With global environmental regulations strictly restricting Sn-Pb solders, developing high-performance lead-free solders has become a critical challenge for ensuring electronic device reliability and advancing green manufacturing. Driven by rapid technological progress in the global electronics and information industry, performance requirements have increasingly shifted toward reliability under extreme operating conditions. However, conventional lead-free solders are often plagued by excessively coarse primary crystals and overdeveloped intermetallic compound (IMC) layers. This paper reviews recent advancements in modifying traditional lead-free solders, including Sn-Cu, Sn-Zn, Sn-Bi, and Sn-Ag-Cu systems, and provides an in-depth analysis of the mechanisms underlying composite modification via trace element alloying and nanoparticle doping. Trace element alloying regulates the microstructure through solid solution strengthening and second-phase strengthening, while nanoparticle doping provides heterogeneous nucleation sites to refine grains and inhibit IMC growth. Furthermore, this study proposes the introduction of magnetic field-assisted regulation. By utilizing a uniform magnetic field to suppress particle agglomeration and guide grain orientation at the kinetic level, defects such as coarse second-phase precipitates and nanoparticle clustering are effectively mitigated. The synergistic integration of external field assistance and compositional design compensates for the inherent limitations of alloying and doping alone. This approach transcends traditional additive modification, offering new perspectives for the development of next-generation electronic packaging materials.

The high-quality welding of the Cu/Sn/Cu dissimilar metal three-layer structure was realized innovatively by electromagnetic pulse welding technology. The interfacial microstructure characterization results indicate that a transition layer composed of Cu6Sn5 and Cu3Sn forms at the Cu flyer/Sn interface. A transition layer with only Cu3Sn phase is formed at the Cu substrate/Sn interface, which is half the width of the transition layer at the Cu flyer/Sn interface. In addition, three structural models of Cu/Sn, Cu/Cu3Sn/Sn, and Cu/ Cu3Sn + Cu6Sn5/Sn were established, and the tensile failure behavior was investigated using molecular dynamics simulation. The results show that the tensile strengths of Cu/Sn and Cu/Cu3Sn/Sn structures are 6.75 GPa and 6.50 GPa, respectively. The atomic strain of these two models is primarily concentrated on the Sn side, and the failure also occurs on this side. The tensile strength of the Cu/Cu3Sn + Cu6Sn5/Sn structure is the lowest, which is 6.13 GPa. The atomic strain is mainly concentrated in the Cu3Sn + Cu6Sn5 layer, where complete fracture occurs. The tensile test results show that the fracture occurs at the interface of Cu flyer/Sn, which is consistent with the simulation results. The fracture of the Cu/Cu3Sn + Cu6Sn5/Sn structure is mainly due to the proliferation of 1/6 〈112〉 Schockley dislocation. The high dislocation density leads to local stress concentration, which easily leads to the generation and rapid propagation of cracks in the brittle phase of Cu6Sn5, ultimately causing fracture at the Cu3Sn + Cu6Sn5 layer.

This study systematically investigates the influence of discharge energy (20, 30, and 39 kJ) on the interfacial microstructure of Al/Mg heterostructures joined by electromagnetic pulse welding (EMPW). Experimental characterization confirms that high-velocity impact during welding elevates the interfacial temperature to the recrystallization thresholds of both Al and Mg, inducing dynamic recrystallization. This process results in the formation of a gradient nanocrystalline structure, characterized by a progressive transition from ultrafine nanocrystals to coarse grains. The degree of recrystallization was observed to increase with discharge energy. Molecular dynamics simulations were employed to compare the mechanical behavior of this gradient structure with that of a homogeneous nanocrystalline structure possessing an equivalent average grain size. Simulation results indicate that the gradient structure exhibits enhanced yield strength. The strengthening mechanism is ascribed to the coordinated distribution of stress and strain enabled by the structural gradient: Coarse-grained regions preferentially sustain the principal stress load, promoting dislocation multiplication and storage, thereby improving strength. In parallel, fine-grained regions facilitate plastic strain accommodation, contributing to ductility. As a result, the gradient architecture enables a synergistic improvement in both strength and plasticity.

