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Sintered NdFeB permanent magnets and steel were soldered successfully using Zn-Sn alloy. The effects of Sn content on the microstructure and mechanical properties of soldered joints were investigated. The results showed that the typical interfacial microstructure represented NdFeB/NdFe5.5Zn(B) + ξ-FeZn13/Zn + β-Sn/ξ-FeZn13 + δ-FeZn10 + Γ-Fe3Zn10/steel. With the addition of Sn, the thickness of the NdFe5.5Zn(B) phase increased, while more β-Sn was observed in the soldering seam. The maximum shear strength reached 45.3 MPa with a Sn proportion of 6 wt.%, and excessive growth of the NdFe5.5Zn(B) phase in the joints deteriorated the mechanical properties. The fracture morphology exhibited a ductile-to-brittle transition with the occurrence of interfacial fractures due to thick intermetallic compounds.

Vacuum diffusion brazing of tungsten based powder alloy and superalloy GH907 was conducted using Cu-25Ni-5V-7.5Ti (wt.%) interlayer. The typical interfacial microstructure and elements diffusion behavior were characterized. Furthermore, the effect of brazing temperature and holding time on microstructure and mechanical properties of joints were also investigated. The results showed that an undulating reaction layer and a diffusion layer with the thickness of 7.2 μm were formed adjacent to the tungsten based powder alloy, indicating good metallurgical bonding. An infiltration zone with a concentration of active elements V, Ti was formed at the superalloy GH907 side. (Cu, Ni) solid solution matrix with great plasticity was observed in the interlayer, in which some Cu4Ti3 and Ni2V phases were distributed. The joints brazed at 1100 °C for 40min exhibited the maximum shear strength of 171.6 MPa at room temperature, and the shear strength of 113.8 MPa was maintained at the test temperature of 400 °C due to the residual V, Ti particles dispersed in (Cu, Ni) solid solution matrix.

In this study, an attempt to investigate a coupling modification method for grain refinement in Zn-Sn-Cu-Bi (ZSCB) high-temperature solder has been made. During coupling modification, primary grains nucleated from CeZn5 sites and grew to form much more e-CuZn5 phases compared with the original solder. Peritectic η-Zn phases were also refined, transformed from matrix to equiaxed phases, with grain size of 1.40–2.24 µm and uniform elements distribution was achieved. By means of coupling modification, the mechanical properties of ZSCB high-temperature solder, the tensile strength and elongation, show indeed significantly improvement with an increase of 77.15% and 112.68%, respectively.

In this study, novel Zn-Sn-xBi high-temperature solders were designed to join sintered NdFeB permanent magnets and steel. The effect of Bi addition on the corrosion resistance and mechanical properties of the soldered joints was systematically investigated. The results indicated that introducing Bi with specific content obviously decreased the undercooling of the solder. Reducing the undercooling by promoting the solidification process and the formation of Bi precipitates as nucleation sites could refine the microstructure. The improvement of corrosion resistance was attributed to the finer microstructure and the Bi precipitates serving as anodic barriers. Moreover, the sound soldered joints were obtained with finer β -Sn dendrites and a more uniform distribution of Bi precipitates when appropriate Bi was added. The shear strength of the soldered joint with 5 wt% Bi addition was 36.6% higher than the shear strength of the ZS soldered joint.

In this paper, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffractometer (XRD) were used to comprehensively analyze the microstructure and brazing performance of a CuAgTi filler metal with braze tungsten heavy alloys. The association of microstructure, wettability and shear strength of brazing joints was also investigated. With the addition of Ti, the Ti3Cu4 phase appeared in the microstructure of filler metal. Ti is active element that promotes the reaction of filler with tungsten. Therefore, the Ti element is enriched around tungsten and forms a Ti2Cu layer at the interface, leaving a Cu-rich/Ti-poor area on the side. Remaining Ti and Cu elements form the acicular Ti3Cu4 structure at the center of the brazing zone. The wettability of filler metal is improved, and the spreading area is increased from 120.3 mm2 to 320.9 mm2 with the addition of 10 wt.% Ti. The shear strength of joint reaches the highest level at a Ti content of 2.5 wt.%, the highest shear strength is 245.6 MPa at room temperature and 142.2 MPa at 400 &deg, C.