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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Welded and Hydrogen Charged Zircaloy-4 and Welded Stainless Steel 347 Property Data and Microstructures for the Target Solution Vessel and Support Lines of SHINE

SHINE Medical Technologies is developing a facility that will produce molybdenum-99 for medical isotope procedures. As part of this facility, a metal tank, called the target solution vessel (TSV), will hold a uranyl sulfite solution. The TSV must withstand neutron irradiation near room temperature and potential corrosion from the aqueous solution. The large cylindrical TSV will be fabricated by welding and will have numerous pipes and connections also attached via welding. The vessel and those pipes will have varying thicknesses so both gas tungsten arc welding (GTAW) and flux-cored arc welding (FCAW) will be necessary to fabricate different sections. The original material under consideration for the TSV was Zircaloy-4 (Zry-4), but it is known to form a hydride which can degrade its mechanical properties. Thus, some investigation here is focused on the effects of hydrogen uptake in the Zry-4. Additionally, the alternative material being considered is AISI 347, a stainless steel. Both materials have little existing data for their neutron irradiation behavior below 100°C, and both have open questions on the weld behavior under neutron irradiation. Testing has focused on characterizing their weld properties with tensile tests and performing neutron irradiation of samples in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL).

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2020

Second Annual Progress Report on Correlation Between Microstructure and Mechanical Properties of Neutron-Irradiated Ferritic-Martensitic and Austenitic Steels

Ferritic-martensitic steels G92-2b (an optimized Grade 92 heat), NF616 and T91, and austenitic stainless steel 800H and its Grain Boundary Engineering (GBE)-treated version 800H-TMP (ThermoMechanical Processing) were irradiated in the High Flux Isotope Reactor (HFIR) of Oak Ridge National Laboratory (ORNL) and the Advanced Test Reactor (ATR) of Idaho National Laboratory (INL). Selected G92-2b samples were irradiated up to 14.66 dpa in the HFIR at two temperature ranges: 400–496.7°C and 683.3– 720°C. NF616 and T91 were irradiated in the ATR up to 8.16 dpa with the irradiation temperatures ranged from 241°C to 447.5°C. Alloy 800H and 800H-TMP samples were irradiated in both the HFIR and the ATR. Selected 800H and 800H-TMP samples had HFIR irradiation to 1.28 dpa at 580°C and ATR irradiation up to 9.12 dpa at 359°C to 431°C. Vickers hardness measurements, fractography, and microstructural characterization were performed on the selected samples in the Low Activation Materials Design and Analysis (LAMDA) laboratory. Radiation-hardening of G92-2b was observed at the lower doses and lower irradiation temperatures (400- 496.7°C), with GB03 (0.52 dpa at 400°C) and GB04 (7.44 dpa at ~490°C) showing ~12% and ~8% hardening, respectively. Softening by ~14% was observed for GB05 (14.66 dpa at 496.7°C). Radiationsoftening of G92-2b was more prevalent at the higher irradiation temperatures (683.3-~720°C), with GB10 (0.46 dpa at 683.3°C), GB11 (7.44 dpa at ~720°C), and GB12 (14.63 dpa at ~720°C) showing ~8%, ~8%, and ~40% softening, respectively. Radiation-hardening of NF616 and T91 was observed with the hardness increased by ~37% to ~65% depending on the irradiation doses and irradiation temperatures. Within the studied irradiation conditions of NF616 and T91, samples with a higher dose had a larger hardness after irradiation. All the tested alloy 800H and 800H-TMP samples in this work showed radiation-hardening by ~96±7% to ~152±10%. Alloy 800H-TMP tended to have slightly smaller radiation-hardening than alloy 800H. The fractography results of G92-2b sample GB03, GB10, and GB11, together with the previously characterized fractography of GB04, GB05, and GB12, indicated that the ductility of G92-2b was maintained up to 14.66 dpa at the lower irradiation temperatures of 400-496.7°C, while some loss of ductility (less necking) was observed for higher doses at the higher irradiation temperatures of 683.3-720°C. This agrees with the previously reported tensile test results of G92-2b, where the elongation of G92-2b was reduced at higher doses at the higher irradiation temperatures. Dimple sizes increased at higher doses, which are more evident at the higher irradiation temperatures of 683.3-~720°C. The fractography of NF616 sample D2 (2.96 dpa at 291.5°C), D4 (5.91 dpa at 359°C), and D6 (8.16 dpa at 431°C) indicated loss of ductility with negligible necking for sample D2, while ductile failure for samples D4 and D6. Fractography of alloy 800H and 800H-TMP samples in various irradiation conditions showed ductile failure with obvious necking. Dimples were observed, with some of them containing large Ti-rich particles, in all the 800H/800H-TMP samples. Electron backscatter diffraction characterization of GB12 indicated the recovery of the lath structure, which was generally replaced by an equiaxed grain structure. Transmission electron microscopy (TEM) characterization showed the presence of frequent M 23 C 6 (M = primarily Cr), MX (M = primarily V), spherical Nb(C,N) precipitates, and occasional Laves phase precipitates in the G92-2b samples. MX precipitates with sizes of 20-30 nm were observed at boundaries of smaller grains, indicating the pinning effect of the V-rich precipitates. The lath structure recovery was more evident at the higher irradiation temperatures (683.3-~720°C), with decreased densities of line dislocations and M23C6 precipitates. The irradiated T91 (TA04) showed the growth of M23C6 precipitates to 101 ± 40 nm from the initial 68 ± 22 nm in the unirradiated condition. Dislocation loops of both {100} and {111} types were present in TA04. TEM characterization was also performed on the irradiated 800H (N4, N5, N6, and AR2) and 800H-TMP (P4, P5, P6, and HG1). Accumulation of M 23 C 6 precipitates at grain boundaries was observed in all the xii 800H/800H-TMP samples, and the presence of Ti(C,N) precipitates at grain boundaries and in the matrix was observed in the irradiated 800H-TMP. Some Ti(C,N) precipitates are embedded in the M 23 C 6 precipitates, maintaining specific orientation relationships between the precipitates and between the precipitate and matrix. In addition, nanoscale Si-rich clusters were observed in the matrix of all the 800H/800H-TMP samples, with EDS Si maps tending to have a lower contrast in 800H-TMP samples. Atom probe tomography was conducted on the same samples, supported by a Rapid Turnaround Examination project under Nuclear Science User Facilities. The results are being analyzed to be integrated with the TEM results for a confident description of the γ’ precipitates. Dislocation loops also formed in all the 800H/800H-TMP samples. The density and the average size of dislocation loops were quantified to be in the order of 10 22 – 10 23 m -3 and 11.7 – 15.9 nm, respectively, in the ATR-irradiated 800H/800H-TMP samples. The loop densities in irradiated 800H were higher than that in irradiated 800H-TMP under the same irradiation conditions. Further systematic data analyses, together with some complementary experiments, will be pursued for these samples to foster peer-reviewed journal article publications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Characterization of paste microstructure for durability properties of concrete