Cu/Sn/Cu sandwich structure with asymmetric double interfaces was fabricated via electromagnetic pulse welding technology. The interface waveform formation is attributed to the coupling mechanism of fluid dynamics, material plastic instability, and energy dissipation. At the Cu flyer/Sn interface, localized melting induced by rapid local heating, followed by ultrafast cooling, facilitated efficient liquid-phase diffusion. This promoted the formation of a two-phase mixed intermetallic compound layer (Cu6Sn5 and Cu3Sn), confirming metallurgical bonding. Conversely, at the Cu substrate/Sn interface, energy dissipation constrains kinetic/thermal energy input and limits the diffusion to the solid-state regime, which is dominated by short-range diffusion at the grain boundary. Consequently, only steady-state Cu3Sn developed under high-pressure conditions.

The effectiveness of electromagnetic pulse welding is predominantly governed by the collision angle and impact velocity. This study investigates the micro-scale interfacial bonding mechanism of Copper/Copper electromagnetic-pulse welding via molecular dynamics simulations. The simulations reveal that the wavy interface formation results from plastic deformation caused by interfacial instability upon collision, accompanied by the emission of a metallic jet. Simulations with controlled collision angles show that a small angle does not generate a wavy interface. Furthermore, as the angle increases, jet atoms undergo repeated collisions between the plates, leading to the formation of a wavy interface. However, beyond a critical angle, the frequency of these reciprocal collisions decreases, consequently reducing the wavy interface frequency. Furthermore, analysis of the average interface temperature establishes the correlation between metal jets and wavy interface formation. Collision velocity simulations indicate that increased velocity promotes interfacial wave generation. Regional pressure analysis reveals that the effective interfacial length at a discharge energy of 39 kJ is less than that observed at 35 kJ.

The influence of post weld heat treatment (PWHT) temperatures on the microstructure and corrosion resistance of laser cladded Inconel 625 coatings was investigated. The elements composition test indicates that the content of Fe changes sharply in the fusion zone between the coating and substrate, as well as overlap zone of coating layers. The microstructure observation shows that as welded Inconel 625 coating is mainly composed of columnar gamma-Ni, Laves and seldom MC. The size of dendrites show an increase tendency with an increase in PWHT temperatures. There is no obvious difference in precipitates of the coating heat treated at 650 degrees C compared with the as welded. After heat treated at 750 degrees C, a small amount of needle shaped delta phase precipitates. With a further increase in PWHT temperatures, a large number and continuous of delta phase forms, while the overall amount of delta phase seems to decrease when heat treated at 950 degrees C. Electrochemical tests indicate that the (Rt), self corrosion potential (Ecorr), and pitting potential (Epit) show increase tendency, while self corrosion density (Icorr) shows opposite trend with an increase in PWHT temperatures less than 750 degrees C. When the temperatures are larger than 850 degrees C, Rt, Ecorr and Epit decrease, while Icorr increase. It is concluded that heat treated at temperatures not exceed 750 degrees C are benifit to improve resistance to initiate corrosion, uniform corrosion, and pitting.

