Search

Expanding suitable severe plastic deformation processes seems essential to design lightweight wire-formed materials for emerging demands. In this regard, 6063 aluminum alloy in the form of wire was processed successfully by polyurethane rubber assisted-equal channel angular pressing up to 16 passes by route BC. It was found that significant improvement of hardness and strength is achieved at the initial passes due to the increment of material’s dislocations density which leads to the crystallite size decrease and lattice microstrain increase. Also, subsequent passes improve the mechanical properties with a gentle rate due to the saturation of dislocation strengthening. The fractography analysis indicated that the ductile fracture mode of the annealed aluminum decreases by imposing the ECAP process. It is related to the formation of cleavage and rive patterns and the reduction in the number and size of the dimples compared to the initial condition. Eventually, X-ray diffraction findings showed that by adding pass numbers, the isotropy degree of the aluminum sample enhances because of the lowest diffraction scattering.

Background The severe plastic deformation approach and its well-known cyclic extrusion compression (CEC) method have been established as a powerful tool for fabricating bulk ultrafine-grained metals and alloys with improved properties. Objective This study focused on the microstructure evolution, hardness behavior, and corrosion properties of the CEC-processed Al5052 up to four passes compared to the initial annealed state. Methods The initial and CEC-processed Al5052 samples at different pass numbers were examined experimentally by EBSD analyses, hardness measurements, and corrosion resistance. Results Substantial grain refinement was attained from ~23 μm for the annealed sample to ~0.8 μm in the four passes sample. In addition, the hardness values considerably increased up to 75.7% after four passes from the initial value of 80 HV. In addition, the increment of pass numbers led to a more uniform dispersion of hardness values. Furthermore, the production of more stable protective oxide layers on the UFG structure of the CEC-processed sample led to the improvement in electrochemical response with a corrosion rate reduction from 1.49 to 1.02 mpy, respectively, in the annealed and final pass CEC-processed samples. In fact, the annealed sample manifested more large-sized and deeper pits than the CECed samples due to the increment of potential values and electrochemical attack of chlorine ions that finally deteriorates the corrosion performance. Conclusions CEC is an efficient method to improve the mechanical properties of materials due to substantial microstructural changes along with enhancement of electrochemical behavior because of the presence of small-sized and shallow pits.

Orientation relationships (ORs) can form during solidification by a variety of mechanisms that are often difficult to distinguish after solidification. Here we study three ORs formed by the nucleation of Al3Ti on TiB2, and by the pushing and engulfment of TiB2 by growing Al3Ti facets in hyperperitectic Al-rich melts. The nucleation OR is identified by growing a relatively large TiB2 crystal, solidifying multiple small Al3Ti crystals on one (0001) facet of TiB2, and measuring the resulting OR by electron backscatter diffraction (EBSD). Pushing and engulfment ORs are investigated by statistical analysis of EBSD measurements, density functional theory (DFT) calculations of interface energies, and imaging of cross-sections of TiB2 particles being pushed and engulfed by Al3Ti facets. It is shown that the lowest energy OR is formed by nucleation as well as by pushing/engulfment. The higher energy ORs, formed by pushing and engulfment, correspond to local interfacial energy minima and can be explained by rotation of TiB2 particles on Al3Ti facets during pushing.

The grain refining effect of Zirconium (Zr) is known, nevertheless the effect of Zr amount and its effect on solidification and wear behavior of modified Mg-Zn alloys has not been adequately studied. Mg-4Zn-(x)Zr alloys alloyed with the addition of 0.5 wt.% to 4 wt.% Zr element are melted and poured into two different casting molds and thermal analyzes were performed. Casting microstructure, solidification behavior, phase transformations, grain size, thermal analysis curves and wear properties were examined. The microstructure was modified by the addition of Zr and the grain size was reduced for both graphite and ceramic mold materials. Maximum tensile strength was obtained by adding 1% Zr (170 MPa) and 4Zr (105-110 HRB) using graphite mold, respectively. The maximum room temperature tensile strength was achieved on the Mg-4Zn-1Zr alloy the elongation was 4.9 percent and the tensile strength was 138 MPa. The max hot tensile value was achieved on the 2 wt% Zr added alloys. The wear rate of Mg-4Zn alloy decreased with increasing Zr element up to 2 wt% Zr. Addition of more than 2% by weight of Zr caused an increase in microporosity in the microstructure. Due to the microporosity caused by the Zr addition, the wear rate was slightly reduced.