In this study, paste samples from different cementitious systems were characterized by using X-Ray Micro Computed Tomography (µ-CT) and Fluorescence Microscopy techniques. Quantitative and qualitative aspects of defects from paste samples were investigated to develop indicators of durability related properties of corresponding concrete samples. In the first phase of this study, hour glass shaped 3D printed molds were used to investigate five cementitious combinations consisting of three cement types (Coarse Ground portland cement, Type IL Portland Limestone Cement and Type I/II ordinary portland cement) and fly ash as a supplementary cementitious material. In the second phase, metal molds were used to compare the results of Coarse Ground portland cement with Type I ordinary portland cement, 5% of which was replaced with colloidal nanosilica. Potential correlations between paste and concrete have been presented. This work was supported by US Department of Energy and North Dakota Department of Commerce.

36 MATERIALS SCIENCE↗
DOE OSTI2017

The effect of Si on the microstructure and mechanical properties of spark plasma sintered boron carbide

Highlights: • Si addition leads to a dense final product at a low sintering temperature. • The added Si preferentially formed SiC and borosilicate glass instead of replacing the chain atoms in boron carbide. • The hardness of our Si-containing boron carbide is 30–35% greater than currently in-use commercial boron carbide plates. - Abstract: Fully dense boron carbide discs were achieved by spark plasma sintering boron carbide powders with 10 wt% silicon. The silicon did not diffuse into boron carbide grains to produce a solid solution of Si-doped boron carbide; instead the silicon reacted with impurities in the starting powder to form β-SiC and borosilicate glass. The resultant new phases facilitated densification of the multiphase ceramic through liquid phase-assisted sintering. The resultant material exhibits improved hardness (34.3 GPa Vikers hardness under 1 kg load) with toughness comparable to both Si-free and commercially available boron carbide.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Reel-to-Reel Heat Treatment, Microstructure, and Superconducting Properties of Jelly-Roll Nb{sub 3}Al Superconducting Wire

