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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Comparison of structural and magnetic properties of Zn{sub x}Mg{sub 1.5-x}Mn{sub 0.5}FeO{sub 4} and MgAl{sub x}Cr{sub x}Fe{sub 2-2x}O{sub 4} spinel oxides

The spinel oxides Zn{sub x}Mg{sub 1.5-x}Mn{sub 0.5}FeO{sub 4} (x = 0.0 to 0.6) and MgAl{sub x}Cr{sub x}Fe{sub 2-2x}O{sub 4} (x = 0.0 to 0.6) abbreviated as ZMMFO and MACFO respectively, were synthesized by standard ceramic processing. The compositional purity of all the specimens was checked by EDAX technique. The X-ray diffractometry was employed to determine the lattice constants and distribution of cations in the interstitial voids. The initial decrease of cell edge parameter (a) for ZMMFO up to x = 0.2 and thereafter expected rise in the ‘a’ and the initial slower rate of reduction in the lattice constant for MACFO are explained as basic of cation occupancy. The magnetic ordering in both systems is explained by invoking statistical canting models. The compositional variation of magneton number (n{sub B}) for ZMMFO could be very well explained by Localized canting of spin (LCS) model while Random canting of spin (RCS) model was used for MACFO system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Interfacial Ferromagnetism in a Co/CdTe Ferromagnet/Semiconductor Quantum Well Hybrid Structure

The magnetization properties of a ferromagnet-semiconductor Co/CdMgTe/CdTe quantum well hybrid structure are investigated by several techniques. Exploiting the proximity effect between acceptor bound holes and magnetic ions we detect the magnetization curves by measuring the circular polarization of photoluminescence in an out-of-plane magnetic field. We show that magnetization originates from interfacial ferromagnet on Co-CdMgTe interface and the proximity effect is caused by magnetization of interfacial Co-CdMgTe ferromagnetic layer whose magnetic properties are very different from Co.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of Overaging on Fatigue Crack Propagation and Stress Corrosion Cracking Behaviors of an Al-Zn-Mg-Cu Alloy Thick Plate

The fatigue property as well as stress corrosion cracking (SCC) resistance of an Al-Zn-Mg-Cu alloy thick plate in peak-aged and overaged tempers (T7351 and T7651) is systematically investigated by fatigue crack propagation (FCP) test and slow strain rate test (SSRT). Microstructural characterization is examined by transmission electron microscopy and scanning electron microscopy. Results reveal that the T7351 alloy has lower strength but higher electrical conductivity as compared to T7651 alloy. The FCP resistance of T7351 alloy is superior to that of the T7651 alloy due to the coarser precipitates in the highly overaged alloy in which the strain localization is reduced by promoting homogeneous slip. In addition, the SSRT test suggests a higher SCC resistance in T7351 alloy. The enhanced SCC resistance is found to depend on grain boundary precipitate characteristics and crack propagation resistance of the alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Changes in the microstructure and mechanical properties of additively manufactured AlSi10Mg alloy after exposure to elevated temperatures

Highlights: • Elevated temperatures above 120 °C brought changes to the AM AlSi10Mg alloy. • A maximum hardness state obtained at 160 °C/5 h was thoroughly tested. • Hardness increased by 15% and TYS by 5%, but elongation dropped by 60%. • Pure Si precipitates were responsible for the observed changes. - Abstract: The additive manufacture (AM) of the AlSi10Mg alloy has become the subject of considerable attention, especially for production of complex parts in engines. Because such parts can be exposed to elevated temperatures during operation, material stability is very important, but as yet little is known about it in relation to AM. Here, we studied changes of the AlSi10Mg alloy produced by selective laser melting (SLM) after its exposure to temperatures between 120 and 180 °C. At each temperature, hardness evolution was measured, with hardness increasing over time. The maximum hardness state obtained at 160 °C was selected for further studies comprising microstructural analysis by scanning and transmission electron microscopy, chemical composition analysis and mechanical properties assessment. Transmission microscopy revealed nano-scale acicular precipitates that caused a slight increase in the yield strength of the alloy together with a significant drop in elongation. Electron energy loss spectroscopy (EELS) and energy dispersive spectroscopy (EDS) showed that the precipitates surprisingly consisted of pure Si. To provide a comparison, conventional regimes of heat treatment (stress-relief and T6) were applied. Despite a considerable loss in mechanical performance, thermal instability was no longer observed. Overall, our results indicate that operating temperatures are a key factor in ensuring the smooth operation of AM parts of the AlSi10Mg alloy. In respect to that, we offer recommendations for their industrial use.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of laser rescanning on the grain microstructure of a selective laser melted Al-Mg-Zr alloy

