Commercially pure aluminium was subjected to friction stir processing (FSP) to study the microstructure developed and its effects on the mechanical properties. Friction stir processing refined the grain size to 3. μm in a single pass from the starting coarse grain size of 84. μm. Electron backscattered diffraction (EBSD) results showed occurrence of dynamic recrystallization and also revealed existence of different orientations within the stir zone and across the transition zone. Transmission electron microscopy (TEM) revealed fine grains with well defined boundaries. The arrangement and absorption of dislocation into the sub-grain boundaries, formed by dynamic recovery, was also revealed by TEM. The yield strength of the material was improved by a factor of 2.4 after FSP owing to grain refinement. The most important feature of the friction stir processed material was that even after this significant improvement in strength there was little loss of ductility. The hardness also improved by 34% with the peak hardness being observed towards the advancing side. © 2012 Elsevier B.V.

Ranjit Bauri

Department of Metallurgical and Materials Engineering

Advancing side

COARSE GRAIN SIZE

Dynamic recovery

EBSD

Electron back-scattered diffraction

Fine grains

Friction stir

Friction stir processing

grain size

Mechanical characterizations

Microstructure and mechanical properties

Peak hardness

PURE ALUMINIUM

SINGLE PASS

STIR ZONES

SUBGRAIN BOUNDARIES

Thermo-mechanical processing

TRANSITION ZONES

Aluminum

Dynamic recrystallization

Grain boundaries

Grain refinement

Grain size and shape

Hardness

microstructure

Strength of materials

Transmission electron microscopy

Aluminum alloys

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IIT Madras

Materials Science and Engineering A

The present study demonstrates that friction stir processing (FSP) can be used as a mechanical alloying tool to process solid solution. Zn was incorporated in commercially pure aluminium by multi-pass FSP leading to its dissolution and formation of supersaturated solid solution which was confirmed by X-ray diffraction and scanning electron microscopy. The hardness across the stir zone matched with the distribution of Zn and was significantly improved compared to the base metal. The supersaturated solid solution that formed in the first pass, partially decomposed during the second pass, leading to the formation of fine Al-Zn precipitates. Thermal stability of the microstructure against abnormal grain growth was also improved after the second pass due to the pinning effect of the grain boundary precipitates. FSP also caused grain refinement of the alloy yielding fine equiaxed grains in the range of 4–6 μm with a high fraction (> 67%) of high angle grain boundaries. Such microstructure is conducive for isotropic properties and the fact that the microstructure is stable against thermal cycles make the process suitable for selective alloying for location specific property enhancement. © 2017 Elsevier Inc.

Materials Characterization

Fabrication of Al-Zn solid solution via friction stir processing

In this study, dense fine-grained ZrB2 and TiB2 were fabricated using reactive spark plasma sintering (RSPS) of ball-milled Zr/B and Ti/B mixtures. Systematic investigations were carried out to understand the mechanisms of reactive sintering. Two densification mechanisms were found to be operating during RSPS. The first stage of densification was due to self-propagating high temperature synthesis reaction leading to formation of ZrB2 and TiB2 compacts having relative density of ~48 and ~65%, respectively. The second stage of densification occurred at temperatures more than 1100 °C and resulted in final relative density of more than 98%. Electron backscatter diffraction and electron microscopy studies on interrupted RSPS samples as well as dense samples showed deformed grains and presence of slip steps while grain orientation spread map and pole figure analysis confirmed plastic flow. Plastic flow-aided pore closure is shown as major mechanism during reactive sintering. © 2017 Informa UK Limited, trading as Taylor & Francis Group.

Philosophical Magazine

Densification mechanisms during reactive spark plasma sintering of Titanium diboride and Zirconium diboride

Aluminum-based in situ composites suffer from the age-old issue of particle segregation along the grain boundaries after casting. In the present study, friction stir processing (FSP) was employed as a secondary process to improve the distribution of in situ formed TiB2 particles in Al-based composite. All the agglomerates of TiB2 were broken, and uniform distribution of particles was achieved after double-pass FSP. Also, FSP removed the casting defects and caused significant grain refinement of the Al matrix. The microstructure was characterized by equiaxed fine grains with average size of 3 µm and narrow grain size distribution. The microstructural refinements and homogenization after FSP not only enhanced the strength but also improved the ductility of the as-cast composite. © 2015, ASM International.