The microstructure of Sn-Ag-Cu (SAC) solder joints plays an important role in the reliability of electronics, and interlaced twinning has been linked with improved performance. Here, we study the three-dimensional (3-D) shape of interlaced regions in Sn-3.0Ag-0.5Cu (SAC305) solder balls by combining serial sectioning with electron backscatter diffraction. In solder balls without large Ag3Sn plates, we show that the interlaced volume can be reasonably approximated as a hollow double cone with the common 〈100〉 twinning axis as the cone axis, and the 〈110〉 from all three twinned orientations making up the cone sides. This 3-D morphology can explain a range of partially interlaced morphologies in past work on 2-D cross-sections.

Dendritic microstructural evolution during the solidification of Mg-Zn alloys was investigated as a function of Zn concentration using in situ synchrotron X-ray tomography. We reveal that increasing Zn content from 25 wt% to 50 wt% causes a Dendrite Orientation Transition (DOT) from a six-fold snow-flake structure to a hyper-branched morphology and then back to a six-fold structure. This transition was attributed to changes in the anisotropy of the solid-liquid interfacial energy caused by the increase in Zn concentration. Further, doublon, triplon and quadruplon tip splitting mechanisms were shown to be active in the Mg-38 wt%Zn alloy, creating a hyper-branched structure. Using the synchrotron tomography datasets, we quantify, for the first time, the evolution of grain structures during the solidification of these alloys, including dendrite tip velocity in the mushy zone, solid fraction, and specific surface area. The results are also compared to existing models. The results demonstrate the complexity in dendritic pattern formation in hcp systems, providing critical input data for the microstructural models used for integrated computational materials engineering of Mg alloys.

The individual and combined effects of W and Zr additions on macrostructure, microstructure and mechanical properties of Nb have been investigated. Nb, Nb-10 wt% W, Nb-2.5 wt% Zr and Nb-10 wt% W-2.5 wt% Zr alloy ingots were prepared by electron beam drip melting using high purity Nb, W and Zr rods. Additions of W and Zr resulted in significant improvement in hardness and room temperature tensile strength. It is seen that the effect of 10 wt% W addition is more than that of 2.5 wt% Zr addition in improving room temperature strength of Nb, although on ‘per wt% addition’ basis, Zr is a more effective strengthener than W. It is also observed that the cumulative effects of 10 wt% W and 2.5 wt% Zr on grain refinement and strengthening are more than their respective individual effects.

Friction stir welding (FSW) since its invention has been attracting relevant interest for joining aluminium alloys. Due to the nature of this process, the materials can be joint without melting. Thanks to this peculiar characteristic, the issues associated with the cooling from liquid phase are avoided or considerably reduced, such as cracking, porosity, and defects. However, as well as other well-established welding techniques, the FSW process gives rise to formation of residual stress in the welding region and surrounding volume: heat and thermo-mechanical affected zones. Presence of residual stress in a mechanical component is well-known to affect its performance, particularly regarding fatigue at high number of cycles. Another aspect that influences the fatigue life is the underlying microstructure. In this work, we firstly study the residual stress field and the underlying microstructural features arising in FSW butt joints and their effect on the fatigue performance of this type of weldments. The evaluation of residual stress field is carried out by means of modern experimental techniques. In the first instance, synchrotron X-ray powder diffraction was employed for two-dimensional full field maps of residual stress. Corroboration of these measurements was done by exploiting the capability of focused ion beam and digital image correlation (FIB-DIC), which is able to deliver pointwise absolute measurement of residual stress. A set of FSW samples were then tested under uniaxial fatigue loading at several loading ranges, in the high cycle fatigue regime, in order to understand whether the severity of loads affects the crack path and life endurance. Fractographic and electron backscattered diffraction (EBSD) analysis then revealed crack nucleation site and propagation mechanisms with the respect of the underlying microstructure. Outcome of these experimental studies is then thoroughly discussed.

