Microstructure, microtexture and precipitation in the ultrafine-grained surface layer of an Al-Zn-Mg-Cu alloy processed by sliding friction treatment
TL;DR: In this article, the microstructural and crystallographic features of the sliding friction treatment (SFT) induced surface deformation layer in a 7050 aluminum alloy were analyzed using transmission electron microscopy (TEM) and high angle angular dark field scanning TEM (HAADF-STEM) observations.
Abstract: Precipitate redistribution and texture evolution are usually two concurrent aspects accompanying grain refinement induced by various surface treatment. However, the detailed precipitate redistribution characteristics and process, as well as crystallographic texture in the surface refined grain layer, are still far from full understanding. In this study, we focused on the microstructural and crystallographic features of the sliding friction treatment (SFT) induced surface deformation layer in a 7050 aluminum alloy. With the combination of transmission electron microscopy (TEM) and high angle angular dark field scanning TEM (HAADF-STEM) observations, a surface ultrafine grain (UFG) layer composed of both equiaxed and lamellar ultrafine grains and decorated by high density of coarse grain boundary precipitates (GBPs) were revealed. Further precession electron diffraction (PED) assisted orientation mapping unraveled that high angle grain boundaries rather than low angle grain boundaries are the most favorable nucleation sites for GBPs. The prominent precipitate redistribution can be divided into three successive and interrelated stages, i.e. the mechanically induced precipitate dissolution, solute diffusion and reprecipitation. The quantitative prediction based on pipe diffusion along dislocations and grain boundary diffusion proved the distribution feasibility of GBPs around UFGs. Based on PED and electron backscatter diffraction (EBSD) analyses, the crystallographic texture of the surface UFG layer was identified as a shear texture composed of major rotated cube texture {001} 〈110〉 and minor {111} 〈112〉, while that of the adjoining lamellar coarse grained matrix was pure brass. The SFT induced surface severe shear deformation is responsible for texture evolution.
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TL;DR: In this paper, the dissolution of an ultra-high strength Al-Zn-Mg-Cu alloy was studied by SEM, TEM, DSC, hardness and electrical conductivity test and the dissolution process gradually reached into a balance with more than 95% had been eliminated and prolonging time imposes no evident influence on promoting the dissolution.
Abstract: Homogenization treatment of an ultra-high strength Al-Zn-Mg-Cu alloy was studied by SEM, TEM, DSC, hardness and electrical conductivity test. The second phases in as-cast 7A56 alloy are AlZnMgCu, Al 2 Cu and Al 7 Cu 2 Fe. AlZnMgCu phase has a similar lattice structure of MgZn 2 . After 380 °C homogenization treatment, transformation from AlZnMgCu to Al 2 CuMg occurred; after 470 °C homogenization treatment, AlZnMgCu were mainly directly dissolved into the matrix with no Al 2 CuMg discovered. That phenomenon was caused by the diffusion behavior of Zn and Cu at two different temperatures that Zn diffuses rapidly even at 380 °C while Cu shares a much lower diffusion rate. Much of the AlZnMgCu phase can be dissolved at 470 °C for a short time while at 380 °C it was seldom eliminated. After homogenized at 470 °C for 24 h, the dissolution process gradually reached into a balance with more than 95% had been eliminated and prolonging time imposes no evident influence on promoting the dissolution. Hardness and electrical conductivity are highly consistent with the vibration of AlZnMgCu phase, with the dissolution of which the hardness increases while electrical conductivity decreases.
60 citations
TL;DR: The microstructural evolution, texture and mechanical properties of nine Mg-4Zn-xCa-yMn alloys (x = 0.3, 0.6, 1.0; y= 0.2 and 0.7, respectively) were investigated systematically as mentioned in this paper.
Abstract: The microstructural evolution, texture and mechanical properties of nine Mg-4Zn-xCa-yMn alloys (x = 0.3, 0.6, 1.0; y = 0.2, 0.3, 0.7 wt.%) were investigated systematically. Alloying with Ca and Mn refined the grains of the extruded sheets and increased the unDRX fraction. Mn could be the heterogeneous nucleation site of Ca2Mg6Zn3 phase because of a good atom matching at the orientation relationship of ( 2 ¯ 1 ¯ 1 ¯ ) Mn//(1 2 ¯ 11)Ca2Mg6Zn3, 〈 2 ¯ 5 1 ¯ 〉 Mn//〈1103〉Ca2Mg6Zn3. The traditional texture weakening effect of Ca was strongly decreased for the simultaneously addition of Mn. With increasing Ca and Mn concentration, the strength increased and ductility decreased. Mg-4Zn-0.6Ca-0.7Mn exhibited a good combination of ultimate tensile strength (320 MPa), yield strength (286 MPa) and elongation (16%). A model of strengthening indicated that grain boundary strengthening and precipitate strengthening made a large contribution to the strength of Mg-4Zn-0.6Ca-0.7Mn. In addition, the dynamic recrystallization, texture modification and the strengthening effect from different parts also have been analyzed in detail.