In this work, we utilized the jelly-roll method to make a single-filament Nb{sub 3}Al precursor long wire, combining with a homemade reel-to-reel rapid heating and quenching (RHQ) equipment, and consequently the high-performance Nb{sub 3}Al superconducting wires had been prepared. By investigating the heating current and wire moving speed, the optimized RHQ heat treatment conditions of this Nb{sub 3}Al wire were obtained. The results suggest that the T{sub c} for the Nb{sub 3}Al superconducting wire is up to 17.4 K and the non-Cu critical current density (non-Cu J{sub c}) reaches 1238 A/mm{sup 2} at 4.2 K and 12 T, which indicates the bcc-phase Nb–Al supersaturated solid solution has already been generated. Considering the Nb{sub 3}Al precursor wire with a large thickness of Al layer, about 690 nm, such high J{sub c} is quite unexpected. The SEM analysis presents that there is still some unreacted Nb and Nb{sub 2}Al phase in the superconducting wire, which may result from the inhomogeneity of Nb and Al foils. This work implies the Nb{sub 3}Al superconducting wire is promising to the application of high-field superconducting magnets.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Influencing mechanism of Al-containing Zn coating on interfacial microstructure and mechanical properties of friction stir spot welded Mg–steel joint

Highlights: • Al-containing Zn coating improved Mg–steel interfacial wettability during friction stir spot welding (FSSW). • Pre-existing Al{sub 5}Fe{sub 2} phase in coating on steel surface promoted Mg–steel metallurgical bonding. • A high tensile-shear load of 4.3 kN was obtained in FSSW AZ31–steel joint. - Abstract: 2.4 mm thick AZ31 Mg alloy sheet and 1.5 mm Q234 steel sheet with a hot-dipped Al-containing Zn coating were friction stir spot welded (FSSW) using a pinless tool. It was shown that the Al-containing Zn coating played a crucial role in joining the Mg alloy and steel during FSSW. The Zn coating observably improved the Mg–steel interfacial wettability during FSSW, and the Al{sub 5}Fe{sub 2} phase in the Zn coating on the steel substrate surface promoted the metallurgical bonding of Mg alloy and steel. It was confirmed that the Al{sub 5}Fe{sub 2} phase on the steel surface resulted from the reaction between the steel substrate and the Al in the Zn coating during hot-dipping, and was not related to the Al-containing Mg alloy substrate. The tensile-shear load of the FSSW Mg–steel joint reached 4.3 kN. The fracture of the joint occurred along the interface on the steel substrate side. The interface between the Al{sub 5}Fe{sub 2} layer and Mg alloy substrate was the weakest region of the Mg–steel joint.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Mechanical properties, deformation behavior and microstructure evolution of Ti-43Al-6Nb-1Mo-1Cr alloys

Highlights: • The alloys exhibit excellent high-temperature tensile properties. • Activation energy of deformation (Q) and n are 571 KJ/mol and 2.765, respectively. • The hot processing maps of strain 0.5 and 0.6 are displayed. • Phase transformations and microstructure evolution are explained in different conditions. • Three types of deformation mechanisms are exhibited at different temperature. - Abstract: The high-temperature properties, microstructure evolution and deformation behavior of a novel Ti-43Al-6Nb-1Mo-1Cr(at.%) alloy were studied in this paper. The ultimate tensile strength (UTS) and elongation (δ) were tested at 800, 850, and 900 °C, in which the excellent strength 551 MPa, 510 MPa, and 382 MPa, and elongation 2.9%, 12.7%, and 16.8% were exhibited, respectively. Isothermal compression tests were carried out in the temperature range of 1100–1250 °C and strain rate range of 0.001–1.0 s{sup − 1}. Based on dynamic materials model (DMM) and phase diagram, dynamic recrystallization mechanism and phase transformation during thermal deformation were clarified and the hot processing maps were calculated. The experimental results show that the values of stress exponent (n) and the apparent deformation activation energy (Q) of Ti-43Al-6Nb-1Mo-1Cr(at.%) were calculated to be 2.77 and 571 KJ/mol. Meanwhile, three various types of microstructure evolution in different deformation conditions were discussed and concluded.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure and Mechanical Properties of Friction Stir Process Derived Al-TiO{sub 2} Nanocomposite