The Al0.5CoCrFeNi high-entropy alloy (HEA) exhibits a dual-phase structure comprising body-centered cubic (BCC) and face-centered cubic (FCC) phases. Developing HEAs with superior mechanical properties through advanced additive manufacturing (AM) technologies holds significant research value. In this study, the Al0.5CoCrFeNi HEA was successfully fabricated using direct energy deposition (DED) technology, and its phase composition, microstructure evolution, and mechanical properties were systematically investigated. The results indicate that the alloy predominantly consists of the FCC phase, with a minor fraction consisting of the BCC phase. The DED sample exhibits a strong metallurgical bond with the substrate. Due to varying cooling rates, the deposited layer sequentially transitions from cellular grains at the bottom, to columnar grains in the middle, and finally to equiaxial grains at the top. The BCC phase is mainly distributed in the interdendritic (ID) regions, whereas the FCC phase dominates the dendritic (DC) regions, with the highest BCC concentration observed in the reaction layer. Within the DED sample, a gradient variation in BCC phase content was observed along the deposition direction. The DED Al0.5FeCoCrNi HEA exhibits superior strength and ductility compared to HEAs produced by conventional methods. Solid-solution and precipitation strengthening mechanisms jointly enhance the hardness at the reaction layer of the sample compared to the other regions. This study advances the fabrication of HEA systems via AM technologies and provides theoretical insights for designing HEAs with improved mechanical properties.

With the global enforcement of environmental regulations restricting the use of lead-based solders, the development of lead-free solder alloys for electronic packaging has become a central topic in ensuring both device reliability and sustainable manufacturing. This review summarizes the current research progress on lead-free solders for electronic packaging, focusing on the performance characteristics and modification strategies of major alloy systems such as Sn-Cu, Sn-Zn, Sn-Bi, Sn-Ag, and Sn-Ag-Cu. Although each system exhibits unique advantages, challenges such as high melting temperature, poor wettability, oxidation susceptibility, and high material cost remain unresolved. Performance optimization can be effectively achieved through alloying element doping and nanoparticle reinforcement. Alloying elements refine the microstructure via solid-solution strengthening, grain refinement, and secondary-phase strengthening while suppressing the coarsening of intermetallic compounds (IMCs). Meanwhile, nanoparticles enhance interfacial stability through dispersion strengthening and diffusion barrier effects, thereby improving wettability, mechanical strength, and long-term reliability. Finally, this paper proposes potential research directions for the next generation of lead-free solders and provides an outlook on their future applications in advanced electronic packaging.

The purpose is to explore the welding principle and interface bonding mechanism of electromagnetic pulse welding technology and understand the microstructure and properties of welded joints, the production and application of electromagnetic pulse welding technology in actual industry are further promoted. This paper provides a comprehensive review of this technology. The equipment and characteristics of electromagnetic pulse welding are outlined, along with its circuit device and system. The principles and parameters of electromagnetic pulse welding are discussed, including the circuit principle and combination principle. Furthermore, this study highlights the outstanding performance of the microstructure and properties of electromagnetic pulse welding, and the simulation progress of related equipment components and experimental process parameters. Finally, the future research focus and development trends are explored. It provides a reference for further promoting the wide application and rapid development of electromagnetic pulse welding technology. It provides a reference for accelerating the development of electromagnetic pulse welding technology and putting it into industrial production, extensively.

The wavy interface, a characteristic feature of electromagnetic pulse welding (EMPW), remains a subject of ongoing debate regarding its formation mechanisms. Through molecular dynamics (MD) simulations of the EMPW process, this study reveals that the periodic interfacial undulations originate from the reciprocating erosion dynamics between the metal jet expelled from the flying plate and the substrate surface, ultimately generating alternating crest-trough morphology. Systematic parametric analysis demonstrates that interfacial morphology undergoes phase transitions governed by impact velocity. furthermore, an optimal impact angle of approximately 20 degrees facilitates the formation of the wavy interface. Microstructural characterization confirms significant grain refinement at the collision interface, with the joint strength exhibiting positive correlation to discharge energy. Notably, at 35 kJ discharge energy, the joint strength reaches 35.1 MPa, approximating the base aluminum material's strength (38 MPa). This strength equivalence induces fracture location transition from the welded interface to the aluminum substrate.

