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To examine the austenite grain growth behavior and kinetics under isothermal austenitization process in a low alloy medium carbon forged steel, heat treatments at different temperatures (1150, 1175, 1200, and 1260 °C) and times (5, 15, and 25 min) were conducted. An Arrhenius constitutive relationship was developed to analyze and predict the austenite grain size as a function of the austenitization temperature and time during isothermal austenitization. The model predictions agreed well with the experimental austenite grain size data. Following the austenitization examinations, the hot deformation behavior of the alloy was studied by performing isothermal compression tests for different soaking times (5, 15, and 25 min) at the deformation temperatures of 1150, 1175, and 1200 °C, at a constant strain rate of 0.05 s−1, and up to a true strain of 0.6. The microstructures of the hot compressed samples were assessed to determine the dynamic softening mechanisms and potential austenite grain refinement by dynamic recrystallization (DRX). Under the investigated hot deformation conditions, the flow stress curves and microstructure observations showed DRX characteristics. The flow curves from the peak to the steady-state stress were accurately predicted using a Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation. Based on the flow curves and a mathematical equation, the DRX kinetics were also determined. Variations of the flow curves, DRX kinetics, and dynamic recrystallized (DRXed) grain size with the deformation temperature, strain, and the austenite grain size prior to deformation were analyzed.

The microstructure, microhardness, tensile properties, and fracture characteristics of the laser welded Ti–10V–2Fe–3Al (Ti1023) titanium alloy in the as-welded condition were examined. The mechanical properties were related to the microstructure development across the weld. In the base material (BM), the primary α phase with spherical and lath morphologies was dispersed in the β matrix. The volume fraction of the α phase in the heat affected zone (HAZ) decreased to some extent compared to the BM as a result of its partial dissolution and/or transformation to the β phase. In the fusion zone (FZ), primary α phase was completely transformed to the β phase. The BM exhibited a higher hardness than HAZ and FZ due to a higher volume fraction of the primary α phase, which is harder than β phase. The yield strength (YS) and ultimate tensile strength (UTS) of the weldments were somewhat lower than those of the BM due to the presence of a softer phase in the FZ and a lower volume fraction of the α phase in the HAZ. Also, the presence of porosity, undercut, concavity, and coarse columnar β grains in the FZ contributed to lower YS, UTS, and total elongation in the weldments in comparison to the unwelded material. Examination of the fracture surface in the weldment tensile samples indicated a mixed brittle and ductile fracture mode.

A constitutive model for aluminum alloys under hot working conditions is proposed. The elastic-viscoplastic model is implemented in a finite strain continuum mechanical framework. The model accounts for the interplay between dynamic recovery and recrystallization during hot working of aluminum alloys and central aspects of microstructure evolution such as grain/subgrain size and dislocation density. The proposed model is generic in the sense that it can be used for arbitrary aluminum alloys, but in order to demonstrate its capabilities, the model is calibrated to a newly developed AA6099 alloy in the present study. The model is thoroughly discussed and details on the numerical implementation as well as on the calibration of the model against experimental data are provided.

In this work, the inhibition efficiency of an imidazoline derivative corrosion inhibitors in CO2 corrosion of carbon steel was investigated in the presence of iron carbonate scale and hydrogen sulfide. The use of corrosion inhibitors is one of the most common controlling techniques for CO2 corrosion of carbon steel in oil and gas industry. One of the imidazoline derivatives was used as a corrosion inhibitor which protects the surface through the film formation mechanism. The investigation material was API 5L X65 carbon steel which was cut from a wet gas transmission pipeline. The internal surface of the pipe was covered with iron carbonate as corrosion product. In order to investigate the inhibitor efficiency, Tafel polarization and electrochemical impedance spectroscopy were done in CO2-saturated 3.5 wt.% sodium chloride solution. According to the results, the existence of iron carbonate film reduced the inhibition efficiency. Furthermore, it was found that in the presence of H2S gas, the inhibition efficiency was decreased due to the decrease in inhibitor adsorption on the surface.

