Search

This work investigates the influence of parameters of initial ultrafine-grained (UFG) structure in commercially pure (CP) Al on annealing-induced hardening (AIH) and deformation-induced softening (DIS) effects. UFG structures were formed via processing CP Al by various methods of severe plastic deformation (high pressure torsion (HPT), equal channel angular pressing (ECAP) and combination of ECAP and cold rolling (CR)). AIH and DIS effects are observed in all the studied UFG structures. However, HPT Al demonstrates large increase of strength due to annealing and drastic gain of ductility after subsequent additional deformation whereas in ECAP Al and ECAP þ CR Al both effects are much less pronounced. Microstructure characterization by X-ray diffraction (XRD) analysis, electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) was performed for HPT Al and ECAP þ CR Al in the three studied states: before and after annealing and after annealing and subsequent additional deformation. Analysis of microstructure evolution during annealing and subsequent additional deformation shows that the key microstructure parameter which is responsible for AIH and DIS effect is the change of dislocation density in grain interior in ECAP þ CR Al, whereas in HPT Al the effects are related to the change of dislocation density at/near grain boundaries. In addition, outstanding combination of high strength (~210 MPa), high electrical conductivity (~62 %IACS) with sufficiently good ductility (7 e10 %) and thermal stability (up to 150°C, at least) was achieved for ECAP þ CR Al after annealing at 150 °C, 1h. [ABSTRACT FROM AUTHOR]

The influence of additional deformation heat treatments (DHTs), implemented by two regimes: (1) annealing and small additional deformation by high-pressure torsion (HPT) at room temperature (RT) and (2) HPT at elevated temperature to 10 turns and small additional HPT at RT, has been studied on the microstructure, mechanical properties and electrical conductivity of ultrafine-grained (UFG) Al-0.53Mg-0.27Zr (wt.%) alloy structured by HPT to 10 turns at RT. As is shown, both types of additional DHT lead to a substantial increase in plasticity (2–5 times) while maintaining high electrical conductivity (~53% IACS) and strength comprising 75–85% of the value in the pre-DHT state of the UFG alloy. The possible physical reasons for the revealed changes in the physical and mechanical properties are analyzed. Comparison of the strength and plasticity changes with the microstructure evolution after DHT of both types indicates that the increase in the density of introduced grain boundary dislocations is the most probable factor providing a tremendous increase in plasticity while maintaining a high level of strength in the UFG alloy under study. An outstanding combination of high strength (370 MPa), high elongation to failure (~15%) and significant electrical conductivity (~53% IACS) was achieved for the Al-Mg-Zr alloy. This combination of properties exceeds those obtained to date for this system, as well as for a number of other commercial conductor alloys based on the Al-Zr system. [ABSTRACT FROM AUTHOR]

The paper reports on the features of low-temperature superplasticity of the heat-treatable aluminum Al-Mg-Si alloy in the ultrafine-grained state at temperatures below 0.5 times the melting point as well as on its post-deformation microstructure and tensile strength. We show that the refined microstructure is retained after superplastic deformation in the range of deformation temperatures of 120–180 °C and strain rates of 5 × 10–3 s–1–10–4 s–1. In the absence of noticeable grain growth, the ultrafine-grained alloy maintains the strength up to 380 MPa after SP deformation, which considerably exceeds the value (250 MPa) for the alloy in the peak-aged coarse-grain state. This finding opens pathways to form high-strength articles of Al-Mg-Si alloys after superplastic forming. [ABSTRACT FROM AUTHOR]

An ultrafine-grained (UFG) Al-4.8%Zn-1.2%Mg-0.14%Zr (wt%) alloy was processed by high pressure torsion (HPT) technique and then aged at 120 and 170 °C for 2 h. The changes in the microstructure due to this artificial aging were studied by X-ray diffraction and transmission electron microscopy. It was found that the HPT-processed alloy has a small grain size of about 200 nm and a high dislocation density of about 8 × 1014 m−2. The majority of precipitates after HPT are Guinier–Preston (GP) zones with a size of ~ 2 nm, and only a few large particles were formed at the grain boundaries. Annealing at 120 and 170 °C for 2 h resulted in the formation of stable MgZn2 precipitates from a part of the GP zones. It was found that for the higher temperature the fraction of the MgZn2 phase was larger and the dislocation density in the Al matrix was lower. The changes in the precipitates and the dislocation density due to aging were correlated to the hardness evolution. It was found that the majority of hardness reduction during aging was caused by the annihilation of dislocations and some grain growth at 170 °C. The aging effect on the microstructure and the hardness of the HPT-processed specimen was compared to that observed for the UFG sample processed by equal-channel angular pressing. It was revealed that in the HPT sample less secondary phase particles formed in the grain boundaries, and the higher amount of precipitates in the grain interiors resulted in a higher hardness even after aging. [ABSTRACT FROM AUTHOR]