Highlights: • Laser rescanning of a new Al-Mg-Zr alloy was investigated. • SLM of the Al-Mg-Zr alloy results in a duplex grain structure. • Rescanning of the alloy results in a refinement of the microstructure. - Abstract: The microstructures of alloys created via Additive Manufacturing (AM) can vary substantially from those present in cast or wrought products, due to the very rapid solidification associated with AM. While numerous studies have investigated the process-microstructure relationship of alloys created by Selective Laser Melting (SLM), few have investigated the effects of laser rescanning to alter the microstructure or take advantage of the rapid solidification conditions the process provides. This study investigates the effect of single- or multiple pass laser scanning upon the grain structure of Addalloy™, a new Al-Mg-Zr alloy strengthened via L1{sub 2} Al{sub 3}Zr precipitates. The bottom of the melt pools consisted of fine equiaxed grains (1.3 μm) that nucleated from primary Al{sub 3}Zr (100–400 nm) precipitates. The top of the melt pool consists of columnar grains (up to 40 μm long), consistent with lack of Al{sub 3}Zr nucleants due to Zr solute trapping from increased solidification velocities. Additional laser scanning (a second or third scan) reduces the amounts of columnar grains and increased the number equiaxed grains. The change is attributed to a shallower melt pool remelting the columnar grain region upon rescanning, due to reduced laser energy absorption and increased heat losses in the solid.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Coincidence site lattice boundary mechanism for the preferred growth of Goss and Cube grains during annealing in an Al-Cu-Mg alloy

Highlights: • Both Goss and Cube grains are recrystallized out of Brass matrix. • Boundary character between Brass and Goss grains was Σ9, and that between Brass and Cube was Σ5. • Σ9 and Σ5 boundaries only transitionally appeared during recrystallization. • Temperature had decisive effect on the formation and mobility of CSL boundaries. • Σ9 and Σ5 boundaries with high index planes were highly mobile. - Abstract: The formation mechanism of recrystallized textures in an Al-Cu-Mg alloy was investigated by means of three dimensional orientation distribution functions (ODFs) and in-situ electron back-scattered diffraction (EBSD). The results showed that in the hot-rolled alloy with a very sharp Brass texture but weak Copper and S orientations, both Goss and Cube grains were recrystallized out of parent Brass matrix. In-situ EBSD analysis revealed that characteristic boundary between Brass and Goss grains to be Σ9, while that between Brass and Cube grains to be Σ5. Frequency of Σ9 and Σ5 boundaries increased quickly at early stage and then reduced gradually with the process of recrystallization. Annealing at a higher temperature (320 °C) was found to be beneficial for the formation of Σ9 boundary, while at lower one (300 °C), Σ5 boundary became dominant. Besides, with temperature decreasing from 320 to 300 °C, the mobility of Σ9 boundaries was greatly degraded, but relatively, Σ5 boundaries still behaved highly mobile. Principally, the preferred growth of recrystallized Goss and Cube grains was respectively attributed to the high mobility of Σ9 and Σ5 boundaries with high index planes that the square sum of plane index was larger than 3.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Dependence of microwave dielectric properties on crystallization behaviour of CaMgSi{sub 2}O{sub 6} glass-ceramics

