Abstract
This paper identifies the mechanisms of phase and structural transformations during severe plastic deformation by shearing under pressure (high-pressure torsion) of an Al-Zn-Mg-Fe-Ni-based aluminum alloy depending on different initial states of the material (an ingot after homogenizing annealing and a rod produced by radial-shear rolling). Scanning and transmission electron microscopy are used to determine the morphological and size characteristics of the structural constituents of the alloy after high-pressure torsion. It has been found that, irrespective of the history under high-pressure torsion, fragmentation and dynamic recrystallization results in a nanostructural alloy with a high microhardness of 2000 to 2600 MPa. Combined deformation processing (high-pressure torsion + radial-shear rolling) is shown to yield a nanocomposite reinforced with dispersed intermetallic phases of different origins, namely Al9FeNi eutectic aluminides and MgZn2, Al2Mg3Zn3, and Al3Zr secondary phases. The results of uniaxial tensile testing demonstrate good mechanical properties of the composite (ultimate tensile strength of 640 MPa, tensile yield strength of 628 MPa, and elongation of 5%).
Highlights
The results have shown that the principal mechanisms of structure formation in a 7xxx series alloy under high-pressure torsion (HPT) remain the same, but the presence of Al9 FeNi eutectic aluminides in the composite structure affects the morphology and kinetics of the precipitation of secondary phases and increases the thermal stability of the composite and its strength
It has been found that severe plastic deformation is accompanied by the formation of a high-strength (Hv = 2000 to 2600 MPa) aluminum-matrix composite reinforced with dispersed intermetallic compounds of different origins
Eutectic aluminides break down into micron-sized fragments and become uniformly distributed in the volume; the strengthening phases precipitate in the form of globules on the grain boundaries and inside the matrix grains
Summary
Aluminum-matrix composite materials reinforced with silicon carbide are used in automobile industry, aerospace engineering and other industries owing to high wear resistance, high specific strength, and heat conductivity [5,6,7]. It was shown that silicon carbide reinforced aluminum matrix composites are effectively alloyed with the chromium [8]. Besides artificial composites, which are produced by mechanical alloying or by powder metallurgy, there is a big class of natural aluminum-based eutectic composite materials. Typical examples of such alloys are represented by Al-Si alloys (silumins). New advanced alloys based on Al-Fe, Al-Ni, and Al-Fe-Ni eutectics have lately been developed and termed nickalins [9,10,11]
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