Journal of Materials Engineering and Performance

Friction Stir Processing of Al-TiB2 In Situ Composite: Effect on Particle Distribution, Microstructure and Properties

In the present study Ni particles were incorporated in 5083 Al alloy by friction stir processing (FSP) to fabricate metal particle reinforced composite. A conventional cylindrical tool was first used for FSP and several processing parameters (rotational and traverse speeds) were exploredto get a defect free stir zone and uniform distribution of the particles. The effect of tool geometry was also studied by using another tool having special features on the pin and the shoulder. A tool rotation speed of 1200. rpm and traverse speed of 0.4. mm/s were found to be optimum for obtaining a defect free stir zone. However, the distribution of Ni particles was inhomogeneous for all the parameters used with the plain cylindrical tool irrespective of defective or a sound stir zone. The tool with the special features, threads on the pin and spiral grooves on the shoulder, was found to be very effective in both producing a sound stir zone and dispersing the Ni particles. It was also found that ball milled fine particles were dispersed more uniformly in the stir zone compared to the as-received coarse particles. FSP also refined the grain size of the aluminium matrix from 25μm to 3μm. The microstructure was characterised by equiaxed fine grains with a high fraction of high angle grain boundaries and a narrow grain size distribution. The effect of the particle incorporation on the mechanical properties of the alloy was also investigated. The strength increased significantly compared to the base alloy and more importantly a high amount of ductility was also achieved in the composite. © 2015 Elsevier Ltd.

Materials Today: Proceedings

Effect of Process Parameters and Tool Geometry on Fabrication of Ni Particles Reinforced 5083 Al Composite by Friction Stir Processing

Single pass and double-pass friction stir processing was carried out on commercially pure aluminium and a detailed electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) analysis was carried out to understand the effect of the second pass on the microstructure developed. The grain size was refined substantially after the first pass due to occurrence of dynamic recrystallization process as revealed by EBSD analysis. TEM observations revealed dislocation structures inside the grains. There was no significant change in the grain size and the other microstructural features were similar except that the free dislocations observed inside grains after the first pass were well arranged into subgrain boundaries after the second pass. This indicates that the final grain size after friction stir processing does not depend on the starting grain structure. EBSD also revealed some variation in microstructural features such as grain size, % of HABs, texture index, grain orientation spread across the surface and also in the cross section of the stir zone both after single and double pass. © (2013) Trans Tech Publications, Switzerland.

Materials Science Forum

Microstructure development in single and double-pass friction stir processing of aluminium

Nickel particles were embedded into an Al matrix by friction stir processing (FSP) to produce metal particle reinforced composite. FSP resulted in uniform dispersion of nickel particles with excellent interfacial bonding with the Al matrix and also lead to significant grain refinement of the matrix. The novelty of the process is that the composite was processed in one step without any pretreatment being given to the constituents and no harmful intermetallic formed. The novel feature of the composite is that it shows a three fold increase in the yield strength while appreciable amount of ductility is retained. The hardness also improved significantly. The fracture surface showed a ductile failure mode and also revealed the superior bonding between the particles and the matrix. Electron backscattered diffraction (EBSD) and transmission electron microscopy analysis revealed a dynamically recrystallized equiaxed microstructure. A gradual increase in misorientation from sub-grain to high-angle boundaries is observed from EBSD analysis pointing towards a continuous type dynamic recrystallization mechanism. © 2010 Elsevier B.V.

Processing, microstructure and mechanical properties of nickel particles embedded aluminium matrix composite

Friction stir processing was carried out on commercially pure aluminium, and a detailed microstructural characterisation was performed by electron backscattered diffraction and transmission electron microscopy. Friction stir processing resulted in significant grain refinement with narrow grain size distribution. The microstructure showed fine and equiaxed grains, with some ultrafine grains being also observed. Electron backscattered diffraction studies showed majority of the boundaries to be high angle, confirming the occurrence of dynamic recrystallisation (DRX). Transmission electron microscopy observations revealed dislocation arrangement into subgrain boundaries, grains having different dislocation densities and in different stages/degrees of recovery. Electron backscattered diffraction analysis also revealed a progressive transformation of sub-grain boundaries into high angle grain boundaries. A multimechanism of dynamic recovery, continuous DRX and discontinuous DRX seems to be operating during the process. The microstructure is not affected by changing the rotation speed from 640 to 800 rev min -1, except that the grain size was marginally larger for higher rotational speed. © 2011 Institute of Materials, Minerals and Mining.

Materials Science and Technology

Microstructural characterisation of friction stir processed aluminium

Friction Stir Welding and Processing VIII

Materials Science and Engineering: A

High tensile ductility via enhanced strain hardening in ultrafine-grained Cu

Mechanical properties and microstructure evolution of 1050 aluminum severely deformed by ECAP to 16 passes

Effect of friction stir processing on microstructure and mechanical properties of aluminium

Journal	Materials Science and Engineering A
ISSN	09215093
Open Access	No