The effects of the crystallization behaviour of CaMgSi{sub 2}O{sub 6} (diopside) glass-ceramics on their microwave dielectric properties were investigated as functions of the Cr{sub 2}O{sub 3} content and heat-treatment method used (one or two steps). The crystallization behaviours of the specimens were affected by the Cr{sub 2}O{sub 3} content as well as by the heat-treatment method employed, and were evaluated using X-ray diffraction and the combined Rietveld and reference intensity ratio (RIR) method. The dielectric constants (K) of the specimens did not change significantly with an increase in the Cr{sub 2}O{sub 3} content. The quality factor (Qf) of the specimens increased for Cr{sub 2}O{sub 3} contents of up to 0.5 wt% Cr{sub 2}O{sub 3}, but then decreased for higher contents. These results could be attributed to the degree of crystallization. For the same Cr{sub 2}O{sub 3} content, the specimens that underwent a two-step heat treatment showed lower K values and higher Qf values than those heat-treated in one-step. These results could be attributed to the smaller crystallite size and higher degree of crystallization in the specimens obtained from the two-step heat treatment compared with those of the specimens heat-treated in one-step method.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Photoluminescence and cathodoluminescence properties of Eu{sup 3+} ions activated AMoO{sub 4} (A = Mg, Ca, Sr, Ba) phosphors

Highlights: • Under 393 nm excitation, strong red emission located at 615 nm was observed in all the samples. • The Eu{sup 3+}-activated CaMoO{sub 4} phosphor exhibited the strongest PL properties. • The CIE chromaticity coordinate of Eu{sup 3+}-activated CaMoO{sub 4} phosphor was (0.647,0.352). • The color purity of Eu{sup 3+}-activated CaMoO{sub 4} phosphor was 92.8%. • Strong CL properties were observed in the Eu{sup 3+}-activated CaMoO{sub 4} phosphor. - Abstract: Eu{sup 3+}-activated AMoO{sub 4} (A = Mg, Ca, Sr, Ba) phosphors were synthesized by a solid-state reaction method. Photoluminescence and cathodoluminescence (CL) spectra as well as X-ray diffraction patterns were measured to characterize the fabricated samples. Under 393 nm excitation, strong red emissions located at ∼615 nm corresponding to the {sup 5}D{sub 0} → {sup 7}F{sub 2} transition of Eu{sup 3+} ions were observed in all the samples. Compared with other Eu{sup 3+} ions activated AMoO{sub 4} (A = Mg, Sr, Ba) phosphors, Eu{sup 3+}-activated CaMoO{sub 4} phosphor exhibited the strongest red emission intensity with better Commission Internationale de L’Eclairage chromaticity coordinate and higher color purity. Furthermore, the CL results indicated that the Eu{sup 3+}-activated CaMoO{sub 4} phosphor had excellent luminescence properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Auto-combustion synthesis and characterization of Mg doped CuAlO{sub 2} nanoparticles

The synthesis of pure and Mg doped Copper aluminumoxide CuAlO{sub 2}nanoparticles, a promising p-type TCO (transparent conducting oxide) have been done bysol gel auto combustion method using NaOH as a fuel, calcinated at 600°C. The structural properties were examined by XRD and SEM techniques. The optical absorption spectra of CuAlO{sub 2} sample recorded by UV-VIS spectrophotometer in the range of 200 to 800 nm have been presented. The crystallite size was determined by powder X-ray diffraction technique. The electrical behavior of pure and Mg doped CuAlO{sub 2} has been studied over a wide range of frequencies by using complex impedance spectroscopy.The variation of a.c. conductivity has been studied as function of frequency and temperature. The data taken together conclude that doping causes decreases in the ac conductivity of the nanoparticles as compared with the pure nanoparticles. Mg doping affects the optical properties and band gap.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of Sm-Rich Phase on Corrosion Behavior of Hot-Extruded AZ31-1.5Sm Magnesium Alloy

