Search

Laser–MIG hybrid welding–brazing was used to weld 304 stainless steel and 6061-T6 aluminum alloy with a thickness of 2 mm. The microstructure, morphology, chemical composition and corrosion behavior of the samples after high-temperature oxidation were investigated. The results reveal that the 304/6061 dissimilar joint had a thicker intermetallic compound layer (7–8 μm) during high-temperature oxidation (HTO) treatment than the sample without HTO treatment (2–3 μm). The oxide film thickness of the 6061 side of the weld joint treated by HTO (2401 nm) increased compared to the samples (181.1 nm) without HTO treatment. Unlike other metals treated by high-temperature oxidation, the high-temperature treatment process in this paper can reduce the corrosion resistance of the base metal and dissimilar joints, and the sequence of the corrosion current density was weld (HTO) >weld>6061 (HTO) >6061>304 (HTO) >304. [ABSTRACT FROM AUTHOR]

• IMCs-free joint of Mg/Al alloys was obtained by plating of Ni on AZ31Mg alloy. • Nano-sized Mg 2 Sn IMC was found in the Mg (Ni)/SAC/Al joint at 280 °C by TEM. • Ni coating could not stop the diffusion of Mg into solder as temperature above 280 °C. • The strength of joint with Ni coating enhanced 80.7% than that of without Ni coating. • The relationship between dissolution of Ni and diffusion of Mg was investigated. Magnesium and aluminum alloys are widely used in various industries because of their excellent properties, and their reliable connection may increase application of materials. Intermetallic compounds (IMCs) affect the joint performance of Mg/Al. In this study, AZ31 Mg alloy with/without a nickel (Ni) coating layer and 6061 Al alloy were joined by ultrasonic-assisted soldering with Sn-3.0Ag-0.5Cu (SAC) filler. The effects of the Ni coating layer on the microstructure and mechanical properties of Mg/Al joints were systematically investigated. The Ni coating layer had a significant effect on formation of the Mg 2 Sn IMC and the mechanical properties of Mg/Al joints. The blocky Mg 2 Sn IMC formed in the Mg/SAC/Al joints without a Ni coating layer. The content of the Mg 2 Sn IMC increased with increasing soldering temperature, but the joint strength decreased. The joint without a Ni coating layer fractured at the blocky Mg 2 Sn IMC in the solder, and the maximum shear strength was 32.2 MPa. By pre-plating Ni on the Mg substrate, formation of the blocky Mg 2 Sn IMC was inhibited in the soldering temperature range 240–280 °C and the joint strength increased. However, when the soldering temperature increased to 310 °C, the blocky Mg 2 Sn IMC precipitated again in the solder. Transmission electron microscopy showed that some nano-sized Mg 2 Sn IMC and the (Cu, Ni) 6 Sn 5 phase formed in the Mg(Ni)/SAC/Al joint soldered at 280 °C, indicating that the Ni coating layer could no longer prevent diffusion of Mg into the solder when the soldering temperature was higher than 280 °C. The maximum shear strength of the Mg(Ni)/SAC/Al joint was 58.2 MPa for a soldering temperature of 280 °C, which was 80.7% higher than that of the Mg/SAC/Al joint, and the joint was broken at the Mg(Ni)/SAC interface. Pre-plating Ni is a feasible way to inhibit formation of IMCs when joining dissimilar metals. [ABSTRACT FROM AUTHOR]

Zircaloy-4, which is used as a structural material for nuclear cladding, requires precise bonding at low temperature in nuclear power applications. We achieved this using diffusion bonding with Ni plating on the surface of Zircaloy-4. We evaluated the performance of joints at temperatures between 650 and 780 °C. At 650 °C, the joint was successfully bonded. The joint exhibited a maximum shear strength of 207 MPa at 780 °C, which was twice as high as that produced by direct diffusion bonding at 700 °C under the same parameters. The interface was analyzed by using a combination of SEM and TEM to identify the presence of multilayered intermetallic compound layers in the joints. We investigated the mechanism of interface generation and determined the sequence of phase formation by Gibbs free energy calculations to be NiZr, Ni 10 Zr 7 , NiZr 2 , Ni 7 Zr 2 , and Ni 3 Zr. Through X-ray diffraction and cross-section elemental analysis of the fractures, we observed that, at lower temperatures, the joint fracture tended to occur in the Ni layer, whereas at higher temperatures, it occurred between Ni 7 Zr 2 and Ni 3 Zr. The utilization of diffusion welding with Ni plating applied to the surface of Zircaloy-4 reduces the joining temperature and enhances the properties of the joint. • Achieving Zr-4/Ni/Zr-4 joint through Ni plating on the surface. • The temperature of vacuum diffusion bonding decreases after Ni plating. • Using Gibbs free energy to determine the generation order of the phases. [ABSTRACT FROM AUTHOR]