The hot deformation behavior of a newly developed AA6099 alloy was investigated after homogenization. To this end, Gleeble® isothermal hot compression tests were performed at temperatures of 350, 400, 450, and 500 °C, and strain rates of 0.01, 0.1, and 1 s−1 up to a true strain of 0.8. The dependency of the flow stress on the deformation temperature, strain, and strain rate was analyzed. In addition, the constitutive equations relating the flow stress to the deformation temperature and strain rate were derived using a power-law empirical model. Also, the microstructures and dynamic softening mechanisms of the alloy under various deformation conditions were examined using light optical microscopy (LOM) and electron back scattered diffraction (EBSD) techniques. The correlation between the flow behavior, different microstructures, and dynamic softening mechanisms at various hot compression conditions was determined. The kinetic analysis and microstructural evolution indicated that the main flow softening mechanism for homogenized AA6099 was dynamic recovery (DRV). Partial dynamic recrystallization (DRX) enhanced the flow softening especially at low deformation temperatures and high strain rates, i.e., at high Zener-Hollomon parameter (Z) values.

Metallurgical and mechanical characterization of surface and subsurface regions in broached and shot-peened fir-trees in an industrial gas turbine disc made of Inconel-718 were carried out. High resolution scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectrometry (EDS), electron backscatter diffraction (EBSD), X-ray diffraction, optical microscopy, and microhardness instruments were employed for qualitative and quantitative assessment of alterations at surface and subsurface levels. Five specific locations along the broached and shot-peened path were selected and thoroughly examined. Original metallography methods were developed to clearly and reliably reveal microstructure constituents. Special emphasis was placed on the generated defects in view of the manufacturer's quality indices, formation mechanisms of defects, and their potential impact on the service capability of the disc. Also, advanced analysis of the EBSD data allowed assessment of the deformed layer thickness as well as the misorientation angle and grain size variations from the broached and shot-peened surface towards the bulk parent material (PM). Furthermore, through successive material removal by electropolishing, measurement of residual stresses as a function of depth from the surface was performed by the sin 2 Ψ method. The obtained results are analyzed in terms of impact of the processing conditions on the evolution of microstructure, microhardness, and residual stresses. The findings are also related to the geometrical location in the disc.

Electron beam welding (EBW) of shrouds in Inconel-713LC low-pressure gas turbine blades has been associated with cracking in fusion zone (FZ) and heat affected zone (HAZ) leading to a high-scrap rate in manufacturing of gas turbine blades. A comprehensive numerical analysis have been carried out using ABAQUS software to predict the level of thermal and residual stresses as well as distortions in FZ and HAZ of the electron beam welded shrouds. A particular effort has been made to develop an accurate model for the heat input since it has a significant influence on temperature distribution and has a direct correlation with the melt pool shape. As a result of the analysis, it was observed that the highest residual stress arises in FZ and HAZ boundary. Furthermore, it was concluded that the cosmetic pass narrows down the high-stress region. To reduce the level of tensile stresses, which are known as main cracking causes in FZ and HAZ, it is imperative to understand the influence of weld parameters on the residual stresses. To this end, a sensitivity analysis was carried out and the impact of EBW process parameters on temperature distribution, residual stress, and distortion were determined. From the numerical calculations, it was concluded that higher amount of power results in larger size of HAZ, wider regions exposed to tensile residual stresses and higher distortions. On the other hand, by increasing the welding speed, the amount of heat input is decreased which results in lower keyhole temperature, smaller size of HAZ, narrower regions exposed to tensile residual stresses, and lower amount of distortions.

Hot single point incremental forming (SPIF) with induction heating and cryogenic cooling has been applied to form the Ti-6Al-4V sheets. The influence of both the forming temperature and the cooling rate after deformation, on microstructure evolution and microhardness of Ti-6Al-4V sheets, has been extensively studied. We propose the use and development of a new system of heating by induction. The system is composed of a medium–high frequency generator and a continuously water-cooled heating head, which is placed under the sheet and linked axially to the punch movement, heating the material locally by generating an eddy current within the material. Furthermore, a cooling system integrated with the movement of the forming punch allows us to apply a cryogenic fluid to the recently deformed sheet metal. Both localized heating and cooling systems are particularly suitable for such a process as SPIF, whose primary characteristic is the incremental forming of localized sheet zones. The meta-dynamic and static recrystallization processes have been suppressed in the sheet material, evident by the final microstructure and mechanical properties. Finally, a comparison between parts is made, both with and without cooling during hot SPIF.

