Explore the vast range of titles available.

To solve the problems of poor weld formation, difficult slag removal, and inferior joint microstructure and hardness in conventional narrow-gap submerged arc welding (NG-SAW), a swing arc NG-SAW process assisted by pre-embedding cold wires was proposed. Synergistically optimizing the welding energy parameters and additional cold wires ensured sound weld formation and enhanced slag detachability, while the efficiency of multilayer welding was improved by reducing the number of weld layers by 33.3%. The slag adhesion mechanism is clarified as follows: a high welding heat input facilitates elemental diffusion at the weld–slag interface, leading to the formation of a continuous and thick interlayer composed of (Fe,Mn)O and MgO-Al2O3-CaO phases. This interlayer strengthens the chemical bonding between slag and weld, thereby impeding slag removal. Microstructure evolution analysis of the multilayer welded joint revealed that the variable-angle design increases the groove volume and, combined with the heat-absorbing effect of the additional wires, accelerates molten pool cooling, thereby refining grains in both the weld metal zone and reheat-affected zone. Meanwhile, the tempering exerted by the heat-affected zone (HAZ) of the subsequent weld layer on the previous layer is attenuated. This promotes the gradual transformation of hard-brittle lath martensite in the coarse-grained heat-affected zone (CGHAZ) of the bottom layer into tougher tempered martensite/bainite in the CGHAZ of the upper layers. As a result, the hardness uniformity within the HAZ, the critical weak region of the joint, was enhanced by 54%, enabling synchronous improvement in microstructural homogeneity, hardness distribution, and overall welding efficiency.

Pulsed laser welding of TC4 titanium alloy to SUS301L stainless steel with copper sheet as interlayer was studied in this paper. Microstructures of the joints were analyzed by optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The mechanical properties of the joints were measured by nano-indentation test and tension test. Experimental results showed that copper interlayer was helping to decrease the Ti–Fe intermetallics by forming Cu solid solution, Cu 2 Ti, Cu–Ti, and Cu–Ti 2 in the weld. The composition and microstructure in the weld were uneven, which led to an inhomogeneous distribution of the hardness. The average tensile strength of the joint was 350 MPa, and all the tensile samples fractured in the Cu–Ti 2 layer with a maximum hardness in the weld adjacent to TC4 titanium alloy side.

The paper deals with an investigation of the influence of tool shape and weld configuration on the microstructure and mechanical properties of Al 6082 alloy FSW joints. Three types of tool with different probe shapes and shoulder surfaces and two weld configurations (onesided and two-sided) were used in experiments. It was shown that all tool types produce high quality butt joints free from defects or imperfections. The best tensile performance was obtained for FSW joints produced by a conventional and Triflute tool. The results obtained for joints produced by a simple unthreaded probe without grooves and with a flat shoulder are significantly lower. The joint configuration influenced mechanical properties - the two-sided welds exhibited lower mechanical properties due to greater heat transference into the material during the second pass. The changes in mechanical properties reflected changes in weld microstructure, in particular, the softening of the weld nugget was associated with intense dynamic recovery producing grains that were nearly free of dislocations. A hypothesis explaining the well-known differences in microstructure between the advancing and retreating sides is also advanced. The differences were predicted based on a recently elaborated coupled thermal/flow model developed for FSW joints.

In this study, to meet the development and application requirements for high-strength and high-toughness energetic structural materials, a representative volume element of a TA15 matrix embedded with a TaZrNb sphere was designed and fabricated via diffusion bonding. The mechanisms of the microstructural evolution of the TaZrNb/TA15 interface were investigated via SEM, EBSD, EDS, and XRD. Interface mechanical property tests and in-situ tensile tests were conducted on the sphere-containing structure, and an equivalent tensile-strength model was established for the structure. The results revealed that the TA15 titanium alloy and joint had high density and no pores or cracks. The thickness of the planar joint was approximately 50–60 μm. The average tensile and shear strengths were 767 MPa and 608 MPa, respectively. The thickness of the spherical joint was approximately 60 μm. The Zr and Nb elements in the joint diffused uniformly and formed strong bonds with Ti without forming intermetallic compounds. The interface exhibited submicron grain refinement and a concave–convex interlocking structure. The tensile fracture surface primarily exhibited intergranular fracture combined with some transgranular fracture, which constituted a quasi-brittle fracture mode. The shear fracture surface exhibited brittle fracture with regular arrangements of furrows. Internal fracture occurred along the spherical interface, as revealed by advanced in-situ X-ray microcomputed tomography. The experimental results agreed well with the theoretical predictions, indicating that the high-strength interface contributes to the overall strength and toughness of the sphere-containing structure. [Display omitted] •High-strength mechanical properties of the interface of the TA15/TaZrNb MEA composite fabricated via diffusion bonding.•Investigation on the fracture mechanisms of the RVE embedded with a sphere by in-situ μCT tensile tests.•A tensile-strength equivalent model for the RVE embedded with a sphere is established.•The concave–convex interlocking structure at the interface plays a crucial role in resisting failure.

In this study, fiber laser butt welding was performed on a 6 mm thick Ti-6Al-3Nb-2Zr-1Mo alloy and 10CrNi3MoV steel using two interlayer configurations, with the innovative introduction of an external alternating magnetic field. The microstructure, element distribution, and mechanical properties of the welded joint were investigated through various methods including scanning electron microscopy, energy-dispersive X-ray spectrometer, and X-ray diffraction. Results showed that joints with two interlayer configurations were present in an interfacial layer with non-uniform thickness and poor mechanical properties, due to the heterogeneous heat distribution in the thickness direction and the mixing of elements during the laser welding process. Applying an alternating magnetic field facilitated convection of the molten pool from center to sides, which accelerated forced convection in both vertical and horizontal directions leading to more uniform heat distribution as well as element distribution resulting in a significant reduction or disappearance of unmelted Cu for different interlayers, while also reducing the thickness of the interfacial layer at the upper part of the joint and significantly improving tensile strength by 5.9% and 8.3%, respectively.