The effects of Sm on the corrosion and microstructure behavior of hot-extruded AZ31 magnesium alloy were investigated by SEM, TEM, weight loss analysis, and electrochemical measurements. The results indicated that granular Al{sub 2}Sm phase ~ 4 μm in size in the hot-extruded AZ31 magnesium alloy modified with 1.5 wt.% Sm leads to significant grain refinement. The corrosion rate decreased from 15.98 × 10{sup −4} to 11.19 × 10{sup −4} g cm{sup −2} h{sup −1} in the transverse section and from 8.57 × 10{sup −4} to 6.20 × 10{sup −4} g cm{sup −2} h{sup −1} in the longitudinal section. Compared to the unmodified alloy, the corrosion potential of the Sm-modified alloy in the transverse and longitudinal sections increased by 98 and 62 mV, respectively, and the R{sub ct} value (charge transfer resistance) in the transverse and longitudinal sections of the modified alloy increased from 1764 and 1756 to 2928 and 2408 Ω cm{sup 2}, respectively. The results showed that the corrosion resistance of hot-extruded AZ31 magnesium alloy was significantly improved by Sm addition due to the grain refinement, the decreased dislocation density, and the suppression of micro-galvanic corrosion caused by Al-Sm-(Mn) intermetallic compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Texture Effect on Fatigue Crack Propagation Behavior in Annealed Sheets of an Al-Cu-Mg Alloy

The effects of texture, including Brass, Goss + Cube and Cube, on the fatigue crack growth behavior in annealed Al-Cu–Mg alloy sheets were characterized in this investigation. Results showed that the Goss + Cube sheet possessed the greatest fatigue threshold value and the lowest fatigue crack propagation (FCP) rate, and the Brass sheet presented the smallest threshold value and the greatest FCP rate among the three textured sheets. SEM results showed more slip bands and more tortuous crack path formed in Goss + Cube sheet during cyclic loading, and EBSD results showed that numerous dramatic crack deflections occurred when fatigue crack propagated across Goss-grain boundary in Goss + Cube sheet, indicating that the grain orientations including Goss and Cube had positive effect on enhancing the FCP resistance. On the one hand, Goss and Cube grains have more high Schmid factor slip systems than Brass grain, promoting persistent slip bands formation and externally applied energy consumption, consequently giving rise to a high resistance to FCP. On the other hand, Goss grains could induce crack deflection with large twist angles, resulting in more energy consumption during the cracking process and thereby enhance the FCP resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructural Characterization and Electrochemical Behavior of AA2014 Al-Cu-Mg-Si Alloy of Various Tempers

AA2014 Al-Cu-Mg-Si alloy is subjected to aging heat treatment, and microstructural features and electrochemical behavior of the AA2014 Al-Cu-Mg-Si alloy of various tempers have been characterized. Hardness measurement of the alloy of different tempers showed typical age hardening behavior. X-ray diffraction and transmission electron microscopy studies revealed the presence of characteristic phases. Differential scanning calorimetry study displayed the sequence of solid-state precipitation and dissolution reactions in the AA2014 alloy of various tempers. Electrochemical behavior was assessed by measurement of variation of open-circuit voltage with time, potentiodynamic polarization and potentiodynamic cyclic polarization of the AA2014 alloy of various tempers in 3.5 wt.% NaCl solution at near neural (pH ~ 7) and at alkaline (pH 12) conditions. Potentiodynamic polarization studies of different tempers in 3.5 wt.% NaCl solution at pH ~ 7 showed that the corrosion potential (E{sub corr}) value has shifted toward more negative (active) direction with increasing aging time. The cyclic polarization in 3.5 wt.% NaCl solution at pH ~ 7 displayed active–passive behavior and also showed a large hysteresis loop indicating high pit growth damage.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Microstructural, mechanical and electrochemical behaviour of a 7017 Al–Zn–Mg alloy of different tempers