Room temperature tensile properties and microhardness of a laser welded Ti–6Al–2Sn–4Zr–2Mo (Ti6242) titanium alloy sheet were examined and correlated to the microstructure evolution across the weld. Tensile testing integrated with the optical image correlation Instron® system indicated that the average yield strength (YS), ultimate tensile strength (UTS), and total elongation of the weldment were respectively 88%, 87%, and 69% of the corresponding base material (BM) values. Electron probe microanalysis (EPMA) demonstrated a uniform distribution of the main alloying elements across the weld. The hardness raised increasingly from the BM toward the heat affected zone (HAZ) and the fusion zone (FZ) due to mainly a higher α volume fraction in HAZ and acicular α′ martensite formation in the FZ. Because of the higher hardness of the HAZ and FZ, a higher YS for the weldment relative to the BM would be expected. However, the lower YS as well as the lower UTS of the weldment can be explained by presence of some porosity and underfill in the FZ. The lower total elongation of the weldment compared to the BM can be related to the higher hardness of the HAZ and FZ.

Electron beam welding (EBW) of shrouds in Inconel-713LC low pressure gas turbine blades was associated with cracking in fusion zone (FZ) and heat affected zone (HAZ) leading to a high scrap rate in manufacturing of gas turbine blades. In this study, in order to develop a detailed map of cracks and understand the root cause of cracking, a comprehensive microstructural and numerical analysis was performed. The elemental mapping in scanning electron microscope (SEM)-energy dispersive spectral analysis revealed segregation of alloying elements in the cracked area of FZ and HAZ. In other words, one of the cracking mechanisms in FZ and HAZ was found to be segregation induced liquation and subsequent cracking due to thermal and mechanical tensile stresses generated during EBW. Cracking in FZ also occurred because of low strength of the solidifying weld metal as well as solidification contraction. As well, γ ′ dissolution and reprecipitation in HAZ leading to decreased ductility and generation of contraction stresses was another mechanism for cracking in HAZ. The numerical model was capable to predict the cracking location as well as cracking orientation with respect to the weld line.

Inertia and linear friction welding are being increasingly used for near-net-shape manufacturing of high-value materials in aerospace and power generation gas turbines because of providing a better quality joint and offering many advantages over conventional fusion welding and mechanical joining techniques. In this paper, the published works up-to-date on inertia and linear friction welding of Ni-based superalloys are reviewed with the objective to make clarifications on discrepancies and uncertainties reported in literature regarding issues related to these two friction welding processes as well as microstructure, texture, and mechanical properties of the Ni-based superalloy weldments. Initially, the chemical composition and microstructure of Ni-based superalloys that contribute to the quality of the joint are reviewed briefly. Then, problems related to fusion welding of these alloys are addressed with due consideration of inertia and linear friction welding as alternative techniques. The fundamentals of inertia and linear friction welding processes are analyzed next with emphasis on the bonding mechanisms and evolution of temperature and strain rate across the weld interface. Microstructural features, texture development, residual stresses, and mechanical properties of similar and dissimilar polycrystalline and single crystal Ni-based superalloy weldments are discussed next. Then, application of inertia and linear friction welding for joining Ni-based superalloys and related advantages over fusion welding, mechanical joining, and machining are explained briefly. Finally, present scientific and technological challenges facing inertia and linear friction welding of Ni-based superalloys including those related to modeling of these processes are addressed.

The evolution of the flow stress and microstructure for Waspaloy was studied in the 950–1140 °C temperature range under constant true strain rate conditions of 0.001–1 s −1 up to a true strain of 0.83 using isothermal hot compression testing. The impact of friction at the sample/anvil interface and adiabatic heating during deformation on the flow stress evolution was also examined. Mathematical models relating the flow stress to the deformation temperature and strain rate were derived using a power–law relationship. The strain rate sensitivity and the activation energy for hot deformation of Waspaloy were found to be considerably different for deformation in the subsolvus and supersolvus temperature ranges. According to the microstructural investigations, at 950 °C dynamic recovery (DRV) was the main softening mechanism. By contrast, dynamic recrystallization (DRX), partial or complete, occurred at temperatures above 950 °C and resulted in flow softening.