In this paper, the effect of equal channel angular pressing (ECAP) on microstructure and mechanical properties of hypereutectic Al-20%Mg2Si and Al-15%Mg2Si, as well as hypoeutectic Al-10%Mg2Si composites has been investigated. After fabricating the composites by in-situ casting, the composites were processed using the ECAP process up to two passes at room temperature. Microstructural studies have been carried out using a field emission scanning electron microscopy equipped with an energy dispersive X-ray spectrometer. Mechanical properties were also documented using Vickers microhardness and shear punch tests. In the hypereutectic composites, a decrease in the average size of pro-eutectic Mg2Si (Mg2Sip) particles, breakages in eutectic networks, and lengthening of the Al (&alpha, ) phase in direction of shear bands were observed after the ECAP process. For instance, the average size of Mg2Sip Particles in Al-20%Mg2Si composite reduced from 40 to 17 &mu, m after 2 passes of ECAP. Furthermore, a uniform distribution of Mg2Sip particles was developed in the matrix. In hypoeutectic composite, the ECAP process caused a uniform distribution of eutectic Mg2Si (Mg2SiE) in the matrix that considered a favorable microstructure. Microhardness measurements and shear punch results showed an ascending trend after each pass of ECAP for all specimens. For example, microhardness and shear strength of Al-20%Mg2Si increased from 88 HV and 109 MPa to 119 HV and 249 MPa after two passes indicating 35% and 34% increments, respectively. Density and porosity calculations by Archimedes principle revealed that the density of the composites increased after two passes of ECAP due to the reduction of porosity.

In the present study, aluminum alloy AA2219-T87 bars were cryorolled to various amounts of deformation in two pre-deformation conditions: (1) without solution treatment i.e., as-received T87 (WST-CR) and (2) with solution treatment (ST + CR). The solution treated and cryorolled bars were further annealed leading to a third condition: (3) solution treated, cryorolled, and annealed (CR + Annealed). Room-temperature mechanical properties have been evaluated for all three cryorolled conditions. Significant improvement in the 0.2 pct YS and UTS values was obtained for bars cryorolled to cross-sectional area reduction of more than 50 pct in the solution-treated condition (ST + CR), whereas for bars cryorolled in the without solution-treated condition (WST-CR), only an improvement in the 0.2 pct YS was observed. Cryorolling did not enhance the precipitation kinetics nor did it increase the response of the alloy to aging. The mechanical properties were correlated to the microstructures obtained by optical and transmission electron microscopy. Microstructural evolution in the ST + CR condition indicated gradual progression of the principal restoration mechanism from dynamic recovery (DRV) to dynamic recrystallization with an increasing amount of plastic deformation. Transmission electron microscopy of WST-CR and ST + CR specimens showed an increase in dislocation density as a function of the amount of deformation indicating suppression of DRV at cryogenic temperatures. Cryorolling in the solution-treated condition to cross-sectional area reduction of more than 50 pct (ST + 70 pct CR) was found to impart an optimum combination of strength and percent elongation in the present study., by Aditya Sarkar, K. Saravanan, Niraj Nayan, S. V. S. Narayana Murty, P. Ramesh Narayanan, P. V. Venkitakrishnan and Jyoti Mukhopadhyay

Softening frequently occurs in dual-phase steels under isothermal tempering of martensite. Recently, non-isothermal tempering is implemented to decrease the softening process in dual-phase steels. Here, we have discovered using high power electropulsing treatment can significantly enhance the strengthening effects via the formation of ultrafine-grained ferrite with nano-cementite particles in tempered martensitic-ferritic steels. To the best our knowledge, electropulsing treatment is a proper candidate to retard even to recovery the softening problems in the tempering of martensite in comparison with other isothermal and non-isothermal tempering methods.