The aim of the investigation is to assess the microstructural features and associated physical, mechanical and electrochemical properties of a 7017 Al–Zn–Mg alloy of various tempers. A 7017 Al–Zn–Mg alloy was subjected to different ageing schedules to produce under-(T4), peak-(T6), over-(T7) and highly over-aged tempers. Optical microscopy, hardness measurement, electrical conductivity measurement, tensile testing and SEM fractographs, differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and electrochemical polarization studies have been used to characterize the alloy tempers. Hardness measurement and tensile testing showed the characteristic age hardening phenomenon of aluminium alloys. Optical and TEM micrographs have revealed the variation in size of matrix strengthening η′ (MgZn{sub 2}) and also the size and distribution of grain boundary η (MgZn{sub 2}) precipitate with ageing time. DSC thermograms exhibiting exothermic and endothermic peaks indicated the characteristic solid state reaction sequence of the 7017 alloy. Potentiodynamic polarization study of the 7017 alloy of various tempers in 3.5 wt.% NaCl solution at near neutral pH showed typical active metal dissolution behaviour, but at pH 12 an active–passive–transpassive transition behaviour has been observed. - Graphical abstract: TEM micrograph of the 7017 aluminium alloy of various tempers (a, b) under aged (T4), (c, d) peak aged (T6), (e, f) over aged (T7) and (g, h) highly over-aged. Display Omitted - Highlights: • 7017 Al-Zn-Mg alloy was subjected to different artificial ageing treatments. • Characterization of 7017 alloy tempers by hardness, tensile, DSC, TEM and electrochemical behaviour. • Structure-properties relationship of the 7017 Al-Zn-Mg alloy of various tempers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Mechanical behavior and texture development of over-aged and solution treated Al-Cu-Mg alloy during multi-directional forging

The effects of initial heat treatments, i.e. solution treating and over ageing, on deformation behavior of an age hardenable Al-Cu-Mg alloy, including mechanical properties and texture evolution, during multi-directional forging (MDF) are investigated. Hardness measurements, electron back scatter diffraction (EBSD) maps, and differential scanning calorimetry (DSC) are carried out. Mechanical behaviors of the alloy in terms of compressive stress and hardness test after MDF are investigated. In both solution treated and over-aged alloys, the compressive stress during MDF shows an increase up to the second pass, and by further straining the flow stress is decreased. However, shear and deformation bands are formed in both solution treated and over-aged alloys, the density of these instabilities in the solution treated alloy is higher than that in over-aged alloy. In the solution treated alloy, not only large particles induce deformation bands, but also the dynamically formed GPB zones/Cu-Mg co-clusters. Texture analysis shows that the shear component of C {001}<110> (Φ{sub 1} = 90°, Φ = 0°, Φ{sub 2} = 45°) is developed with 18 mrd during MDF of the over-aged alloy. In the solution treated alloy, due to the high density of deformation bands and different microchemistry of the matrix in comparison with that of the over-aged alloy, the Copper type texture component {112}<111> (Φ{sub 1} = 90°, Φ = 35°, Φ{sub 2} = 45°) is developed with 11 mrd.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of heat treatment variables on the formation of precipitate free zones (PFZs) in Mg-8Al-0.5Zn alloy

Highlights: • The effect of heat treatment variables on the development of PFZs in the AZ80 Mg alloy has been systematically examined. • PFZ width is found to be strongly dependant on aging temperature as compared to aging time. • The PFZ width in the AZ80 alloy is found to be weakly dependant on the solution temperature and quenching rate. • The solute depletion is found to be the dominant factor in explaining the evolution of PFZ width. - Abstract: The present study is focussed on investigating the effect of heat treatment variables on the formation of precipitate free zones (PFZs) in the AZ80 Mg alloy. The effect of solutionizing temperature, quenching media, aging temperature and time on the PFZ development has been systematically examined. Scanning electron microscopy and nanoindentation were employed to characterize the PFZ regions. Electron probe micro analysis (EPMA) was used to examine the role of solute depletion in the formation of these zones. Moreover, the estimation of vacancy concentration profiles near the grain boundary was used to investigate the role of vacancy depletion. The solute depletion is found to be the dominant mechanism in the development of PFZ regions as compared to vacancy.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Characterization of hot extrusion and heat treatment on mechanical properties in a spray formed ultra-high strength Al-Zn-Mg-Cu alloy