A finite element model was developed for isothermal forging of a nickel-base superalloy, Waspaloy, using DEFORM® simulation software. The effects of the forging temperature in the 980 to 1140 °C range, strain rate in the 0.01–1 s−1 range, and true strain up to 0.83, on the hot deformation behavior and microstructure evolution were examined. The model was validated by comparing the predictions with the experimentally measured true stress–true strain curves and the average grain sizes. Reasonable agreement was obtained between the predictions and experimental data. The modeling results show that under investigated conditions the distributions of hot deformation parameters, i.e., strain, strain rate, and temperature, were inhomogeneous within the forging. The maximum strain, strain rate, and temperature were mainly observed at the edge and center of the forging. The inhomogeneous deformation resulted in the development of the dead metal zones close to the dies and an inhomogeneous microstructure, i.e., inhomogeneous distribution of dynamic recrystallization (DRX) volume fraction and average grain size, in the forging.

Microstructure evolution from center to edge of the as-forged and heat treated Inconel-718 disks was investigated. Specifically, the evolution of primary carbides, grain size, γ ″, γ ′, δ , and secondary carbide particles was the focus of the current study. In fact, characterization of these microstructure features is essential for models predicting the creep and fatigue lives of the alloy. Accurate and reliable revealing of the grain boundaries in as-forged and heat treated Inconel-718 was made possible in this study by development of a new method. From microstructure investigations, nonuniformities in grain size, volume fraction, size and inter particle spacing of precipitates from center to edge were observed in both as-forged and heat treated disks. The microstructure nonuniformities resulted in significant variation in hardness from center to edge of the disks.

The mechanical properties and microstructural evolution of WASPALOY joined by linear friction welding (LFW) were investigated in this study. In-situ temperature measurements using thermocouple probes indicated exposure of the weld area to a temperature of at least 1400 K (1126 °C). Based on electron backscatter diffraction (EBSD) mapping of the weldments, up to 50 pct reduction in γ grain size occurred within 0.9 mm of the weld interface as a result of dynamic recrystallization (DRX). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies revealed that progressive dissolution of γ′ precipitates took place from the base metal to the weld interface, where almost no γ′ precipitates were observed. Within 3.3 mm of the weld interface, the γ′ dissolution significantly influenced the hardness profile measured across the extended thermomechanically affected zones (TMAZs). Investigation of strain distributions during tensile testing using the optical Aramis system revealed weak bonding at the edge of the weld due to oxidation. To extrude out oxide layers into the flash, increasing the axial shortening to higher than 1.2 mm is recommended.

TMS 2011 Annual Meeting and Exhibition, 2011, San Diego, USA

Nickel-base superalloy, Waspaloy, was linear friction welded (LFWed) under different axial shortening conditions of 2.0, 3.4, and 4.6 mm. The tensile properties and microhardness of the weldments were investigated in the as-LFWed condition and compared with those in the post-weld heat treated (PWHTed) condition. Mechanical properties were related to microstructures following examination by optical microscopy, high resolution scanning electron microscopy, and electron backscatter diffraction (EBSD). Analyses of the EBSD results in terms of the misorientation angle distribution, which represents the stored energy, were performed. In the as-LFWed condition, the yield strength (YS) and ultimate tensile strength (UTS) increased with axial shortening due to greater expulsion of the softened interfacial material toward the periphery as flash. In contrast, with increasing axial shortening the total elongation initially remained constant and then decreased. This was also related to the expulsion of the softened interfacial material into the bifurcated flash. Extensive dissolution of the strengthening phase (γ′) in the weld area during linear friction welding (LFW) contributed to the lower YS and UTS in the as-welded condition compared to the PWHTed condition where the γ′ particles were recovered. After performing post-weld heat treatment (PWHT), the total elongation improved due to the relaxation of storedmore » energy and grain growth in the thermomechanically affected zone (TMAZ). - Highlights: • Tensile property and microstructure in Waspaloy linear friction welds were studied. • Yield strength and ultimate tensile strength increased with axial shortening. • Elongation initially remained constant and then decreased with axial shortening. • Post-weld heat treat recovered dissolved γ′ particles and increased weld strength. • Stored energy relaxation during post-weld heat treatment improved weld elongation.« less