Fine-grained samples of Inconel 625 (IN625) superalloy were fabricated using ultrasonic-assisted wire arc additive manufacturing (UA-WAAM). Both UA-treated and non-UA-treated samples underwent solution treatment (ST) at 1200 degrees C to achieve a homogeneous microstructure and complete recrystallization. The mechanical properties of UA-WAAM IN625 were evaluated at room temperature (RT) and 650 degrees C, and compared with WAAM IN625. The results showed that complete recrystallization eliminated the columnar grain structure and dislocations. The microstructure is composed of numerous recrystallized grains and annealed twins. Compared to the ST samples, the UA + ST samples exhibited smaller grain sizes, a higher density of recrystallized grains, and more annealing twins. All samples displayed significant ductility at RT. The tensile curves at 650 degrees C for both samples showed type C serrated behavior after surpassing the yield point, continuing until fracture. Intergranular cracks caused by grain boundary sliding and voids from stress concentration at the triple junction were the main causes of high-temperature failure. The UA-treated samples showed superior mechanical properties at both RT and 650 degrees C, due to the enhanced hindering effect of grain boundaries/twin boundaries on dislocations in fine grains. The findings of this study demonstrated the significant effects of UA and ST on the high-temperature properties of IN625 superalloy produced by WAAM.

LA103Z magnesium-lithium alloy is a new type of ultra-light metallic alloy, which is widely used in defense, military and civilian fields. In this paper, LA103Z joints with superior tensile strength and plasticity were fabricated by friction stir welding (FSW). The relationship between microstructure and tensile strength of the joints is investigated. Though the existing the phases, namely alpha-Mg, n-Li, gamma and 0 are not changed, due to recrystallization effects, the alpha-Mg phase morphology is transformed from block to spherical shape, while being also refined. Moreover, the content of nano-scale 0 phase increases, with a concomitant decrease of the gamma phase, occurs in both the stir zone (SZ) and heated affected zone (HAZ). Additionally, the n-Li phase is recrystallized and transformed into equiaxed grains from the banding grains. The microhardness is increased from 55Hv to 70Hv and 76Hv in HAZ and SZ, respectively. The ultimate tensile strength and the average elongation of the joint are 216 MPa and 63 %, which reach 124 % and 115 % of the base metals (BM), respectively, since the cooperative effect of the equiaxed n-Li phase and the nano-scale 0 phase.

In this paper, the influence of flyer strength on the deformation behavior, interface morphology, and mechanical properties of aluminum/steel EMPW joints is investigated. A comprehensive analysis is conducted to evaluate the deformation of the flyer within the effective welding area, interface characteristics, and mechanical properties of the resultant joint. The flyer deformation progressively intensifies, exhibiting a wave-like pattern that mirrors the microscopic interface deformation of the joint. At a flyer strength of 239.5 MP, the joint achieves an optimal balance of strength, hardness, and flyer deformation, demonstrating the best mechanical properties with a maximum load of 4.39 KN and an IMC layer thickness of 3.26 μm. The aluminum–steel EMPW interface evolves from flat to wavy with protrusions and eventually forms a continuous wavy transition layer as flyer strength decreases. Fe2Al5 and FeAl3 predominate in the composition of the transition layer, according to XRD and EDS studies.

