A999 on the transformation of the initial structure as a result of exposure to shock waves at a temperature of −196°C was experimentally investigated. It was found that when the shock front propagates in the [110] direction at pressures of 40 GPa and 50 GPa, structural changes in aluminum single crystals are observed in the form of dislocation slip lines along the (111) and (110) planes. The impact of the shock front in the direction of [113] at a pressure of 50 GPa leads to coordination structural changes. It was found that a nanocrystalline structure with an average grain size of 80 nm is formed in the near-surface layers at a depth of 1–3 mm, and a subgrain structure is formed at a depth of 6–7 mm. In fact, a gradient type structure is formed. The reasons for the pronounced effect of the influence of the crystallographic orientation of high-purity aluminum single crystals on structural changes under the action of shock waves are discussed.

Equal-channel angular pressing was used to process a commercial 1421 aluminum alloy at temperatures from 340 to 410 °C. An optimum ultrafine microstructure was achieved after pressing at 370 °C with an equiaxed grain size of ∼0.3–0.4 μm. Tensile testing showed this material is superplastic at 400 °C with elongations up to ∼1500%. Offsets in surface marker lines demonstrate grain boundary sliding is the dominant flow process.

Equal-channel angular (ECA) pressing is a processing procedure which subjects a material to severe plastic deformation. Tests were conducted on a commercial cast aluminum alloy to evaluate the properties associated with samples subjected to three different ECA pressing procedures. The results show that all three procedures lead to an ultrafine microstructure and each procedure is capable of producing samples which exhibit high strain rate superplasticity. Optimum superplastic properties were achieved in samples subjected to ECA pressing to a strain of ∼12. Under these conditions, the measured elongations to failure at a temperature of 673 K were 1210 and 950% at strain rates of 10−1 and 1 s−1, respectively.

A submicrometer-grained (SMG) Al−3% Mg solid solution alloy, with an initial grain size of ∼0.2 μm, was produced by intense plastic straining. Experiments show that tensile specimens of the SMG alloy exhibit high elongations to failure at low testing strain rates at the relatively low temperature of 403 K. The stress exponent is high (∼7–8) and calculations show deformation is within the region of power-law breakdown. The initial microstructure of the alloy consists of diffuse boundaries between highly deformed grains. At strain rates of ∼10−4 s−1 and lower, plastic deformation leads to dynamic recrystallization and the formation of highly nonequilibrium grain boundaries that gradually evolve into a more equilibrated configuration.

The peculiarities of a submicron-grained structure formation in a series of aluminium- and magnesium-based alloys by means of a special strain-heat treatment are examined in this paper. The unusual mechanical properties of alloys displayed in this state at room temperature as well as at enhanced temperatures are found. The nature of the plastic deformation of these materials is discussed.