The effects of gage length, width measurement locations, and specimen geometry on plastic strain ratio have been investigated for the AA8011 aluminum alloy and interstitial-free (IF) steel sheets. The specimens were ASTM E 517 to 92a subsize, type A, and type A alternative with, respectively, 37.5, 76, and 57 mm reduced parallel sections and with different fillet radii. In each specimen type, there were differences in axial strains of gage marks and changes in width strain over the reduced parallel section, which depend on the applied axial strain, reduced parallel section legth, and fillet radius. Therefore, the magnitudes of the calculated R-values depend upon gage length, width measurement location, axial strain, and specimen geometry. These dependencies were more pronounced in the high R-value IF steel sheet relative to the low R-value AA8011 aluminum alloy sheet. The dependencies of R-value on gage length and width measurement location are negligible in all AA8011 specimens, while in IF specimens, these dependencies can be neglected only for type A specimens with 12.5-mm fillet radius. It is concluded that the observed differences in the measured R-values for specimens with different geometries can be attributed to the constraints imposed by the shoulders, which affect the width strain measurements and the resulting R-values.

Plastic strain ratios of AA8011 aluminum alloy and commercially pure titanium sheet with, respectively, low and high elastic spring-back were determined by digital imaging of marked tensile specimens with and without considering elastic strains. To calculate the actual R-values, a new method was proposed for the compensation of elastic strains. The essential feature in the approach proposed consists of defining elastic strains with respect to gage length before unloading. Comparison with experimental data shows that the new method is generally more accurate than the existing ones, especially in the cases where materials with very high elastic spring-back, such as titanium, are concerned. The results were discussed on the basis of elastic and yield behavior of the materials.

The effect of gage length, width measurement locations, and axial strain on plastic strain ratio have been investigated for commercially pure titanium sheet. The specimens were ASTM E 517-92a subsize, type A, and type A alternative. In general, slightly larger length strain values were observed for shorter gage marks. Because of differences in strains of gage lengths and width locations for each specimen type, the magnitude of the calculated R-value depends on the gage length and width measurement locations. Also, for a given gage length and width measurement location, the magnitude of the calculated plastic strain ratio and its variation with axial strain depends on specimen type. The type A specimen resulted in fewer changes in R-value with increased strain than either the subsize or type A alternative specimens.

Broaching has long been used for machining of fir-trees in gas turbine discs. The fir-tree arrangement is employed for mechanical attachment of blades to disc. Surface and subsurface microstructure changes induced by broaching affect the fatigue resistance of the disc. Therefore, a reliable and quantitative microstructure mapping of the broached fir-trees is essential for the basic optimization of the broaching process. In this study, the microstructure of the surface and subsurface layers of fir-trees in an industrial gas turbine Inconel-718 disc has been analyzed using optical microscopy and scanning electron microscopy. The focus has been on the characterization of defects generated by broaching at the surface and subsurface layers of fir-trees. Also, characterization of the grain size, γ″, γ′, and δ particles from the broached surface to the parent material has been carried out. Characteristics of these microstructural features are key inputs for the development of material based FEM models predicting the fatigue life of the disc. From microstructure studies, the presence of defects such as plucking and distorted layer was observed. The characteristics of these defects (size and morphology) were compared with those of the design limits determined by gas turbine engine manufacturer. Furthermore, significant variation in the volume fraction of δ particles was observed in the area affected by broaching compared with the parent material. These observations are related to the thermomechanical history of the material during the broaching process. Finally, the impact of microstructure evolution on microhardness variation from the broached surface to the parent material is discussed.

A creep Deformation Mechanism Map (DMM) of an engineering alloy can be an effective tool for developing physics based prognostics systems. Many classical diffusion based rate equations have been developed for time dependent plastic flow where dislocation glide, dislocation glide-plus-climb and vacancy diffusion driven grain boundary migration (diffusion creep) are rate controlling. Long term creep testing and analysis of complex engineering alloys has shown that power law breakdown phenomenon is related to the dominance of Grain Boundary Sliding (GBS) as opposed to diffusion creep. Rate equations are now available for GBS in complex alloys and, in this paper, a DMM is constructed for Waspaloy (a Nickel-Based Superalloy) and validated by comparison with a collection of experimental data obtained from the literature. The GBS accommodated by wedge type cracking is considered dominant at low homologous temperatures (0.3 to 0.5Tm - temperature in Kelvin) whereas GBS accommodated by power-law or cavitations creep dominates above 0.55Tm.Copyright © 2013 by ASME