Chip to chip bonding techniques using Cu bumps capped with thin solder layers have been frequently applied to 3D chip stacking technology. We studied the effect of joint microstructure on shear strength. Joints were formed by joining Sn/Cu bumps on a Si die and Sn/Cu layers on another Si die at 245–330°C using a thermo-compression bonder. Three different types of microstructures were fabricated in the joints by controlling the bonding temperature and time, (1) a Sn-rich phase with a Cu 6 Sn 5 phase at the Cu interfaces, (2) a Cu 6 Sn 5 phase in the interior with a Cu 3 Sn phase at the Cu interfaces, and (3) one single Cu 3 Sn phase throughout the whole joint. The joint having a single Cu 3 Sn phase had the highest shear strength. Specimens were aged up to 2000 h at 150°C and 180°C. During aging, the microstructures of all joints were transformed in a single Cu 3 Sn phase. The shear strength of the joints was very sensitive to the formation of Cu 3 Sn and microvoids. Microvoids formed in the solder joints with a Cu 6 Sn 5 phase with and without a Sn-rich phase during aging and decreased the shear strength of the joints. Conversely, aging did not induce the formation of microvoids in the joints which originally had only a Cu 3 Sn phase and the shear strength was not decreased.

The welding of thick high strength aluminum alloy plate was exceedingly difficult. Traditional arc welding was prone to softening the welded joints and involves multilayer; meanwhile, multi-pass welding may cause great residual welding stress, and deformation resulted in dampening the wide expansion of the welding structure of thick high strength aluminum alloy plates. Therefore, it was urgent to develop advanced materials and welding technologies to enhance the comprehensive mechanical properties of welded joints. Fiber laser boasted the advantages such as perfect monochromaticity and high quality light beam. In order to decrease the thermal loss of the welding heat source on the matrix, small power fiber laser and super narrow gap groove were applied for the effective welding of the 20-mm thick 7A52 aluminum alloy. The welding adopted multilayer and single pass welding with the groove width no wider than 4 mm. The weld was composed of four layers and the size was no wider than 4.5 mm, which was basically consistent with the widths of the whole. The parent metal was welded with 5183 alloy and 5E06 alloy. Fiber optical microscope, scanning electron microscope (SEM), transmission electron microscope (TEM), and tensile testing machine were employed to investigate the influence of Er-Zr microalloying aluminum alloy welding wires upon the microstructure and mechanical properties of the welded joints.

The shear strength behavior and microstructural effects after aging for 100 h and 1,000 h at 150°C are reported for near-eutectic Sn-Ag-Cu (SAC) solder joints (joining to Cu) made from Sn-3.5Ag (wt.%) and a set of SAC alloys (including Co- and Fe-modined SAC alloys). All joints in the as-soldered and 100-h aged condition experienced shear failure in a ductile manner by either uniform shear of the solder matrix (in the strongest solders) or by a more localized shear of the solder matrix adjacent to the Cu^sub 6^Sn^sub 5^ interfacial layer, consistent with other observations. After 1,000 h of aging, a level of embrittlement of the Cu^sub 3^Sn/Cu interface can be detected in some solder joints made with all of the SAC alloys and with Sn-3.5Ag, which can lead to partial debonding during shear testing. However, only ductile failure was observed in all solder joints made from the Co- and Fe-modified SAC alloys after aging for 1,000 h. Thus, the strategy of modifying a strong (high Cu content) SAC solder alloy with a substitutional alloy addition for Cu seems to be effective for producing a solder joint that retains both strength and ductility for extended isothermal aging at high temperatures. [PUBLICATION ABSTRACT] Key words: Lead-free solder, shear strength, joint microstructure, thermal aging

This study included a comparison of the baseline Sn-3.5Ag eutectic to one neareutectic ternary alloy, Sn-3.6Ag-1.0Cu and two quaternary alloys, Sn-3.6Ag-1.0Cu-0.15Co and Sn-3.6Ag-1.0Cu-0.45Co, to increase understanding of the beneficial effects of Co on Sn-Ag-Cu solder joints cooled at 1-3 degree C/sec, typical of reflow practice. The results indicated that joint microstructure refinement is due to Co-enhanced nucleation of the Cu sub(6)Sn sub(5) phase in the solder matrix, as suggested by Auger elemental mapping and calorimetric measurements. The Co also reduced intermetallic interface faceting and improved the ability of the solder joint samples to maintain their shear strength after aging for 72 hr at 150 degree C. The baseline Sn-3.5Ag joints exhibited significantly reduced strength and coarser microstructures.

Microstructural aspects and bonding characteristics of vacuum brazed Ti/Ti and Ti/steel were investigated. A thin-copper film, with different thicknesses, was deposited on the brazed metals by physical vapor deposition technique to serve as a brazing filler metal. Test joints were processed at a temperature of 910 °C and 15 min holding time. The resultant joints were characterized to determine the brittle intermetallic compound in the interfacial layer and the shear strength of the joints were tested. Our preliminary experimental results showed that sound joints with a good wetting quality, lack of pores and cracks can be achieved. Intermetallic phases such as Ti 2 Cu, TiCu, FeTi, and Fe 2 Ti were predicted from the chemical analyses. The Ti/Ti joints achieved a higher shear strength than the Ti/steel joints and there is a tendency for the tension shear strength to increase when a thick Cu-deposited layer is used.