47 citations
TL;DR: The precipitate and solute distribution in a surface severely plastically deformed Al-Cu-Mg alloy were revealed by means of transmission electron microscopy and atom probe tomography as mentioned in this paper.
Abstract: The precipitate and solute distribution in a surface severely plastically deformed Al-Cu-Mg alloy were revealed by means of transmission electron microscopy and atom probe tomography. Accompanying gradient grain structure, there is a gradient precipitate architecture which evolves from undeformed needle-like S (Al2CuMg) precipitates to shear-deformed and fragmented S precipitates along low angle dislocation boundaries within coarse grains, to reprecipitated Gunier-Preston-Bagaryatsky (GPB) zones and S precipitates in lamellar nanograins, and to completely dissolved and segregated solutes to nanograin boundaries. Dislocation activities induced precipitate dissolution and promoted solute diffusion are two concomitant processes during precipitate and solute redistribution. The variation of precipitate crystallography, including orientation relationship deviation and coherency loss between S precipitates and Al matrix, was attributed to local changes in strain fields around undissolved S precipitates and in nucleation environment for reprecipitated S phase.
32 citations
TL;DR: In this article, asymmetric feeder die extrusion was introduced on high strength Al-Zn-Mg alloy, and the results showed that the utilization of feeder chamber results in the increase of effective strain and slight decrease of strain rate.
Abstract: The asymmetric feeder die extrusion was introduced on high strength Al-Zn-Mg alloy. The hot extrusion experiments were carried out using flat die without feeder, with symmetric and asymmetric feeders. The grain morphology, second particle distribution and microtexture were examined, and the tensile tests were performed along 0°, 45°, and 90° with extrusion direction. Moreover, the numerical simulation was performed to have a better understanding on the experimental findings. The results show that the utilization of feeder chamber results in the increase of effective strain and slight decrease of strain rate. The microstructure of all extruded plates consists of elongated grains and small amount of fine grains. The asymmetry feeder is favorable for the dynamic recovery process. Although the fraction of dynamic recrystallization is low in all cases, it is slightly higher in the plate extruded without feeder. The main texture components of the extruded plates are {110}〈111〉 Y, {001}〈100〉 Cube, and {110}〈112〉 Brass. The fraction of above mentioned texture varies significantly by the utilization of symmetric and asymmetric feeders. The elongation is greatly enhanced in the plates extruded by feeder die. Importantly, the anisotropy of elongation is obviously reduced in the plate extruded using the asymmetric feeder.
25 citations
TL;DR: In this paper , a remarkable annealing hardening effect was detected in gradient ultrafine-grained (UFG) Mg-0.32Gd- 0.11Zr alloy sheet fabricated by sliding friction treatment (SFT).
Abstract: In this study, a remarkable annealing hardening effect was detected in gradient ultrafine-grained (UFG) Mg-0.32Gd-0.11Zr (at.%) alloy sheet fabricated by sliding friction treatment (SFT). Under the precipitation-free condition, the annealed UFG structure shows an obvious hardness increment from 1.40 GPa to 1.89 GPa after 200°C heating for 12 h, which exhibits a much higher hardening response than the annealed coarse-grained (CG) structure. The high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and elemental mapping reveal prominent segregation of solute Gd atoms along grain boundaries, which endows the UFG structure with excellent grain boundary stability. Moreover, Gd segregation is also found around the extrinsic stacking fault (E-SFs) and the low-angle grain boundaries composed of edge dislocations. The large-scale solute partitioning provides a significant segregation hardening effect, which completely resists the softening effect aroused by the grain coarsening and dislocation annihilation. This work realizes a good combination of surface mechanical processing for fabricating UFGs and subsequent heat treatment, which earns desirable segregation hardening effects.
20 citations
References
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01 Jan 1981TL;DR: In this article, the authors discuss the properties of phase diagrams for single-component systems, including the influence of interfaces on the equilibrium of binary solutions in Heterogeneous Systems (Heterogeneous Binary Phase Diagrams).
