D. V. Lotsko

Low Temperature Mechanical Properties of Scandium-Modified Al-Zn-Mg-Cu Alloys

Abstract : Tensile properties of three wrought alloys, (1) Al-10Zn-3Mg-1.2Cu-0.15Zr, (2) Al-10Zn-3Mg-1.2Cu-0.15Zr-0.39Mn-0.49Sc, and (3) Al-12Zn-3Mg-1.2Cu-0.15Zr-0.39Mn-0.49Sc were studied in T6 and T7 conditions at 298K and 77K. The properties depended on the alloy compositions and heat treatment conditions. An increase in the concentration of Zn increased strength and decreased ductility. An addition of Sc increased both strength and ductility. The alloys showed very high strength both at room and cryogenic temperatures. In the T6 condition, the following properties were obtained at room temperature: YS = 760 to 805 MPa, UTS = 770 to 810 MPa, El = 3 to 9%. When the temperature was decreased to 77K, strength increased while elongation decreased, and their values were YS = 1005 to 1065 MPa, UTS = 1010 to 1065 MPa, El = 0.3 to 0.7%. Over-aging allowed an increase in elongation to a value as high as 8.5% at the values of YS = 805 MPa and UTS = 835 MPa at the cryogenic temperature. The deformed alloys showed mixed type of fracture. The fraction of the brittle component increased when the temperature decreased. Although they showed high elongation, the alloys in T7 condition fractured predominantly by intergranular mode at the cryogenic temperature.

Twist Extrusion as a Tool for Grain Refinement in Al-Mg-Sc-Zr Alloys

Al-Mg-Sc-Zr alloys are attractive materials for aircraft and marine applications and have very good potentials for mechanical property enhancement by ultrafine grain structuring. The most developed technique for producing nanostructures has been equal channel angular extrusion. In this paper we describe our attempts on refining grain in these alloys by the twist extrusion technique. It was shown that twist extrusion allows to obtain fairly homogeneous structure with grain sizes dav=0.33, 0.08, and 0.65 µm. This structure is thermally stable up to 500°C for 1 hour.

Quasicrystalline Materials. Structure and Mechanical Properties

A brief description of the structure of quasicrystalline materials, their behavior under mechanical load and the mechanism of their high-temperature plastic deformation on the base of literary data are given. Original data about the investigation of the deformation of AlCuFe quasicrystal by a complex of micro- and nanoindentation techniques in a wide temperature interval are presented.

Structure and hardness of sintered Mo-Ni alloys

The authors employ x-ray diffraction and Vickers hardness testing in order to assess the effect of sintering on the microstructure, lattice parameters, porosity, and hardness of Mo-Ni alloys as well as the metallurgical influence of varying nickel content on these properties.

Structure and High-Temperature Properties of the Alloyed Quasicrystalline Al-Cu-Fe Powders and Thermal-Sprayed Coatings from Them

A structure and some properties of icosahedral quasicrystalline phase Al-Cu-Fe may be increased by directly alloying. Sc and Cr were selected as the alloying elements. The following composition were investigated: AlMCu2<,Fe12, Al62.73Cu25Fe12Sco.27, Al62.5f,Cu2.,Fe12Sc0.44, Al M > CU| X Fe 8 Cr 8 . The powders were fabricated by melt atomization with high-pressure water. The thermal-sprayed coatings were manufactured from powders of the size fraction of (-63+40) pm. It is established that alloying of the quasicrystalline Al-Cu-Fe alloy with scandium in the amount of 0.265 and 0.44 at. % increases the content of the quasicrystalline icosahedral ψ-phase in powders and coatings. Thus, in the powder of (-63+40) pm size fraction the ψ-phase content increased to 60-65 wt. % compared to 55 wt. % in the non-alloyed powder. The thermal treatment of powders and coatings with scandium provided a reliable possibility to obtain a 100 % ψ-phase content. In Al-Cu-Fe-Sc powders a singlephase ψ-state was obtained by annealing for 1 h at 650°C, whereas in the case of Al-Cu-Fe powders annealing at 700 °C was required. The annealing of AlCu-Fe-Cr powders at 600 °C results in formation of approximant phase (O, -phase) . The thermal-sprayed coating from Al-Cu-Fe powder has microhardness of about 6 GPa at room temperature, which hardly changes at 300 °C, whereas with further heating it gradually falls to a level of about 3 GPa at 600 °C. Alloying with Sc and Cr did not essentially change the temperature dependence of the hardness of coatings from the non-alloyed alloy.

