Grain Growth Behavior and Hall–Petch Strengthening in Friction Stir Processed Al 5059

Friction stir processing (FSP) of Al 5059 is studied in which subsequent heat treatment is conducted to investigate its effects on grain size and hardness. It was found that mainly elongated and rhomboidal morphologies of Al₆(Mn,Fe) particles are present in the alloy both before and after FSP, where the rhomboidal particles are more effective in pinning grain boundaries during heat treatment. The stir zone reached a temperature of 705 K (432 °C), and ThermoCalc modeling confirmed that the Al₆(Mn,Fe) particles will remain stable at this temperature. Negligible grain growth was observed during FSP of the Al 5059 due to low grain boundary mobility resulting from slow diffusion associated with a high Mg content in the alloy. During heat treatment at 448 K (175 °C) grain growth could be correlated with time using a particle-controlled grain growth model. Microhardness values indicate that Hall–Petch behavior occurs in the processed alloy, while dislocation density and particle dispersion play a minor role in strengthening.     

Microhardness and Texture Evolution of Ultralight Mg–Li Alloy Processed by Cold Rolling

Russian Journal of Non-Ferrous Metals - Single β-type Mg–12Li and Mg–12Li–1Al (wt %) alloy sheets were prepared by casting, followed by cold rolling. Microstructure and...     

Effects of Route on Microstructural Evolution and Mechanical Properties of Cu-8 Wt Pct Ag Alloy Processed by Equal Channel Angular Pressing

Equal channel angular pressing (ECAP) is applied to investigate the microstructural evolution and mechanical properties of Cu-8 wt pct Ag alloy subjected to one to four passes via four different routes (A, B_A, B_C, and C). It is demonstrated that better mechanical properties, a higher fraction of high-angle boundaries, and a smaller grain size can be obtained most rapidly with route A, whereas the specimen processed by route B_C contains relatively inhomogeneous microstructure and has poor mechanical properties. The ultimate tensile stress (UTS) of the Cu-Ag alloy processed by route B_C saturates after four passes; in contrast, the UTS of the Cu-Ag alloy processed by route A increases continuously in relation to the number of ECAP passes. Based on the experimental results, the strengthening mechanisms of the Cu-8 wt pct Ag alloy processed by different routes as well as the efficiency of different routes in refining the binary alloy are discussed.     

The Friction Stress of the Hall–Petch Relationship of Pure Mg and Solid Solutions of Al,Zn, and Gd

Temperature and solute concentration effects on the friction stress, σ_o, of cast (texture-free) polycrystals of pure Mg, and of Mg-Al, -Zn and -Gd binary solid solutions are discussed using phenomenological arguments. The temperature effects on the pure metal suggest that σ_o relates to the ratio between the CRSS of prism and basal slip, against early suggestions that it should only relate to the CRSS for basal slip. Solid solution softening upon prism slip accounts for the minima in σ_o at ~ 0.5 at. pct in Mg-Zn and Mg-Gd alloys. In the concentrated alloys, solute-specific hardening effects upon slip and twinning lead to diverging behaviors: in Mg-Al and Mg-Zn, σ_o remains below that of pure Mg. Strong short-range order by Gd leads to a steep monotonic increase, and to a value larger in compression than in tension due to the activation of {10-11} twinning at high concentrations. The negative σ_o of the dilute Mg-Zn alloys is an artifact created by the tension/compression asymmetry stemming from the polar character of {10-12} twinning.     

Evolution of Texture,Strain, and Grain Boundary Constitution in Copper–Chromium Coatings and its Effect on Coating Corrosion Behavior

Metallurgical and Materials Transactions A - Microstructural alterations in electrodeposited Cu–Cr coatings (1.5, 3.6, and 6.5 wt pct Cr) and their impact on the coating corrosion behavior...     

Finite Element Analysis of Die Geometry and Process Conditions Effects on Equal Channel Angular Extrusion for β-Titanium Alloy

 The finite element analysis was applied to evaluate the respective influences of die geometry and process conditions on plastic strain distribution for β-titanium (Ti-13V11Cr3Al) alloy during the equal channel angular extrusion (ECAE). It was found that optimum equal channel angular extrusion die geometry is strongly material dependent. Optimal strain homogeneity in the Ti-13V11Cr3Al alloy may be achieved at r (inner radius)=5 mm, R (outer radius)=3 mm. The equivalent plastic strain increases with increasing friction coefficient. And the better homogeneity of the equivalent plastic strain distribution can be achieved when friction coefficient value is lower. The faster the ram speed is, the lower the homogeneity of the equivalent plastic strain distribution is and the influence is slight. The back-pressure does not help to improve the plastic strain homogeneity, and the increasing temperature has a slightly favourable effect on the plastic strain homogeneity between 400 and 600 ℃.     

Effect of Deposition Temperature on the Evolution of Texture,Grain Boundary Constitution and Corrosion Behaviour of Sn–Cr Coatings

Metallurgical and Materials Transactions A - Effect of deposition temperature on the evolution of microstructure and corrosion properties of electrodeposited SnCr coatings was studied. The coatings...     