Sn-9Zn eutectic alloy is a promising candidate for replacing Sn-Pb solder in electronic packaging due to its eutectic temperature (198 degrees C) close to that of Sn-Pb eutectic alloy, low toxicity, and abundant material supply. However, it exhibits disadvantages such as inferior wettability and a significant mechanical property mismatch between interfacial intermetallic compounds (IMCs) and the Cu substrate in solder joints, which adversely affects joint tensile performance. Herein, silicon carbide (SiC) nanoparticles were selected as interface-active multifunctional reinforcements. Sn-9Zn-xSiC (x = 0, 0.2, 0.4, 0.6, 0.8 wt%) composite solders and corresponding micro-solder joints (Cu/Sn-9Zn-xSiC/Cu) were fabricated by vacuum melting and reflow soldering, respectively. The influence of nano-SiC on the wettability and microstructure of Sn-9Zn eutectic alloy, as well as on the interfacial characteristics and tensile strength of the joints, was systematically investigated. Results demonstrate that nano-SiC segregation at grain boundaries reduces the interfacial tension of the molten alloy, significantly enhancing the wettability of the Sn-9Zn solder. Concurrently, nano-SiC refines the alloy's microstructure via grain boundary strengthening and dispersion strengthening, improving microhardness. The IMCs formed at the joint interface were identified as Cu5Zn8 and Cu6Sn5. Nano-SiC inhibits the excessive growth of IMCs by impeding the diffusion of Sn and Zn atoms, reduces IMC layer thickness, and increases tensile strength compared to SiC-free joints. With an optimal addition (0.4 wt%), nano-SiC simultaneously reduced the wetting angle by 34 % in the Sn-9Zn alloy, decreased the IMC layer thickness by 65.6 %, and enhanced the joint tensile strength by 27 %. Fractography revealed a ductile fracture mode with characteristic dimples. This study provides significant insights for advancing the development and practical application of high-performance, cost-effective Sn-Zn-based alloys.

The electromagnetic pulse welding (EMPW) method stands out for its rapid welding time, superior precision, and high automation, making it ideal for materials with significant melting point differences, specifically copper and tin, which often struggle to form robust joints. Utilizing molecular dynamics simulations, this study aims to investigate the interface evolution patterns under varying collision velocities and assess the welding strength of joints subjected to distinct tangential velocities. The findings reveal a profound correlation between the diffusion coefficient, system temperature, and the collision velocity during the simulated EMPW vertical collision. Specifically, at a collision velocity of Vz = 500 m/s, the interface tends to be linear, suggesting an unstable bonding state. However, when the collision velocity exceeds 700 m/s, a more intense diffusion of copper and tin atoms is observed, resulting in a wavy interface indicative of enhanced bonding capabilities. Furthermore, the study examines the shear behavior of welded joints subjected to oblique collisions with varying tangential velocities. The analysis reveals a transition in fracture locations from the joint-joint interface to the joint-base material interface and ultimately to the base material itself, as the tangential velocity increases from 50 m/s to 100 m/s and surpasses 200 m/s. This comprehensive evaluation of EMPW process variables provides a theoretical foundation for optimizing the mechanical properties of copper-tin EMPW joints.

Elevated concentrations of intermetallic compounds (IMC) in micro-solder joints adversely affect their mechanical properties. To elucidate damage evolution trends in these joints with varying IMC thicknesses under multi-field coupling, an initial IMC evolution model was formulated by employing the phase-field method. By adjusting current densities, models with diverse IMC thicknesses were generated. Experimental investigations, including IMC evolution analysis and tensile testing, determined critical damage parameters, enabling the formulation of a scalar damage model specific to micro-solder joints. Statistical analysis revealed that as IMC thickness increased, anodic damage remained confined within the IMC layer, while cathodic damage transitioned from the IMC layer to the IMC-Sn solder interface, ultimately damaging the Sn solder layer. Additionally, thicker IMC micro-solder joint models exhibited damage at lower separation displacements and encompassed larger damage areas.

The high-strength and creep-resistant Mg-Al-Ca-Mn alloys have broad application prospects. However, solidification cracking occurs in these alloys in certain conditions and the origin is still unclear. This work investigated the relationship between the solidification path, microstructure evolution and solidification cracking behavior of the Mg-xAl-2Ca-Mn alloys during tungsten inert gas (TIG) welding. Results show that when the fusion zone's Ca/Al mass ratio ranges from 0.4 to 1.64, solidification cracking occurs at a Ca/Al mass ratio of similar to 0.7. As the Ca/Al mass ratio approaches this value, the grain size increases, and the Laves phases are reduced gradually. The early formed Laves phases play an important role in promoting dendrite segmentation, refining grain size and enhancing grain boundaries. When a solidification path delays the formation of Laves phases, the Laves phases will be reduced accompanied by grain coarsening. In such a solidifying microstructure, intergranular cavitation is easy to occur, and the resistance of the semi-solid alloy to crack propagation is severely reduced.(c) 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