Influence of Scandium on Amorphization of Aluminum Alloys

Structure of Al100−xScx, Al91Ce9−xScx, and Al85Ni10Ce5−xScx alloys manufactured in the form of melt-spun ribbons was investigated in order to establish the influence of scandium on the tendency to amorphization of aluminum alloys alloyed with rare-earth metals. Ribbons structure was compared with their hardness. Thermal stability of ribbon structure was studied.

Structural distortions in the surface layer of single-crystal molybdenum after face grinding

Use of diamond grinding wheels with organic and ceramic bonds makes it possible to avoid the phenomenon of wheel glazing during fine grinding of molybdenum single crystals and to obtain a high quality ground surface with the minimum level of structural distortions. The nature of the orientation dependence of surface structural distortions is established by studying {001}, {110}, and {111} molybdenum single crystals. This is connected with features of plastic deformation during grinding.

Consolidation of Al-Cu-Fe Powders with Quasicrystalline Components by Using High Quasihydrostatic Pressures

The technique of powder consolidation under a high quasi-hydrostatic pressure was used for consolidating quasicrystalline AlCuFe powders manufactured by water-atomization technique. The optimum conditions for the consolidation were selected through the analysis of the dependence of sample porosity on pressure and temperature in various stages of the consolidation process. The consolidation process took 2–3 min. X-ray investigation of sintered samples was performed, their hardness was measured. A softening of samples with the growth of pressure was revealed, which was interpreted as the influence of phason defects created by deformation while consolidation.

Effect of Fe and Si on the Structure and Mechanical Properties of Complex Al-Zn-Mg-Cu Alloys Produced by P/M and Casting Techniques

In order to establish the possibility of using recycled aluminum, which usually has an increased content of Fe and Si, the structure and mechanical properties of high-strength Al-Zn-Mg-Cu alloys additionally alloyed with only Fe and Si as well as additionally alloyed with Mn, Zr, Sc, Fe and Si were studied. Rods were manufactured from ingots cast into water-cooled copper molds as well as by a P/M technique using powders atomized from the melt by high-pressure water. The microstructure and distribution of elements in the starting condition and in the T6 treated extruded rods were studied by OM and SEM techniques and compared with rod tensile properties. An addition of Fe up to 1 wt.% led to a 5–7% increase in strength. This increase was accompanied by a decrease in ductility in the cast and cast-and-wrought alloys. In alloys prepared by P/M the technique, the addition of Fe led to about 20% increase in strength, as compared to the baseline alloy, without any detrimental effect on elongation. An addition of ≥0.5 wt.% Si to the P/M alloys decreased strength and slightly increased ductility. Thus, reasonable properties were obtained in high strength Al-Zn-Mg-Cu alloys containing significant amounts of Fe and Si.

Structure Peculiarities of Al63Cu25Fe12 Ingots with a Quasicrystalline Component

For manufacturing ingots two techniques were used: the technique of drawing the melt into a thin quartz tube; the technique of melting in a copper water-cooled crystallizer. The structural condition of Al63Cu25Fe12 ingots produced with various cooling rates was characterized by the presence of phases i (quasicrystalline), β (bcc of AlFe type), and λ (monoclinic of Al13Fe4 type). The size of phase components lowered with increasing the cooling rate. A single-phase ψ-condition was obtained by annealing at 750 °C.