Dependence of the Grain Size in the Microstructure of Copper on the Rate of Deformation by “Helical Rolling–Pressing”

Metallurgist - The authors consider the refinement of the microstructure of copper (grade M1) on the rate of deformation using a “helical rolling-pressing” method. The deformation was...     

Correlation Between Texture,Grain Boundary Constitution and Corrosion Behaviour of Copper–Chromium Coatings Containing Graphene Oxide

Metallurgical and Materials Transactions A - Effect of graphene oxide on the corrosion behavior of electrodeposited Cu–Cr coatings on mild steel substrate was studied and the results were...     

Effect of Recovery and Recrystallization on the Hall–Petch Relation Parameters in Submicrocrystalline Metals: II. Model for Calculating the Hall–Petch Relation Parameters

A model is developed to calculate the Hall–Petch relation parameters for the submicrocrystalline (SMC) metals fabricated by severe plastic deformation (SPD) methods. The model is based on the assumption that the flow stress in SMC metals includes both conventional contributions (caused by lattice dislocations, impurity atoms, etc.) and a contribution related to the long-range internal stress fields created by the SPD-induced defects distributed over grain boundaries. Equations are derived to calculate the Hall–Petch relation parameters as functions of the strain and the strain rate. The results calculated by the derived equations agree well with the experimental data. The low resistance of grain boundaries to the motion of grain boundaries in SMC materials (see part I of this work) is found to be related to a violation of the Hall–Petch relation in SMC metals.     

Impact of Volume Fraction and Size of Reinforcement Particles on the Grain Size in Metal–Matrix Micro and Nanocomposites

In metal–matrix micro and nanocomposites (MMCs and MMNCs), the presence and interactions of various strengthening mechanisms are not well understood, but grain boundary strengthening is considered as one of the primary means of improving the yield strength of composites. Owing to the importance of grain size on mechanical properties, it is necessary to be able to describe how incorporation of nanoparticles (NPs) in both powder metallurgy (PM) and solidification processing (SP) affects this critical property. In the present work, we provide a basis for an empirical equation that relates particle fraction and particle size to MMNC grain size for both PM and SP synthesis methods. The model suggests that NPs retard grain coarsening in PM MMNCs and also seems to describe the effect of reinforcement concentration on grain size in SP MMCs and MMNCs.     

Evolution of Texture,Grain Boundary Constitution,Strain, and Corrosion Behavior of Electrodeposited Ni–P Coatings as a Function of Deposition Current Density

Metallurgical and Materials Transactions A - Ni–P coatings with low P content (P wt pct < 1.0) were fabricated at different applied current densities of electrodeposition...     

Structure and Mechanical Properties of Al–Ca–Mn–Fe–Zr–Sc Eutectic Aluminum Alloy after Warm Equal Channel Angular Pressing

Russian Journal of Non-Ferrous Metals - Recently developed multicomponent eutectic alloys based on Al–Ca are promising for practical application, since they are characterized by low density...     

The Effect of Bridge Geometry on Microstructure and Texture Evolution During Porthole Die Extrusion of an Al–Mg–Si–Mn–Cr Alloy

Porthole die extrusion is used to produce complex hollow aluminum cross-sections for automotive applications. In a porthole die, the material is first divided into multiple streams which are separated by a bridge, before rejoining in the weld chamber and finally passing through the die orifice. The rejoining of the material in the weld chamber produces lines known as weld lines in the final extruded product. The microstructure along the weld line and its associated quality are strongly influenced by the thermal-mechanical history the material experiences as it passes through the portholes, the weld chamber, and the die orifice, which can be altered by die design and, in particular, the bridge geometry. To study the influence of bridge geometry on weld line microstructure and final quality, a series of porthole die extrusion experiments was conducted using an Al–Mg–Si–Mn–Cr alloy and two different types of bridge geometry (streamlined and flat). The experimental results showed that bridge geometry had a significant effect on the local microstructure and crystallographic texture at the weld line. Specifically, EBSD analysis indicated that the weld line texture associated with a streamlined bridge geometry consisted of a deformation texture (mainly the copper component), while the local texture produced by a flat bridge was a recrystallization texture consisting of Cube, Goss, and Cube_RD texture components. Simulation of the extrusion process, using DEFORM 3D, indicated that the weld line produced using a flat bridge experienced a slightly higher temperature, but much higher equivalent strains than the streamlined case. Material away from the weld line was very similar for both cases, indicating that the effect of the die bridge geometry is localized to the region close to the weld line.

     

The Influence of Equal Channel Angular Pressing on Structure and Mechanical Properties of New β-Ti Alloy Ti–10Mo–8Nb–6Zr

Russian Journal of Non-Ferrous Metals - This work presents comparative studies of structural and mechanical properties of a new β-Ti alloy Ti–10Mo–8Nb–6Zr exposed to...     