There is a lack of information with regards to the friction effect in ECAPed aluminum alloys, even though it might substantially modify the deformation at the surface. In this work, the friction effect at the surface and the deformation heterogeneity in the ECAPed aluminum alloy 6061-T6 were characterized. X-Ray diffraction was used to determine residual stresses (RS) on the sample surface. The volumetric sections were characterized by Synchrotron diffraction at ESRF beamline ID15B (Grenoble, France). It was found that the microhardness mapping and residual stress results showed a good agreement with the finite element analysis for the first layer studied. Minor strain variation, Delta d/d as a function of (hkl) planes, for the different analyzed sections was found. The study also showed that there was an incomplete symmetry in the residual stress near the surface, even at up to a depth of 400 gm. The regions with higher deformation were found to be at the top and bottom parts of the sample, while the central region showed stress variations of up to 50 MPa. (C) 2016 Elsevier B.V. All rights reserved.

An extruded Mg–6Gd−3Y−0.5Ag magnesium alloy was processed by the simple shear extrusion (SSE) technique at 553 K for 1, 2, 4 and 6 passes to refine the microstructure. The electron back scattered diffraction (EBSD) analysis was used to investigate the microstructural evolutions of the alloy after the SSE processing. The grain orientation spread (GOS) maps revealed that by increasing the SSE passes, the fraction of the fine dynamically recrystallized (DRXed) grains increased accordingly from 3% after 1 pass of SSE to about 81% after 6 passes. The fraction of low angle grain boundaries (LAGBs) was relatively high in the early stages of the SSE processing, due to occurrence of dynamic recovery (DRV), but it began to drop significantly after 4 and 6 SSE passes, as the DRX proceeded. Therefore, continuous dynamic recrystallization (CDRX) was identified as the governing recrystallization mechanism during SSE at 553 K. The shear punch testing (SPT) was carried out at different temperatures and under various shear strain rates to assess the superplastic behavior of the alloys. It was found that only the alloy processed by 6 SSE passes exhibited superplastic flow, for which a maximum strain rate sensitivity (SRS) index of 0.45 and an average activation energy of 112 kJ mol−1 were obtained. Accordingly, grain boundary sliding (GBS) associated with the diffusion of grain boundaries was suggested to be the prevalent deformation mechanism during the superplastic flow of the 6-pass SSEed condition. Moreover, the SPT results revealed that as the SSE pass number increases the maximum SRS indices increase and shift to the lower temperatures indicating the rise in the contribution of the GBS mechanism. The kernel average misorientation (KAM) maps delineated that after SPT at 623 K the fine equi-axed DRXed grains were almost strain-free without any change in their shape for the 6-pass SSEed condition, while the one after 2 SSE passes was comprised of extremely deformed grains along the SPT loading direction.

Two types of A356 alloy castings in initial and modified with nanoparticles condition produced by gravitational casting were studied. Samples, as-cut from the castings, were subjected to light optical microscopy (LM), thermal analyses, Electron Backscattered Diffraction (EBSD) and Scanning Transmission Electron Microscopy (STEM) analyses. Results, obtained by EBSD, confirmed that there is grain refinement in samples from castings with added nanoparticles compared to the initial ones. STEM analysis shows agglomerates of nanoparticles in examined foils. Nanoparticles&rsquo, position in the microstructure confirms the hypothesis that they act as nucleating sites during the alloy solidification, which is the reason for observed fine-grained microstructure.

The homogenous redistribution of nanosized TiB2 particles in a fine-grained in-situ AA6063/TiB2 composite has been achieved by friction stir processing (FSP). The effects of TiB2 particles on as-deformed structure in the nugget zone and its thermal stability after additional T6 heat treatment are quantitatively evaluated by using neutron diffraction, scanning electron microscopy associated with electron backscatter diffraction and synchrotron X-ray line profile analysis. The results are compared to those obtained from a FSPed AA6063 alloy and, show first that, average grain size of the FSPed AA6063/TiB2 composite is smaller than that of the FSPed AA6063 alloy, while grain size distribution is more uniform. Second, dislocation density estimated in the FSPed AA6063/TiB2 composite is higher than that in the FSPed AA6063 alloy. Third, a small number of grains are dynamically recrystallized in the FSPed AA6063/TiB2 composite compared to its alloy counterpart, which indicates that recrystallization and grain growth during FSP and T6 heat treatment are effectively inhibited by the presence of nanosized TiB2 particles. Keywords: Metal-matrix composites (MMCs), X-ray diffraction (XRD), Transmission electron microscopy (TEM), Neutron diffraction, Friction stir processing