The widespread utilization of lightweight Mg and Al alloys underscores the importance of establishing reliable connections between them. However, joining dissimilar Mg/Al alloys presents challenges, primarily due to uncontrolled formation of intermetallic compounds during the process, leading to weakened joint performance. To inhibit its formation, a Ni or Ni–Al 2 O 3 nanocomposite coating served as a barrier layer during ultrasonic-assisted soldering AZ31 Mg/6061 Al using Sn–3.0Ag–0.5Cu solder. By investigating the impacts of Ni/Ni–Al 2 O 3 composite coating on microstructure, intermetallic compounds formation, and joint performance, we found that the Ni coating partially inhibited Mg diffusion into the solder at 260 °C for 20 min, thus limiting excessive Mg 2 Sn compound formation and increasing shear strength by approximately 110% compared to uncoated joints. However, with an extension of the holding time to 30 min, block-shaped Mg 2 Sn compound reemerged as the primary cause of joint failure. Using Ni–Al 2 O 3 composite coating further broadened the process window of Mg/Al soldering, eliminating block-shaped Mg 2 Sn compound in the joint at 260 °C for 40 min. The incorporation of Al 2 O 3 further enhanced joint properties, with the maximum shear strength of the Mg(Ni–Al 2 O 3)/SAC/Al joint reaching approximately 66.6 MPa, an improvement of 18.3% compared to the joint with Ni coating. This enhancement shifted the fracture position from the Ni/SAC interface to the SAC solder. Additionally, due to grain refinement in the Ni matrix, the microhardness of the Ni–Al 2 O 3 composite coating surpassed that of the Ni coating. A model of Ni/Ni–Al 2 O 3 composite coating preventing intermetallic compounds formation of was proposed. This nanocomposite coating-ultrasonic assisted soldering method effectively avoids the issue of excessive intermetallic compounds formation when joining dissimilar metals. [Display omitted] • An Al 2 O 3 nano-sol composite coating hindered Mg 2 Sn compound formation. • Proposed mechanism for Ni-based coating inhibiting Mg 2 Sn compound formation. • Ni–Al 2 O 3 composite coating further broadens the process window of Mg/Al soldering. • The strength of joint with coating was 148.5% higher than that of uncoated joint. [ABSTRACT FROM AUTHOR]

• Al/steel laser-MIG welding-brazing joints exhibit sensitivity to strain rates. • The weld reinforcement plays an important role in dynamic tensile properties and failure behavior. • DIC technology is used to observe the dynamic tensile fracture process. • Dislocation aggregation and crack deflection are the main reasons of the performance enhancement. Studies on dynamic tensile characteristics for Al/steel dissimilar materials are crucial to ensure the integrity and dependability of light-weight structures. In this study, the tensile characteristics and failure behaviors of Al/steel laser-MIG welded-brazed joints were studied. The dynamic fracture mechanisms of the joints are discussed. With the increase in strain rate, the fracture mode and tensile properties of Al/steel joints with reinforcement changed. The joints exhibited two failure modes of heat-affected zone failure at lower strain rates and interface failure at higher strain rates. When the strain rate was 1000 s−1, the increase in dislocation density in the weld reinforcement and diversion of cracks in the intermetallic compound layer significantly enhanced the joint's properties. The tensile and yield strengths reached 222.6 and 166.6 MPa, 6.5 % and 17.9 % higher than those at a stain rate of 1 s−1, respectively. For Al/steel joints without reinforcement, as the strain rate increased, the crack gradually grew to the Al 8 Fe 2 Si phase, leading to a notable enhancement in the joint's performance. At a strain rate of 500 s−1, the maximum strength of the joint reached 238.3 MPa, representing an increase of 58.9 % in comparison to the strain rate of 1 s−1. [ABSTRACT FROM AUTHOR]

• Fatigue crack propagation (FCP) in different micro-zones of aluminum/steel joints was investigated. • Single-edge notched tensile (SENT)-interface showed the highest FCP rate and crack threshold. • The FCP path of SENT-weld was deflected toward the heat-affected zone. • SENT-weld deflection is due to the effects of microstructure and micro-performance. Research on fatigue damage of aluminum/steel dissimilar joints is critical to ensure the reliability of multi-material lightweight structures. In this study, the fatigue crack propagation (FCP) characteristics of the interface, weld, and heat-affected zone (HAZ) of aluminum/steel laser-metal inert gas (MIG) fusion-brazed joints were investigated. Additionally, the influencing role of the microstructure of different micro-zones on the FCP behaviors was discussed. Single-edge notched tensile (SENT) specimens of the interface region exhibited a higher crack growth rate and crack threshold than SENT-weld and SENT- HAZ specimens due to the highly hard and brittle nature of the intermetallic compounds (IMC) at the aluminum/steel interface. Moreover, the fatigue fracture surface of SENT-interface specimens showed a brittle fracture pattern without fatigue striation characteristics, which was different from aluminum/steel solid-state and traditional aluminum alloy welded joints. Electron backscatter diffraction (EBSD) analysis results revealed that the synergistic effects of grain size, sub-grain boundaries, and micro-performance all contributed to the crack deflection of SENT-weld at a large angle to the HAZ, thereby resulting in more optimized crack resistance in the weld zone. [ABSTRACT FROM AUTHOR]