NiTiNb shape memory alloy (SMA) is considered to have great potential in aerospace due to its wide phase-transformation hysteresis. Here, we innovatively used electron-beam additive manufacturing (EBAM) to fabricate a NiTiNb SMA thin-walled structure. The phase-transformation temperature, microstructure evolution, and mechanical properties were investigated in detail. The as-built NiTiNb SMA comprised a NiTi matrix and different morphologies of β-Nb phase at room temperature. The microstructure homogeneity and mechanical properties of NiTiNb prepared by EBAM significantly improved compared with those of NiTiNb powder-based AM technology. Our work provided a promising method for the preparation of defect-free and microstructure homogeneous NiTiNb SMA by AM. This method further stimulated the potential of additively manufactured SMA components for industrial applications.

The rapid development of electronic packaging industry has raised stringent demands for electronic packaging interconnection materials. Currently, incorporating foreign reinforcements into solders stands as the most viable and promising approach to boosting their reliability. This study introduces a novel composite solder, Sn-3.0Ag-0.5Cu (SAC305) doped with nanonetwork-structured xCoNiO2-RGO nanosheets (x = 0, 0.01, 0.02, 0.03, 0.04, 0.06, 0.08, 0.1 wt.%), prepared via powder metallurgy. Phase and microstructure analyses were conducted using an X-ray diffractometer (XRD) and a field emission scanning electron microscope (FESEM), while mechanical properties were assessed using a Vickers hardness tester and dynamic mechanical analysis (DMA). Results indicated that nanonetwork-structured CoNiO2 was chemically anchored to both surfaces of RGO nanosheets, which were prepared via hydrothermal and solvothermal methods. The addition of CoNiO2-RGO (0~0.1 wt.%) notably refined β-Sn phases in SAC305, maintaining its melting point. The interfacial intermetallic compound (IMC) thickness initially decreased then increased, reaching its minimum at 0.02 wt.% CoNiO2-RGO nanosheets. This reduction was attributed to the interfacial adsorption effect of RGO nanosheets. While this increase was attributed to the aggregation of RGO nanosheets and the promotion of nucleation by network-structured CoNiO2 nanosheets. Correspondingly, the solder joint achieved its maximum tensile strength, peaking at 53.0 MPa at 0.02 wt.% CoNiO2-RGO nanosheets. These results suggest that traces of CoNiO2-RGO nanosheets can efficiently improve the interfacial bonding strength and solderability of the solder joint.

The thermal-mechanical-electrical-diffusion strongly coupled equations are established, and the phase field method is employed to investigate the dynamic simulation of intermetallic compound (IMC) evolution at the Cu/Sn/Cu micro-solder joint interface. By comparing with experimental results on IMC evolution in micro-solder joints, this study explores the evolution law of IMCs under the influence of current, temperature, and applied load coupling. Both simulation and experimental findings indicate that higher current density promotes IMC formation, with the largest average thickness observed at a current density of 5000 A/m2. When the analog current density is 5000 A/m2, the anode IMC has a rapid growth period at 62 h, and the corresponding cathode has a rapid consumption period; when the analog current density is 4000 A/m2, the anode has the same phenomenon in 95 h; when the analog current density is 3000 A/m2, this phenomenon is not evident. The observed phenomena are consistent with the evolutionary trend of IMC from the fourth to the fifth day of the experiment, considering it may be affected by 'electronic wind stress' which makes the cathode IMC migrate to the anode. The average thickness of IMCs with an analog ambient temperature of 323-353 K is the largest, which is most suitable for the growth of IMCs. The experimental results also indicate that IMC growth is the fastest at 353 K. The anode IMC was inhibited by tensile stress and shear stress, but the effect on cathode was not obvious.