Effect of Recovery and Recrystallization on the Hall–Petch Relation Parameters in Submicrocrystalline Metals: I. Experimental Studies

Yield strength σy, macroelastic limit σ₀, and effective grain-boundary hardening coefficient K_eff in the Hall–Petch relation (\({\sigma _y} = {\sigma _0} + {K_{eff}}/\sqrt d \)) in the submicrocrystalline (SMC) materials produced by equalchannel angular pressing are experimentally studied. It is shown that, as compared to parameter σ₀ and K in the Hall–Petch relation for coarse-grained metals, the SMC metals are characterized by higher values of σ0 and lower values of K_eff. The critical grain size (d₁) at which Keff in the σ_y–d^–1/2 relations of SMC materials changes falls in the range 0.2–0.5 μm. The dependences of macroelastic limit σ₀ and coefficient K_eff on the annealing temperature are found to be determined by recrystallization. If abnormal grain growth develops in annealing of SMC metals, anomalous hardening is detected and a nonmonotonic temperature dependence of coefficient K_eff takes place. In the case of conventional recrystallization at a high annealing temperature, SMC metals exhibit a smooth decrease in σ₀ and an increase in K_eff to the values of K characteristic of coarsegrained materials.     

Amorphous Intergranular Film Effect on the Texture and Structural Evolution During Cold-Rolling of Nanocrystalline Ni–Zr Alloys

Metallurgical and Materials Transactions A - The presence of amorphous intergranular films (AIFs) in nanocrystalline (NC) metals improves the mechanical properties and thermal stability. However,...     

Investigation into the Formation of Texture,Microstructure, and Anisotropy of Properties during Rolling Sheets of the Aluminum–Lithium 1420 Alloy

Results of investigations into the formation of the crystallographic orientation of the structure and anisotropy of properties during rolling sheets of the aluminum–lithium 1420 alloy of the Al–Mg–Li system are given. Hot-rolled billets of the 1420 alloy were cold-rolled with intermediate quenching according to the following schedule: 7.3 mm → 4.8 mm → 3.0 mm → 1.8 mm. The samples were selected after each passage to perform mechanical testing and analyze the structure using optical microscopy and diffractometry. A deformed fibrous structure and considerable anisotropy of mechanical properties is characteristic of sheets of all considered states. Herewith, the maximal plasticity is observed at an angle of 45° to the rolling direction. The character of anisotropy of properties formed at the hot-rolling stage is not varied during cold rolling. Sheets of the 1420 alloy have a sharp deformation texture at all rolling stages due to the conservation of the unrecrystallized structure. For example, when analyzing pole figures and preferential orientations, an increase in volume fractions of rolling texture is revealed (the slow one of the brass type and more rapid of the S type) with the rise of summary deformations of cold rolling. The recrystallization texture (of the R type) is present in small amounts only after hot rolling. The volume fraction of the texture-free component decreases with an increase in summary deformations. It is concluded based on these results that, in order to decrease the fraction of the deformation texture and lower anisotropy of properties in sheets of the 1420 alloy, it is first and foremost necessary to provide the running of recrystallization at the hot-rolling stage in order to fabricate the recrystallized hot-rolled billet for subsequent cold rolling.     

Efficient Recovery of Copper and Cobalt from the Matte–Slag Mixture of ISA Furnace by Injection of Coke and Pyrite

During ISA copper smelting process, ISASMELT furnace discharges a large amount of matte and slag mixture and the separation of them has an important influence on the recovery of valuable metals. This paper presented a reduction-sulfurization sedimentation process for recovering copper and cobalt from the matte–slag mixture of ISA furnace. Firstly, matte–slag mixture and traditional static sedimentation slag are characterized to determine their mineral composition and occurrence state. It indicates that Cu is primarily lost in slag in the form of sulfide, while Co is mostly lost in the form of oxide. With coke and pyrite as the reducing agent and vulcanizing agent, an orthogonal laboratory experiment was conducted to determine the effects of the smelting temperature and additive dosage on the recovery process. The optimum slag cleaning conditions were found to be: a coke dosage of 2 pct, a pyrite dosage of 2 pct, and a smelting temperature of 1260 °C lasting for 2 hours. In order to improve on the low utilization ratio of additives associated with the industrial sedimentation process, an innovative additive introducing method was put forward which enables the additives to mix and react with slag more adequately. A powder injection device was purpose-made to inject additives into molten slag in dispersion state, and a laboratory experiment was carried out to simulate this process. By injecting 2 pct coke and 2 pct pyrite, the contents of Cu and Co in cleaned slag decreased to 0.46 and 0.01 pct, respectively. It proves that the injection of additives into molten slag is an effective method to recover Cu and Co from the matte–slag mixture of ISA furnace.     

Effect of Starting As-cast Structure on the Microstructure–Texture Evolution During Subsequent Processing and Finally Ridging Behavior of Ferritic Stainless Steel

Metallurgical and Materials Transactions A - Effect of the initial as-cast structure on the microstructure–texture evolution during thermomechanical processing of 409L grade ferritic...