This paper reports on a crucial role of the morphology of intermetallic Al 11 RE 3 phase and Al/Al 11 RE 3 interphase (where RE – Rare Earth) surface area, before plastic deformation, on the electrical and mechanical properties and the thermostability of aluminium alloys. Cast Al-4.5 (Ce + La) alloy samples, processed with and without spheroidization treatment (ST), were subjected to high pressure torsion (HPT) at room temperature (RT) followed by annealing at 230 °C, 280 °C and 400 °C for 1 h. It is demonstrated, that the changes of initial alloy structure (particles shape/size) and the decrease of interphase surface area affect the distribution of intermetallic particles after HPT, the distribution of ultrafine grains and the dislocation density, as well as the formation of a supersaturated solid solution of Ce and La in aluminium. The optimal combination of strength (ultimate tensile stress (σ UTS) 430 MPa) and conductivity (55.9% International Annealed Copper Standard, IACS) was obtained after ST, HPT and an annealing temperature of 230 °C. Image 1 • Influence intermetallic morphology on structure and properties of Al alloys is studied. • The alloys were subjected to severe plastic deformation in different initial state. • HPT of Al-4.5(Ce,La) alloy results in supersaturated solid solution formation. • Application of pre-HPT heat treatment prevents the solid solution formation during HPT. • The diffusion of Ce and La in Al is provided by extra vacancy concentration. [ABSTRACT FROM AUTHOR]

This study focuses on the difference in microstructural features and physical properties of Al-2Fe and Al-4Fe alloys subjected to large plastic straining. The difference in the intermetallic particle morphology in the initial state is shown to be a key parameter influencing the particle and grain fragmentation process and, as a result, the properties of these two alloys. We demonstrate that the shape and average size of Al-Fe intermetallic particles provide stronger effect on the microstructure evolution during high pressure torsion (HPT) than their volume fraction. The formation of Fe supersaturated solid solution in Al in these two alloys during deformation is discussed in connection to the morphology of the intermetallic phase. The major microstructural attributes, responsible for the solid solution formation, are highlighted. [ABSTRACT FROM AUTHOR]

This paper focuses on the mechanical properties, electrical conductivity and fatigue performance of ultra-fine-grained (UFG) Al-Mg-Si wires processed by a complex severe plastic deformation route. It is shown that the nanostructural design via equal channel angular pressing (ECAP) Conform followed by heat treatment and cold drawing leads to the combination of enhanced tensile strength, sufficient ductility, enhanced electrical conductivity, and improved fatigue strength compared to the wires after traditional T81 thermo-mechanical treatment used in wire manufacturing. The Processing-microstructure-properties relationship in the studied material is discussed. [ABSTRACT FROM AUTHOR]

• UFG 6060 alloy has σ B = 525 MPa, Hv = 120 at 25 °C. • High ductility 220% is observed at 150 °C and 5 × 10−3 s−1. • UFG alloy retains an increased 80% of level of strength. Ultrafine-grained (UFG) state with a mean grain size of 180 nm was produced in a 6060 alloy of the Al-Mg-Si system by high pressure torsion (HPT). The UFG Al 6060 alloy demonstrated high strength: microhardness of 120 Hv and ultimate tensile stress of 525 MPa at room temperature. The tensile tests were carried out at temperatures 120, 150 and 180 °C with the strain rate 10−2, 5 × 10−3, 10−3, 5 × 10−4 and 10−4 s−1 to determine the best conditions for the manifestation ductility and study of changes in strength of the study material. It established, that the UFG alloy retains an increased 80% of level of strength at room temperature after deformation at elevated temperatures in the temperature range 120–150 °C. The results obtained are compared with changes of the microstructure and strength of the UFG alloy after annealing under similar temperature–time conditions. [ABSTRACT FROM AUTHOR]