Highlights: • The spray forming technology was used to fabricate ultra-high strength aluminum alloy. • The alloy under RRA state obtained the highest ultimate tensile strength of 732 MPa. • The effects of dislocations, solutes and precipitates etc., on yield strength were calculated. • Precipitation was characterized as the main strengthening mechanism for aging states. - Abstract: To obtain the optimal mechanical properties, several processes including spray forming technology, two passes hot extrusion and substantial heating treatments were operated on an Al-Zn-Mg-Cu-Zr alloy. The characterization methods used in this study include tensile tests, X-ray diffraction, differential scanning calorimetry and microstructure observations by optical microscope, scanning and transmission electron microscopy. The typical characteristics were the refined grain, homogeneous precipitates and porosity in the as-deposited pre-forms. The ultimate tensile strength, yield strength, hardness and elongation improved significantly after two passes hot extrusion. A good combination of ultimate tensile strength at 704 MPa and elongation at 9.7% were achieved under peak-aged treatment. The best ultimate tensile strength was obtained at 732 MPa after re-aging and regression. It was main dimple fracture in the extruded and aging treated specimens while brittle fracture for the as-deposited. The secondary phases were main MgZn{sub 2} and Al{sub 3}Zr dispersoids throughout all the states. The contributions of grain boundaries, dislocations, solid-solution and precipitates on the yield strength were analyzed using a quantitative equation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Lattice rotations in precipitate free zones in an Al-Mg-Si alloy

Highlights: • Recovery processes in precipitate free zones differ from those in grain interiors. • Most precipitate free zones contain few dislocations, after deformation. • Deformation can induce large misorientations in precipitate free zones. • Some deformed precipitate free zones contain nanoscale grains. - Abstract: Scanning precession electron diffraction and automated crystal orientation mapping in a transmission electron microscope (TEM) have been applied to quantitatively study the crystal orientation of precipitate free zones (PFZs) of four GB regions in an AA6060 alloy in peak aged condition (temper T6) after uniaxial compression to 20% engineering strain. The PFZ width in the alloy was found to be w = 170 ± 40 nm. The results show that some PFZs develop significant misorientations relative to their parent grain, and represent, to the best knowledge of the authors, the first quantitative evidence of this. This misorientation may either be constant inside a particular PFZ, making it appear like a band or a very elongated subgrain, or be partitioned in discrete regions with a diameter comparable to the PFZ width, making the former PFZ into a collection of small grains. The band-like PFZ observed in this work had a misorientation relative to its parent grain of ≈ 7°, while the grain-like PFZ had grains with misorientations between ≈ 12° and ≈ 20° relative to its parent grain. The other PFZs that were observed had only limited misorientations relative to their parent grains, and had either dislocations perpendicular to the GB plane or a dislocation wall at the transition region. A general TEM study of the material at various engineering strains was also conducted and suggests that grain-like PFZs are more frequent for larger strains, indicating that the different PFZ features are likely due to different strain localisation in individual PFZs. This localisation is expected to be influenced by the orientation of the loading axis relative to crystal orientations and GB planes. It is also suggested that the different PFZ features engender different work hardening rates and possibly affect nucleation of intergranular fracture. The results support previous studies on the microstructure evolution of PFZs in age-hardenable aluminium alloys during deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A comparative research on bobbin tool and conventional friction stir welding of Al-Mg-Si alloy plates

Highlights: • 6061-T4 Al plates were successfully welded by both BT-FSW and C-FSW processes. • A wide welding parameter window was achieved with bobbin tool. • BT-FSW joints showed good strength similar to that of C-FSW joints. • Proving that an Isothermal Dissolution Layer Theory also apply to BT-FSW - Abstract: In our work, Al-Mg-Si (6061Al -T4) plates of 6 mm thickness were subjected to bobbin tool friction stir welding (BT-FSW) and conventional friction stir welding (C-FSW) for comparison. How the welding process affects the microstructure and mechanical properties was investigated at various rotation rates and welding speeds. The results showed that butt FSW joints with high quality could be produced at the selected parameters. The joint strength rose with enhanced welding speed and was nearly independent of the rotation rate in both the welding processes. The strength of the joints produced with BT-FSW reached the same level as that of the C-FSW. The maximum joint strength of 229 MPa was 93% of the base material (BM), which is superior to the reported results of 60–80% for the T4 condition. The fracture position of most of the joints was in the heat-affected zone (HAZ), which is the lowest hardness zone.

36 MATERIALS SCIENCE↗