Aluminum-based composites have many advantages over their conventional counterparts. A major problem in such composites is the clustering of particles in the matrix. Friction stir processing (FSP) can homogenize particle distribution in aluminum-based composites. In this study, unannealed TiO{sub 2} particles were used to prepare Al-TiO{sub 2} nanocomposite using FSP. The TiO{sub 2} particles, about 1 µm, were dispersed into an aluminum matrix by 6 passes of FSP. The TiO{sub 2} particles were fractured by multiple FSP passes, leading to a nano-size particle distribution in the matrix. Nanoscale dispersion was confirmed by scanning electron microscopy and transmission electron microscopy. The fractured TiO{sub 2} particles reacted with the aluminum matrix to form Al{sub 3}Ti intermetallic and Al{sub 2}O{sub 3} ceramic. The progression of the Al-TiO{sub 2} reaction from the fourth to the sixth pass of FSP was revealed by x-ray diffraction. Due to the nanoscale dispersion, the yield and ultimate tensile strength of the composite increased to 97 and 145 MPa, respectively. Ductility of the composite decreased marginally compared to the as-received aluminum. As the dispersed particles pin dislocations, the strain-hardening rate of the composite was considerably increased and the same was seen in the Kocks-Mecking plot. The TiO{sub 2} particles are mechanically activated due to their fracture during FSP, hence leading to reaction with the matrix. The particle refinement and dispersion lead to a homogeneous matrix with higher strength.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Selective laser melting of 304L stainless steel: Role of volumetric energy density on the microstructure, texture and mechanical properties

The role of volumetric energy density on the microstructural evolution, texture and mechanical properties of 304L stainless steel parts additively manufactured via selective laser melting process is investigated. 304L is chosen because it is a potential candidate to be used as a matrix in a metal matrix composite with nanoparticles dispersion for energy and high temperature applications. The highest relative density of 99 %±0.5 was achieved using a volumetric energy density of 1400 J/mm 3 . Both XRD analysis and Scheil simulation revealed the presence of a small trace of the delta ferrite phase, due to rapid solidification within the austenitic matrix of 304L. Here, a fine cellular substructure ranged between 0.4–1.8 μm, was detected across different energy density values. At the highest energy density value, a strong texture in the direction of [100] was identified. At lower energy density values, multicomponent texture was found due to high nucleation rate and the existing defects. Yield strength, ultimate tensile strength, and microhardness of samples with a relative density of 99 % were measured to be 540 ± 15 MPa, 660 ± 20 MPa and 254 ± 7 HV, respectively and higher than mechanical properties of conventionally manufactured 304L stainless steel. Heat treatment of the laser melted 304L at 1200 °C for 2 h, resulted in the nucleation of recrystallized equiaxed grains followed by a decrease in microhardness value from 233 ± 3 HV to 208 ± 8 HV due to disappearance of cellular substructure.

304L stainless steel↗
NASA NTRS2016

Microstructural and Creep Properties of Boron- and Zirconium-Containing Cobalt-Based Superalloys