Laser-metal inert gas (MIG) hybrid welding-brazing was adopted to achieve a dissimilar metal butt joint of 6061-T6 aluminum alloy and 304 stainless steel. The effect that laser power and welding speed had upon the wettability, intermetallic compound (IMC) layer microstructure and tensile strength of the joint with and without reinforcement was investigated. The results show that the spreading width of the molten metals on both sides of the steel increased with welding heat input, where the maximum spreading width on both sides of the steel was 5.7 and 4.8 mm respectively for a welding speed of 5 mm/s and a laser power of 1000 W. The total thickness of the IMC layer increased and its morphology varied with increasing heat input. The maximum tensile strength of the joint without reinforcement was improved to 180 MPa with a welding speed of 5 mm/s and a laser power of 1000 W, which was attributed to the fact that the transformation of Fe 4 Al 13 morphology reduced the stress concentration in this layer. The tensile strength of the joint with reinforcement was up to 200 MPa (70% of the 6061-T6 tensile strength). The fracture occurred at the heat-affected zone of the 6061-T6 aluminum alloy. [ABSTRACT FROM AUTHOR]

Butt joining of AA6061 aluminum (Al) alloy and 304 stainless steel of 2-mm thickness was conducted using laser-MIG hybrid welding-brazing method with ER4043 filler metal. To promote the mechanical properties of the welding-brazing joints, two kinds of intermediate layers (Al-Si-Mg alloy and Ag-based alloy) are used to adjust the microstructures of the joints. The brazing interface and the tensile strength of the joints were characterized. The results showed that the brazing interface between Al alloy and stainless steel consisted of double layers of Fe2Al5 (near stainless steel) and Fe4Al intermetallic compounds (IMCs) with a total thickness of 3.7 m, when using Al-Si-Mg alloy as the intermediate layer. The brazing interface of the joints using Ag-based alloy as intermediate layer also consists of double IMC layers, but the first layer near stainless steel was FeAl2 and the total thickness of these two IMC layers decreased to 3.1 m. The tensile strength of the joints using Al-Si-Mg alloy as the intermediate layer was promoted to 149 MPa, which was 63 MPa higher than that of the joints using Al-Si-Mg alloy as the intermediate layer. The fractures occurred in the brazing interface between Al alloy and stainless steel. [ABSTRACT FROM AUTHOR]

A set of stainless steel plates were treated by hot-dipping into molten pure aluminum (Al) at 700C, 760C and 820C with different immersion time from 10s to 1800s. The growth behavior of the intermetallic compound layers between the substrate and Al coating is investigated. The intermetallic compounds showed a bi-layer structure consisting of FeAl3 close to Al coating and Fe2Al5 close to the substrate. The thickness of the intermetallic layers is closely related to the immersion time. Crack occurred with increasing immersion time and thickening Fe2Al5 layer. The thickness of the Fe2Al5 layers increases linearly with the square root of immersion time. Phase's identification of each layer was confirmed using X-ray diffraction (XRD) analysis by grinding the specimens to expose different layers. The Fe2Al5 layer exhibited a single intensive peak attributable to (002) plane. The full width half maximum () of Fe2Al5 on stainless steel substrate is 11.99 by X-ray rocking curve measurement, suggesting that the Fe2Al5 grains have a strong orientation texture but not a single crystal. For comparison, of Fe2Al5 formed on mild steel by hot-dipping is 14.12. The relationship between the of Fe2Al5 layers and the growth mechanisms of crystals is discussed for the two steel substrates. [ABSTRACT FROM AUTHOR]

Butt joining of an AA6061 aluminum alloy and a Ti-6Al-4V titanium alloy with a 3 mm thickness was carried out using laser-metal inert-gas hybrid welding-brazing without a bevel or an air gap. The uniformity of the interfacial intermetallic compound (IMC) layer was improved by changing the laser-arc offset and the laser-deviation angle. The weld appearance, IMC layer microstructure and tensile strength of the welded-brazed joints were investigated. A uniform serrated 1 μm thick TiAl 3 layer was formed along the butt plane by using a laser-deviation angle. The tensile strength of the joint was closely related to the IMC layer morphology and thickness. Joints with excellent wetting and spreading on both sides achieved a maximum tensile strength of 230 MPa when the laser-arc offset was 1.2 mm and the laser-deviation angle was 5°. Three different fracture phenomena existed during the tensile test that correspond to different fracture positions at the interface layer, weld seam and heat-affected zone of the aluminum base metal. [ABSTRACT FROM AUTHOR]