The high-temperature deformation behavior of the Ni-base superalloy, Waspaloy, using uniaxial isothermal compression testing was investigated at temperatures above the γ′ solvus, 1333 K, 1373 K, 1413 K (1060 C, 1100 C, 1140 C) for constant true strain rates of 0.001, 0.01, 0.1, 1 s -1 and up to a true strain of 0.83. Flow softening and microstructural investigation indicated that dynamic recrystallization took place during deformation. For the investigated conditions, the strain rate sensitivity factor and the activation energy of hot deformation were 0.199 and 462 kJ/mol, respectively. Constitutive equations relating the dynamic recrystallized grain size to the deformation temperature and strain rate were developed and used to predict the grain size and strain rate in linear friction-welded (LFWed) Waspaloy. The predictions were validated against experimental findings and data reported in the literature. It was found that the equations can reliably predict the grain size of LFWed Waspaloy. Furthermore, the estimated strain rate was in agreement with finite element modeling data reported in the literature. © 2013 The Minerals, Metals & Materials Society and ASM International.

The Ni-base superalloy, Waspaloy, was linear friction welded (LFWed) under various processing parameters and then subjected to a post weld heat treatment (PWHT). Tensile testing integrated with the optical image correlation Aramis® system indicated that there is a critical axial shortening value (2 mm) below which LFWed and post weld heat treated (PWHTed) Waspaloy exhibited weak integrity. At and above this critical shortening, the yield strength and ultimate tensile stress (UTS) values were more or less the same as for the parent material. However, total elongation continued to increase with axial shortening even above the critical value due to decrease in width of thermo-mechanically affected zone (TMAZ). The sample with the highest axial shortening (4.9 mm) exhibited an elongation 91% of the parent material elongation. According to Aramis® data, the mixture rule can be used reliably to determine the contribution of TMAZ to the tensile elongation of PWHTed Waspaloy. Microstructure characterization across the weld in the as-LFWed and PWHTed conditions was carried out to correlate the process parameters and microstructural changes that affect the tensile properties. Weak integrity at axial shortening below 2 mm was mainly due to lack of bonding and/or presence of oxides at the weld interface. In the as-welded condition, a loss in hardness was observed, and related to the extensive dissolution of strengthening phase (γ′) in the weld area. The applied PWHT restored the hardness in the weld region.

Fusion welding of nickel-base superalloys is often associated with fusion zone solidification cracking and/or liquation induced heat affected zone (HAZ) cracking. As an alternative joining technology, linear friction welding (LFW) was used in the current study to join the nickel-base superalloy, WASPALOY. Under the experimental conditions used in the present investigation, the temperature data recorded by inserting thermocouples at different locations from the weld interface indicated that the temperature in the weld area reached up to 1280 °C, which is at least 50 °C below the melting point of the bulk alloy. However, this temperature is well above the liquation temperature of the low melting point components in the alloy (1245 °C). As a result, liquation may occur in linear friction welded (LFWed) WASPALOY. The occurrence of liquation and/or microcracking was investigated using optical microscopy (OM), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) X-ray mapping. The high pressure applied during the oscillation and forge phases of the LFW process and the resulting γ grain refinement contributed in preventing liquation and microcracking in the weldments. Furthermore, according to the SEM and X-ray mapping results, LFW altered the chemical composition, morphology and size of the γ′ precipitates at a location of 2 mm from the weld interface. It was determined that γ′ coalescence at 2 mm from the weld interface played a role in decreasing the microhardness (by 30%) relative to the base metal.

Over conventional joining methods, linear friction welding (LFW) exhibits a high weld quality and economical benefits for the aerospace industry. In particular, LFW enables the removal of the fir-tree in conventional blade to disk assembly, which results in weight reduction and improvement in engine efficiency. Considering these advantages, the LFW behavior of Waspaloy, used in jet engines as blade and disc material, has been investigated at different processing conditions. This study specifically highlights the influence of frequency, amplitude, and pressure during oscillation on the microstructure and mechanical properties of the welded samples. Microstructure and mechanical characteristics of the thermo-mechanically affected zones (TMAZ) were investigated by optical microscopy, EBSD, SEM, and microhardness. The LFW operating window resulting in welds free from defects was determined from these data. Microstructure examination revealed that dynamic recrystallization (DRX) occurred in the 0.9 mm narrow band of the TMAZ resulting in up to 50% reduction in the grain size. Furthermore, at the weld interface a considerable volume fraction of the ?' precipitates dissolved, contributing to a drop in hardness., Materials Science and Technology, October 25-29th 2009, Pittsburgh, USA