The effects of micro-additions of boron and zirconium on grain-boundary (GB) structure and strength inpolycrystalline γ(f.c.c.) plus γ’(L12) strengthened Co-9.5Al-7.5W-X at. % alloys (X=0-Ternary, 0.05B, 0.01B,0.05Zr, and 0.005B-0.05Zr at. %) are studied. Creep tests performed at 850 °C demonstrate that GB strength and cohesion limit the creep resistance and ductility of the ternary B- and Zr-free alloy due to intergranular fracture. Alloys with 0.05B and 0.005B-0.05Zr both exhibit improved creep strength due to enhanced GB cohesion,compared to the baseline ternary Co-9.5Al-7.5W alloy, but alloys containing 0.01B or 0.05Zr additions displayed no benefit. Atom-probe tomography (APT) is utilized to measure GB segregation, where B and Zr are demonstrated to segregate at GBs. A Gibbsian interfacial excess of 5.57 ± 1.04 atoms nm(exp) -2 was found for B at aGB in the 0.01B alloy and 2.88 ± 0.81 and 2.40 ± 0.84 atoms nm2 for B and Zr, respectively, for the 0.005B-0.05Zr alloy. The GBs in the highest B-containing (0.05B) alloy exhibit micrometer-sized boride precipitates with adjacent precipitate denuded-zones (PDZs), whereas secondary precipitation at the GBs is absent in theother four alloys. The 0.05B alloy has the smallest room temperature yield strength, by 6%, which is attributedto the PDZs, but it exhibits the largest increase in creep strength (with an ~2.5 order of magnitude decrease inthe minimum strain rate for a given stress at 850 °C) over the baseline Co-9.5Al-7.5W alloy.

Creep↗
DOE OSTI2018

Microstructure and mechanical properties of intragranular W-Cu/TiC-ZrC composite prepared by reactive melt infiltration at 1300 °C

Highlights: • W-Cu/TiC-ZrC composites with nano W dispersoids were prepared by reactive melt infiltration. • The nano-sized dispersoids were analyzed by TEM in detail. • The intragranular nano W dispersoids and ribbon like precipitates have toughening effects. - Abstract: Newly intragranular W-Cu/TiC-ZrC composites with nano W dispersoids in TiC matrix have been prepared by reactive melt infiltration at 1300 °C for 1 h in vacuum using molten Zr-Cu binary alloys and a (Ti{sub 0.75},W{sub 0.25})C solid solution powder as raw materials. The as-synthesized composites consist of major phases of W, Cu, TiC and ZrC. With the decrease of Zr content from 66 to 21 at.% in the Zr-Cu infiltrator, the reaction formed W phase in the composite has changed from micron-sized intergranular grains to nano-sized rounded inclusions in TiC{sub y} grains. The crystallographic orientation relationship at W and TiC interfaces are detected as:(0 1 1-bar ){sub W}//(1 1 1-bar ){sub TiC}&[0 1 1]{sub W}//[0 1 1]{sub TiC} and (4 1 1){sub W}//(4 2 4){sub TiC}&[0 1 1-bar ]{sub W}//[4 2-bar 3-bar ]{sub TiC}. Nano-sized lamellar structure with both W and Cu rich is detected to have super-lattice structure based on the TiC lattice. The elastic modulus, flexural strength, fracture toughness of the intragranular W-Cu/TiC-ZrC composite infiltrated with Zr{sub 14}Cu{sub 51} melt are 207.5 GPa, 457 MPa and 10.21 MPa∙m{sup 1/2}, respectively. The intragranular nano W dispersoids and ribbon like precipitates hinder crack propagation via crack deflection and bridging.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Advanced Process Possibilities in Friction Crush Welding of Aluminum, Steel, and Copper by Using an Additional Wire

Joining sheet metal can be problematic using traditional friction welding techniques. Friction crush welding (FCW) offers a high speed process which requires a simple edge preparation and can be applied to out-of-plane geometries. In this work, an implementation of FCW was employed using an additional wire to weld sheets of EN AW5754 H22, DC01, and Cu-DHP. The joint is formed by bringing together two sheet metal parts, introducing a wire into the weld zone and employing a rotating disk which is subject to an external force. The requirements of the welding preparation and the fundamental process variables are shown. Thermal measurements were taken which give evidence about the maximum temperature in the welding center and the temperature in the periphery of the sheet metals being joined. The high welding speed along with a relatively low heat input results in a minimal distortion of the sheet metal and marginal metallurgical changes in the parent material. In the steel specimens, this FCW implementation produces a fine grain microstructure, enhancing mechanical properties in the region of the weld. Aluminum and copper produced mean bond strengths of 77 and 69 pct to that of the parent material, respectively, whilst the steel demonstrated a strength of 98 pct. Using a wire offers the opportunity to use a higher-alloyed additional material and to precisely adjust the additional material volume appropriate for a given material alignment and thickness.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Microstructures and Microhardness Properties of CMSX-4{sup ®} Additively Fabricated Through Scanning Laser Epitaxy (SLE)