Abstract: Thermodynamics and Phase Diagrams Equilibrium Single-Component Systems Binary Solutions Equilibrium in Heterogeneous Systems Binary Phase Diagrams Influence of Interfaces on Equilibrium Ternary Equilibrium Additional Thermodynamic Relationships for Binary Solutions Computation of Phase Diagrams Kinetics of Phase Transformations Exercises References Further Readings Diffusion Atomic Mechanisms of Diffusion Interstitial Diffusion Substitutional Diffusion Atomic Mobility Tracer Diffusion in Binary Alloys Diffusion in Ternary Alloys High-Diffusivity Paths Diffusion in Multiphase Binary Systems Exercises References Further Readings Crystal Interfaces and Microstructure Interfacial Free Energy Solid=Vapor Interfaces Boundaries in Single-Phase Solids Interphase Interfaces in Solids Interface Migration Exercises References Further Readings Solidification Nucleation in Pure Metals Growth of a Pure Solid Alloy Solidification Solidification of Ingots and Castings Solidification of Fusion Welds Solidification during Quenching from the Melt Metallic Glasses Case Studies of Some Practical Castings and Welds Exercises References Further Readings Diffusional Transformations in Solids Homogeneous Nucleation in Solids Heterogeneous Nucleation Precipitate Growth5 Overall Transformation Kinetics-TTT Diagrams Precipitation in Age-Hardening Alloys Precipitation of Ferrite from Austenite Cellular Precipitation Eutectoid Transformations Massive Transformations Ordering Transformations Case Studies Exercises References Further Readings Diffusionless Transformations Characteristics of Diffusionless Transformations Martensite Crystallography Theories of Martensite Nucleation Martensite Growth1 Premartensite Phenomena Tempering of Ferrous Martensites Case Studies Exercises References Further Readings Solutions to Exercises Compiled by John C. Ion
4,104 citations
TL;DR: The focus of this paper is aircraft and aircraft engines but the broader focus is on the role of materials in creating lightweight structures, and there are examples used that are relevant to automotive applications once they are adjusted for cost.
Abstract: This paper examines the progress in aircraft and aircraft engines from the standpoint of the role that better materials and processing has played. Such progress includes the relatively recent transformation of the aircraft industry from purely performance driven products to products that are driven by customer value. It is demonstrated that advances in materials and processing technology and understanding has enabled much of the progress that has been made since the inception of manned, heavier than air flight. The recent constraints of cost, as determined by customer value, have changed the way new materials are introduced and these trends appear to be the new paradigm for the aircraft and aircraft engine industry. While the focus of this paper is aircraft and aircraft engines, the broader focus is on the role of materials in creating lightweight structures. There are examples used in this paper that are relevant to automotive applications once they are adjusted for cost. This matter is briefly discussed at the end of the paper.
1,746 citations
TL;DR: The extraordinary intrinsic plasticity of gradient NG structures offers their potential for use as advanced coatings of bulk materials in both high strength and ductility materials.
Abstract: Nano-grained (NG) metals are believed to be strong but intrinsically brittle: Free-standing NG metals usually exhibit a tensile uniform elongation of a few percent. When a NG copper film is confined by a coarse-grained (CG) copper substrate with a gradient grain-size transition, tensile plasticity can be achieved in the NG film where strain localization is suppressed. The gradient NG film exhibits a 10 times higher yield strength and a tensile plasticity comparable to that of the CG substrate and can sustain a tensile true strain exceeding 100% without cracking. A mechanically driven grain boundary migration process with a substantial concomitant grain growth dominates plastic deformation of the gradient NG structure. The extraordinary intrinsic plasticity of gradient NG structures offers their potential for use as advanced coatings of bulk materials.
1,198 citations
TL;DR: A grain refinement mechanism induced by plastic deformation during the SMA treatment in Fe was proposed in this article, which involves formation of dense dislocation walls (DDWs) and dislocation tangles (DTs) in original grains and in the refined cells under further straining.
Abstract: By means of surface mechanical attrition (SMA), a nanostructured surface layer was formed on a pure Fe plate. Microstructure features of various sections in the surface layer, from the strain-free matrix to the treated top surface, were systematically characterized by using X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. Based on the experimental observations, a grain refinement mechanism induced by plastic deformation during the SMA treatment in Fe was proposed. It involves formation of dense dislocation walls (DDWs) and dislocation tangles (DTs) in original grains and in the refined cells (under further straining) as well, transformation of DDWs and DTs into subboundaries with small misorientations separating individual cells or subgrains, and evolution of subboundaries to highly misoriented grain boundaries. Experimental evidences and analysis of the grain refinement mechanism indicate that high strains with a high strain rate are necessary for formation of nanocrystallites during plastic deformation of metals. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
889 citations
TL;DR: Gradient microstructures, in which the grain size increases from nanoscale at the surface to coarse-grained in the core, were recently discovered to be an effective approach to improving ductility.
Abstract: Steels can be made stronger, tougher, or more resistant to corrosion either by changing composition (adding in more carbon or other elements) or by modifying their microstructures. An extreme microstructural route for strengthening materials is to reduce the crystallite size from the micrometer scale (“coarse-grained”) to the nanoscale. Nanograined aluminum or copper (Cu) may become even harder than high-strength steels, but these materials can be very brittle and crack when pulled (deformed in tension), apparently because strain becomes localized and resists deformation. However, nanograined metals can be plastically deformed under compression or rolling at ambient temperature, implying that moderate deformation can occur if the cracking process is suppressed. Tremendous efforts have been made to explore how to suppress strain localization in tensioned nanomaterials and make them ductile. Gradient microstructures, in which the grain size increases from nanoscale at the surface to coarse-grained in the core, were recently discovered to be an effective approach to improving ductility ( 1 – 4 ).
755 citations