Wavy roll design was employed for strengthening 1 mm thin austenitic stainless steel coil sheet by cold rolling without further reduction in thickness. This steel possesses high corrosion resistance and high ductility. Initially, the sheets were rolled into sine wave shape (wave amplitude

Mg-3Al-1Zn (AZ31) alloy was caliber rolled isothermally in the temperature range of 523 K to 723 K (250 A degrees C to 450 A degrees C) to develop fine grains of 3 to 13 A mu m. Tensile tests by constant initial strain rate as well as differential strain rate test techniques were conducted over the temperature range of 493 K to 723 K (220 A degrees C to 450 A degrees C) and strain rate range of 10(-5) to 10(-1) s(-1). Maximum tensile elongation of 182 pct was obtained at test temperature of 723 K (450 A degrees C) and strain rate of 10(-3) s(-1) in the sample obtained from caliber rolling at 723 K (450 A degrees C), in spite of its large grain size of 13 A mu m. The strain rate sensitivity index 'm' was found to vary from 0.08 to 0.33 and activation energy for deformation 'Q' varied from 30 to 185 kJ mol(-1) depending on test condition and caliber-rolling condition. These variations in m and Q values are explained by the difference in prior grain size, texture, and twins developed as a function of caliber-rolling temperature, and further by the concomitant microstructural change occurring during tensile test itself. The presence of twins and orientation of grains influences the parameters of the constitutive relation to varying extent.

While many aspects of electronics manufacturing are controlled with great precision, the nucleation of tin in solder joints is currently left to chance. This leads to a widely varying melt undercooling and different crystal orientations in each joint, which results in a different resistance to electromigration, thermomechanical fatigue, and other failure modes in each joint. Here we identify a family of nucleants for tin, prove their effectiveness using a novel droplet solidification technique, and demonstrate an approach to incorporate the nucleants into solder joints to control the orientation of the tin nucleation event. With this approach, it is possible to change tin nucleation from a stochastic to a deterministic process, and to generate single-crystal joints with their c-axis orientation tailored to best combat a selected failure mode., Control over the crystallographic orientation of solder joints based on βSn will improve the reliability of electronic interconnects. Using a technique based on droplet solidification and lattice matching, Ma et al. are able to control the βSn nucleation events, hence control the grain orientation.

A Cu6Sn5 layer is an integral part of many electronic interconnections. Here we show that, although primary Cu6Sn5 is not a potent nucleant for Sn, the Cu6Sn5 layer plays a key role in Sn nucleation and microstructure formation in solder joints. Combining thermal analysis, FIB-tomography and EBSD, we show that conical cavities are present between the scallops of the Cu6Sn5 layer that act as geometric nucleation sites for Sn, that Sn grows from the Cu6Sn5 layer, and that reproducible nucleation orientation relationships (ORs) exist between Cu6Sn5 and Sn. With these ORs, a near-random distribution of Sn orientations is predicted from joint to joint even for Cu6Sn5 layers with a strong [0001] fibre texture. It is shown that the nucleation undercooling is strongly affected by manipulation of the Cu6Sn5 layer shape, and that it is possible to prevent nucleation on the Cu6Sn5 layer by adding more potent nucleants.

Repeated stress-relaxation experiments are conducted from RT to 1073 K on three different gamma + alpha(2) TiAl alloys (Ti-46Al with 8Ta, 8Nb or 7Nb) One is a conventional duplex alloy, the two other are novel "convoluted" cast titanium aluminides developed for turbine applications The data include measurements of the flow stress and activation volume of these alloys at 293, 673, 873, 923, 1023 and 1073 K. Despite differences in composition, processing and microstructure, the values and evolution with temperature or with stress of these parameters are relatively similar for the three alloys This observation, coupled with the agreement of present results with data in the literature for similar alloys, leads to conclude that the strain-rate dependence of plastic flow in alloys of this class is governed by features of the gamma-phase that are relatively insensitive to the alpha 2 phase morphology. The convoluted alloys furthermore feature a yield stress anomaly. (C) 2010 Elsevier Ltd All rights reserved.