Epitaxial CMSX-4{sup ®} deposition is achieved on CMSX-4{sup ®} substrates through the scanning laser epitaxy (SLE) process. A thorough analysis is performed using various advanced material characterization techniques, namely high-resolution optical microscopy, scanning electron microscopy, energy-dispersive x-ray spectroscopy, x-ray diffraction, and Vickers microhardness measurements, to characterize and compare the quality of the SLE-fabricated CMSX-4{sup ®} deposits to the CMSX-4{sup ®} substrates. The results show that the CMSX-4{sup ®} deposits have smaller primary dendritic arm spacing, finer γ/γ′ size, weaker elemental segregation, and higher microhardness compared to the investment cast CMSX-4{sup ®} substrates. The results presented here demonstrate that CMSX-4{sup ®} is an attractive material for laser-based AM processing and, therefore, can be used in the fabrication of gas turbine hot-section components through AM processing.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructural Evolution and Mechanical Properties of Ti-22Al-25Nb (At.%) Orthorhombic Alloy with Three Typical Microstructures

Microstructural evolution, tensile and creep behavior of Ti-22Al-25Nb (at.%) orthorhombic alloy with three typical microstructures were investigated. The three typical microstructures were obtained by different solution and age treatment temperatures and analyzed by the BSE technique. The tensile strengths of the alloy at room temperature and 650 °C were investigated. The creep behaviors of the three typical microstructures were also studied at 650 °C/150 MPa for 100 h in air. The phase transformation mechanisms in creep deformation were also found. The experimental results showed that the formations of the three typical microstructures were decided by the isothermal forging and heat treatment. It was supposed that the high-temperature solution treatment might be dominant for the volume fraction and diameter of the equiaxed particles. While the double age treatment would lead to lamellar O phases. Due to grain refinement strengthening, the equiaxed microstructure presented the best tensile strength and ductility. The fully lamellar microstructure had the best creep resistance than that of other microstructures. In this paper, the phenomenon of creep-induced α{sub 2} phase decomposition was occurred during creep deformation of the equiaxed microstructure.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Stress Wave Attenuation in Aluminum Alloy and Mild Steel Specimens Under SHPB Tensile Testing

Investigations on the effect of intensity of incident pressure wave applied through the striker bar on the specimen force histories and stress wave attenuation during split Hopkinson pressure bar (SHPB) tensile testing are presented. Details of the tensile SHPB along with Lagrangian x–t diagram of the setup are included. Studies were carried out on aluminum alloy 7075 T651 and IS 2062 mild steel. While testing specimens using the tensile SHPB setup, it was observed that the force calculated from the transmitter bar strain gauge was smaller than the force obtained from the incident bar strain gauge. This mismatch between the forces in the incident bar and the transmitter bar is explained on the basis of stress wave attenuation in the specimens. A methodology to obtain force histories using the strain gauges on the specimen during SHPB tensile testing is also presented. Further, scanning electron microscope images and photomicrographs are given. Correlation between the microstructure and mechanical properties is explained. Further, uncertainty analysis was conducted to ascertain the accuracy of the results.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Fiber Laser Welding–Brazing Characteristics of Dissimilar Metals AZ31B Mg Alloys to Copper with Mg-Based Filler

Fiber laser welding–brazing of 1-mm-thick AZ31B Mg alloys to 1.5-mm-thick copper (T2) with Mg-based filler was performed in a lap configuration. The weld appearance, interfacial microstructure and mechanical properties were investigated with different heat inputs. The results indicated that processing windows for optimizing appropriate welding parameters were relatively narrow in this case. Visually acceptable joints with certain strength were achieved at appropriate welding parameters. The maximum tensile-shear fracture load of laser-welded-brazed Mg/Cu joint could reach 1730 N at the laser power of 1200 W, representing 64.1% joint efficiency relative to AZ31Mg base metal. The eutectic structure (α-Mg + Mg{sub 2}Cu) and Mg-Cu intermetallic compound was observed at the Mg/Cu interface, and Mg-Al-Cu ternary intermetallic compound were identified between intermetallics and eutectic structure at high heat input. All the joints fractured at the Mg-Cu interface. However, the fracture mode was found to differ. For laser power of 1200 W, the surface was characterized by tearing edge, while that with poor joint strength was almost dominated by smooth surface or flat tear pattern.

36 MATERIALS SCIENCE↗