• A borate brazing flux is used to assist the brazing of Mn–44Cu–1.5Al alloy and 430SS. • The formation of intermetallic compounds at the joint interface is investigated. • Reductive elements, such as Al and Si, can reduce B 2 O 3 from the brazing flux to B. • Elemental B can react with Mn, Fe, and Cr to form intermetallic compounds. Intermetallic compounds (IMCs) distributed at the interface reduce the bonding strength of Mn–Cu–Al alloy/430 stainless steel (430SS) brazed joints. Here, we investigated the formation mechanism of IMCs to improve the reliability of brazed joints. Mn–Cu–Al high-damping alloy and 430SS were induction-brazed assisted by Cu–34Mn–6Ni–6Sn filler metal and borate brazing flux. Shapeless IMCs were observed to be distributed in chains at the joint interfaces. Moreover, shear cracks propagated along the IMC chains. The IMCs were determined to be (Fe, Cr, Mn) 2 B; elemental B could only come from the brazing flux according to the materials used for brazing. We propose that IMC formation consists of four stages: (i) substrate dissolution and filler metal diffusion, (ii) B 2 O 3 reduction, (iii) IMC nucleation, and (iv) needle growth and chain distribution of IMC. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Mg 2 Sn formation and growth was found mainly occurred during the cooling stage. • The Mg 2 Sn thickness was inhibited to less than 5 μm by using water-cooling. • The joint strength was improved greatly with water-cooling than that of air-cooling. • The fracture location changed from the IMC layer to the solder with water-cooling. Magnesium and aluminum alloys are widely used in various industries because of their light weight and other properties. However, Mg–Al intermetallic compounds (IMCs) decrease the joint properties of Mg/Al, which limits its applications. Here, the alloys AZ31 Mg and 6061 Al are soldered together with Sn and Sn–9Zn solders though different cooling rates via ultrasonic-assisted soldering to control IMC formation and growth. Results show that this prevents formation of Mg–Al IMCs such as Al 3 Mg 2 and Al 12 Mg 17 ; however, Mg 2 Sn forms in the soldered joints. The Mg 2 Sn thickness increases with soldering temperature, which reduces joint strength. The thickness is reduced using the Sn–9Zn solder, and the effect of Zn is analyzed. With the use of water-cooling, the Mg 2 Sn formation and growth are inhibited, the Mg 2 Sn thickness is kept below 5 μm, and the shear strength peaks at 53.2 MPa. A soldering model of Mg 2 Sn formation is proposed to reveal the evolution and inhibition mechanism of Mg 2 Sn. This study well controls IMC thickness and improves joint strength, thus expanding industrial application of Mg–Al dissimilar metals and providing a feasible method for controlling IMCs in dissimilar metal joining. [ABSTRACT FROM AUTHOR]

6-mm 6061-T6/SUS304 butt joints were obtained successfully with a breakthrough through a deep-penetration welding-brazing process using a laser hybrid metal inert gas (MIG). The laser powers were optimized to obtain a sound joint with good formation. The quality of joints was evaluated via tensile tests. Moreover, the morphology and thickness of the intermetallic compound (IMC) layer along Al/steel interface were also studied via Scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the spreading degree on the steel side of the molten metal was improved with increasing laser power, and a sound joint without visible defects was obtained when the laser power was 4150 W. Double IMC layers consisting of η-Fe 2 (Al, Si) 5 and θ-Fe(Al, Si) 3 were formed at the three interface regions regardless of the laser power. A larger number of cracks appeared at the interface as the laser power increased to 4200 W. TEM analysis revealed that characterization and thickness of the IMC layer at the interface on the top and bottom were quite distinct. The maximum tensile strength (140.7 MPa) with reinforcement was significantly higher than that of the 6 mm Al/steel fusion welding joints using laser or laser-arc keyhole welding technology. [Display omitted] • Deep-penetration welding-brazing is employed for the joining of 6-mm Al/steel butt plates. • Double IMC layers consist of Fe 2 (Al, Si) 5 and Fe(Al, Si) 3 are formed at the three interface regions. • The characterization of the IMC layer on the top and bottom are enormously distinct. • The maximum tensile strength is higher than that of 6 mm Al/steel fusion welding joints. [ABSTRACT FROM AUTHOR]