Marat Gazizov

Effect of Cold Plastic Deformation Prior to Ageing on Creep Resistance of an Al-Cu-Mg-Ag Alloy

Effect of thermomechanical processing on creep resistance at 150°C of an Al-5.6Cu-0.72Mg-0.5Ag-0.32Mn-0.17Sc-0.12Zr (wt. %) alloy was examined. It was shown that increasing strain prior to artificial aging provides achieving high strength. However, a degradation of the creep resistance, i.e., significant decrease in the rupture time and increase in the minimal creep rate, took place, concurrently. The effect of cold rolling on the strength and creep resistance is discussed in relation with the strain effect on the dispersion of secondary phases. The increase in strength and degradation of creep properties of the alloy subjected to cold working before ageing result from superposition of two competitive processes. First, an increase in the lattice dislocation density facilitates the precipitation of Ω-phase plates with high aspect ratio, leading to increase in the static strength at room temperature. Second, acceleration of the diffusion processes results in coarsening of strengthening phase in grain/subgrain interiors and precipitation of Ω-phase on deformation-induced boundaries during creep that deteriorates creep resistance.

The Role of Deformation Banding in Grain Refinement under ECAP

The mechanism of grain refinement in an Al-5.4Mg-0.4Mn-0.2Sc-0.09Zr alloy subjected to equal-channel angular pressing (ECAP) at 300°C through route BC is considered. It was shown that the formation of geometrically necessary boundaries (GNB) aligned with a {111} plane at ε≤1 initiates the occurrence of continuous dynamic recrystallization (CDRX). Upon further strain the GNBs transform to low-to-moderate angle planar boundaries that produces lamellar structure. In the strain interval 2-4, 3D arrays of planar boundaries evolve due to inducing the formation of 2nd order and higher orders families of GNBs in new {111} planes. GNBs gradually convert to high-angle boundaries (HAB) with strain. A uniform recrystallized structure is produced at a true strain of ∼8. The role of slip concentration and shearing patterns in the formation of GNBs is discussed.

Effect of Cold Plastic Deformation on Mechanical Properties of Aluminum Alloy 2519 After Ageing

Effect of cold plastic deformation prior to ageing at 180°C on a microstructure and mechanical properties at room temperature for an AA2519 alloy was examined subjected to solution treatment and water quenching initially. It was found that cold rolling with a reduction of 15% or equal-channel angular pressing (ECAP) up to a true strain of ~1 leads to acceleration of age-hardening response of this alloy. Peak hardness values of 127, 175 and 169 HV0.2 were achieved by ageing following quenching, cold rolling and ECAP, respectively. The highest values of yield stress (YS) of 475 MPa and ultimate tensile strength (UTS) of 520 MPa, were attained after ECAP followed by ageing. The effect of cold plastic deformation prior to ageing on the precipitation behavior and its relation with mechanical properties of the AA2519 is discussed.

Superplasticity of an AA2519 Aluminum Alloy

A commercial AA2519 alloy with a chemical composition of Al-5.64Cu-0.33Mn-0.23Mg-0.15Zr (in wt. %) was subjected to two-step thermomechanical processing (TMP) providing the formation of fully recrystallized structure with an average grain size of ~7 mm in 3 mm thin sheets. Superplastic tensile tests were performed in the temperature interval 450-535°C and initial strain rates ranging from ~2.8 x 10-4 to ~6.0 x 10-1 s-1. The highest elongation-to-failure of ~750% appears at a temperature of ~525°C and an initial strain rate of ~1.4 × 10-4 s-1 with the corresponding strain rate sensitivity coefficient of ~0.46.

Effect of Annealing on Structure and Mechanical Behavior of an AA2139 Alloy

An AA2139 alloy with a chemical composition of Al–4.35Cu-0.46%Mg–0.63Ag-0.36Mn–0.12Ti (in wt.%) and an initial grain size of about 155 μm was subjected to annealing at 430°C for 3 h followed by furnace cooling. This treatment resulted in the formation of a dispersion of coarse particles having essentially plate-like shape. The over-aged alloy exhibits lower flow stress and high ductility in comparison with initial material in the temperature interval 20-450°C. Examination of microstructural evolution during high-temperature deformation showed localization of plastic flow in vicinity of coarse particles. Over-aging leads to transition from ductile-brittle fracture to ductile and very homogeneous ductile fracture at room temperature.