The microstructure and mechanical properties improve substantially by hot working. This aspect in as-cast Mg-7.7Al-0.4Zn (AZ80) alloy is investigated by compression tests over temperature range of 30-439A degrees C and at strain rates of 5 x 10(-2), 10(-2), 5 x 10(-4) and 10(-4) s(-1). The stress exponent (n) and activation energy (Q) were evaluated and analyzed for high-temperature deformation along with the microstructures. Upon deformation to a true strain of 0.80, which corresponds to the pseudo-steady-state condition, n and Q were found to be 5 and 151 kJ/mol, respectively. This suggests the dislocation climb-controlled mechanism for deformation. Prior to attaining the pseudo-steady-state condition, the stress-strain curves of AZ80 Mg alloy exhibit flow hardening followed by flow softening depending on the test temperature and strain rate. The microstructures obtained upon deformation revealed dissolution of Mg17Al12 particles with concurrent grain growth of alpha-matrix. The parameters like strain rate sensitivity and activation energy were analyzed for describing the microstructure evolution also as a function of strain rate and temperature. This exhibited similar trend as seen for deformation per se. Thus, the mechanisms for deformation and microstructure evolution are suggested to be interdependent.

Ti + Nb-stabilised interstitial-free steel is deformed by equal-channel angular pressing (ECAP) adopting a route BC up to an equivalent strain of 24. Upon ECAP the grain size decreases to ultrafine level and it becomes strongly textured. At evm = 0.6-6, components of both {110} fiber, $$ J_{\uptheta } $$ , $$ \bar{J}_{\uptheta } $$ and of 〈111〉 fiber, D 1θ, D 2θ with common components of E θ, $$ \bar{E}_{\uptheta } $$ are existing but after evm ≥9, only 〈111〉 fiber components are observed. At large strain, evm = 9-24, 〈111〉 fiber texture is recorded with monoclinic symmetry. At evm = 0.6, coarse grains get split into deformation bands. Fragmentation of bands (at evm = 3) suppress $$ \bar{J}_{\uptheta } , $$ $$ J_{\uptheta } $$ components. At evm = 6, formation of lamellar structures increases intensity of mainly D 1θ, D 2θ. At evm = 9, oriented ribbon grains result in strong D 1θ, D 2θ components with 〈111〉 fiber. At evm = 15-24, conversion of ribbon grains to near-equiaxed shaped grains maintains 〈111〉 fiber texture with enhanced intensity of D 1θ and D 2θ components.

Modern concepts of the structure of liquid metals and alloys are analyzed, Several types of microinhomogeneity and microheterogeneity, of liquid metallic solutions are shown to exist. Their structure depends an their composition and pre-history Si. Using temperature and pressure variations and/or other physical effects, one can modify the structure. These changes retain down to liquidus and affect the structure and properties of the solidified alloy if the melt is cooled at appropriate cooling rate. This investigation focus on the effects of melt overheating above the liquids, Optimal thermal melting modes are specified using the results on liquid alloys structure and properties. Such optimized thermal treatment of melts (OTTM) is shown to be most efficient for rapidly quenched (RQ) metallic materials, The OTTM effects upon the structure and properties of amorphous ribbons, bulk amorphous alloys and,glass coated microwires are analyzed. (C) 2001 Elsevier Science B.V, All lights reserved.

The fundamental objective of the present work consists of the improvement of the plastic strain ratio (R-values) of AA-5182 aluminium alloy through improving the crystallographic texture by asymmetric rolling (ASR). The ASR process imposes intense shear deformation across the thickness of the sheet samples, leading to shear texture development. Finite element (FE) simulations of the ASR were first performed in order to investigate the impact of process parameters on the onset and growth of shear deformation throughout the thickness of sheet samples. In the present work, polycrystal simulations were also done to predict the texture evolutions and the mechanical response of the sheets deformed by different rolling processes. Afterwards, experimental studies were conducted. Conventional rolling (CR) as well as two types of ASR processes was carried out to reduce the thickness of the sheet samples. After each process, the rolled sheet samples were annealed. The crystallographic textures achieved in CR and ASR processes and annealing were measured. Furthermore, uniaxial tensile tests on the rolled sheets were also carried out in order to consider the effects of crystallographic texture on the macroscopic anisotropy. In agreement with the FE predictions, the experimental results showed that the shear strain spreads throughout the thickness of sheet samples during ASR and develops the shear texture. The mechanical behaviour and texture evolution predicted by numerical models are in good agreement with the experimental results. The modified texture leads to an increase of normal anisotropy as well as an increase of absolute value of planar anisotropy. (C) 2014 Elsevier B.V. All rights reserved.