Effect of ECAP Prior to Aging on Microstructure, Precipitation Behaviour and Mechanical Properties of an Al-Cu-Mg Alloy

Microstructure, precipitation behaviour and mechanical properties of an Al-5.64Cu-0.33Mn-0.23Mg-0.14Zr-0.11Ti (in wt. %) alloy subjected to thermomechanical processing (TMP) involving equal-channel angular pressing (ECAP) at ambient temperature to total strains (ε) of ~1 and ~2 followed by aging at 180°C for 0-28 h have been investigated and compared with conventional aging at the same temperature (T6 state). TMP led to significant increase in yield stress (YS) and ultimate tensile strength (UTS) and decrease in elongation-to-fracture as compared to the peak-aged T6 state. The YS, UTS and δ values attained after ECAP to ε ~ 2 followed by peak ageing were ~510 MPa, ~540 MPa and ~7.6%, respectively. The changes in mechanical properties were related to microstructure evolution and precipitation behaviour. TMP conditions obtaining a high-strength state of the Al-Cu-Mg alloy are discussed.

High cyclic fatigue performance of Al–Cu–Mg–Ag alloy under T6 and T840 conditions

Abstract High cyclic fatigue (HCF) behavior of an AA2139 alloy belonging to Al–Cu–Mg–Ag system in T6 and T840 conditions was examined. The T840 treatment involving cold rolling with a 40% reduction prior to peak ageing provides an increase in tensile strength compared with the T6 condition. However, fatigue lifetime for two material conditions was nearly the same since there is weak effect of thermomechanical processing on micro-mechanisms of crack initiation and growth.

Crack Resistance of an Alloy of the Al – Cu – Mg – Ag System

Cyclic crack resistance of an aluminum alloy of the Al – Cu – Mg – Ag system with a high content of doping elements is studied. It is shown that the alloy possesses a high threshold value of the stress intensity factor for nucleation of fatigue cracks. However, the nonuniform distribution of second-phase particles in the material reduces the crack resistance. Special features and main differences of the relief of fatigue fracture surfaces of the alloy in various regions of the kinetic diagram are considered. Coefficients of the Paris’ equation for the region of linear fatigue-crack growth are determined.

Mechanism of Grain Refinement during Equal-Channel Angular Pressing at Intermediate Temperature in an Al-Mg-Sc Alloy

The mechanism of grain refinement of an Al-5.4Mg-0.4Mn-0.2Sc-0.09Zr alloy subjected to equal-channel angular pressing (ECAP) with a back pressure (BP) for up to 12 passes via route BC at 573K (300 °C) was studied. New grains form through a specific mechanism of continuous dynamic recrystallization (CDRX). At the first pass of ECAP, formed geometrically necessary boundaries play a vital role in initiation of recrystallization process due to formation of planar lamellar structure. The second pass led to transformation of this planar to 3D net of sub-boundaries which are changes into high-angle boundaries at further deformation. The formation of primary MSBs is associated with the appearance of texture a-fiber, and the appearance of a new type of shear texture, which is an axial {112} texture of orientation around the transverse direction accompanies the formation of ultra-fine grains.

Superplastic Behavior of an AA2139 Subjected to ECAP

An AA2139 alloy belonging to Al-Cu-Mg-Ag system was subjected to thermomechanical processing (TMP) included solution treatment at 525°C for 1 h, quenching in water, over-aging at 380°C for 3 h followed by equal-channel angular pressing (ECAP) at 250°C to a total strain of ~12 via route BC. This TMP produced a partially recrystallized structure with fine crystallites having an average size of ~0.9 μm and a fraction of high-angle boundaries of ~56%. Tensile test was performed in the temperature interval 300-500°C at initial strain rates ranging from ~1.8×10-4 to ~1.7×10-1 s-1. It was shown that the highest elongation-to-fracture of ~660% appears at a temperature of 400°C and an initial strain rate of 1.4×10-3 corresponding with the coefficient of sensitivity coefficient, m, of 0.34.