Microstructural evolution and related dynamic recrystallization phenomena were investigated in overlapping multipass friction stir processing (FSP) of hypereutectic Al-30 pct Si alloy. FSP resulted in the elimination of porosities along with the refinement of primary silicon particles and alpha aluminum grains. These alpha aluminum grains predominantly exhibit high angle boundaries with various degrees of recovered substructure and dislocation densities. The substructure and grain formation during FSP take place primarily by annihilation and reorganization of dislocations in the grain interior and at low angle grain boundary. During multipass overlap FSP, small second phase particles were observed to form, which are accountable for pinning the grain boundaries and thus restricting their growth. During the multipass overlap FSP, the microstructure undergoes continuous dynamic recrystallization by formation of the subgrain boundary and subgrain growth to the grain structure comprising of mostly high angle grain boundaries.

Copyright @ 2013 ASM International. This paper was published in Metallurgical and Materials Transactions A, 44A(7), 3185 - 3197 and is made available as an electronic reprint with the permission of ASM International. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplications of any material in this paper for a fee or for commercial purposes, or modification of the content of this paper are prohibited. Microstructural evolution and solidification behavior of Al-5 wt pct Mg-1.5 wt pct Si-0.6 wt pct Mn-0.2 wt pct Ti alloy have been investigated using high-pressure die casting. Solidification commences with the formation of primary a-Al phase in the shot sleeve and is completed in the die cavity. The average size of dendrites and fragmented dendrites of the primary a-Al phase formed in the shot sleeve is 43 lm, and the globular primary a-Al grains formed inside the die cavity is at a size of 7.5 lm. Solidification inside the die cavity also forms the lamellar Al-Mg2Si eutectic phase and the Fe-rich intermetallics. The size of the eutectic cells is about 10 lm, in which the lamellar a-Al phase is 0.41 lm thick. The Fe-rich intermetallic compound exhibits a compact morphology and is less than 2 lm with a composition of 1.62 at. pct Si, 3.94 at. pct Fe, and 2.31 at. pct Mn. A solute-enriched circular band is always observed parallel to the surface of the casting. The band zone separates the outer skin region from the central region of the casting. The solute concentration is consistent in the skin region and shows a general drop toward the center inside the band for Mg and Si. The peak of the solute enrichment in the band zone is much higher than the nominal composition of the alloy. The die casting exhibits a combination of brittle and ductile fracture. There is no significant difference on the fracture morphology in the three regions. The band zone is not significantly detrimental in terms of the fracture mechanism in the die casting. Calculations using the Mullins and Sekerka stability criterion reveal that the solidification of the primary a-Al phase inside the die cavity has been completed before the spherical a-Al globules begin to lose their stability, but the a-Al grains formed in the shot sleeve exceed the limit of spherical growth and therefore exhibit a dendritic morphology EPSRC and JLR

The microstructure and texture evolution of cold-rolled low carbon steel after ultrafast heating and quenching is investigated. Experiments were carried out at heating rates of 150 degrees C/s and 1500 degrees C/s. The recrystallization of ferrite is studied by scanning electron microscopy and electron backscattered diffraction techniques. The texture evolution of cold rolled steel during ultrafast heating was studied, making it possible to estimate the precise effect of heating rate on the orientations of newly formed grains. The experimental results showed that the recrystallization of ferrite was not completed before the full transformation of austenite. The noticeable increase in the fraction of recrystallized grains of diameter less than 1 mu m, when the heating rate is increased from 150 degrees C/s to 1500 degrees C/s suggests that the increase of the heating rate enhances the nucleation of ferrite. The crystallographic orientations in recrystallized ferrite are strongly influenced by the heating rates. The effect of heating rate in the releasing of stored energy, carbon diffusion and spheroidization of cementite might explain some differences in textures observed in recrystallized ferrite.