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The weather‐resistant steel S355J2W shows potential for use in the bogies of high‐speed trains operating in extremely cold regions. In this study, the mechanical properties and fracture behavior of S355J2W steel and its MAG welding joints were investigated using low‐temperature uniaxial tensile tests, Charpy impact tests, and three‐point bending tests (TPB), which play an important role in the safety and reliability of train operation. The ductility and toughness indices decreased as the temperature decreased from room temperature to −114°C, and the weld is more dangerous and prone to fracture than the base material area. The бs/бb values of WM and HAZ samples slightly increased by 3.7% and 3.8% from 20 to −114°C, respectively. And the ductile–brittle transition temperature (DBTT) of BM, WM, and HAZ were −75.6, −46.1, and −56.6°C, respectively. The fracture micro‐mechanisms were evaluated by analyzing the grain misorientation along the residual cracks using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The high‐angle grain boundaries (GBs) in the base metal were observed to greatly contribute to stopping or deflecting the crack propagation, thereby improving the low‐temperature toughness. In contrast, the cracks easily penetrate the low‐angle GBs of the weld (which made up 38% of the grain boundaries of the welds), thereby decreasing the lower temperature fracture toughness of the weld. The dislocations of S355J2W steel and the weld metal were investigated by TEM analysis. Highlights: бb, бs values of S355J2W steel, weld, and HAZ were investigated from −114 to 20°C.The DBTT of S355J2W, WZ, and HAZ were −75.6, −46.1, and −56.6°C, respectively.δm of the weld was the lowest, which means that the fracture toughness deteriorated in the weld.High‐angle grain boundaries contributed to improving the low‐temperature toughness. [ABSTRACT FROM AUTHOR]

Aluminum alloy 5083 was joined with Sn-Zn (, 5, 9, 30 and 60 wt.%) filler metal by ultrasonic soldering at 400C. The joint microstructure consisted of -Sn and -Al solid-solution phases when using pure Sn solder. Zn-rich phases were observed in the joints with Sn-Zn filler metal. The Zn-rich phases grew thicker and larger with the increase in Zn content in the filler metal. The joints soldered with Sn-30Zn filler metal reached a maximum shear strength of 70 MPa. Joint cracking occurred at the interface of pure Sn and Sn-9Zn solders as indicated by SEM observation of the fracture surfaces. The locations of the fracture surface moved from the interface to the seam when using the Sn-30Zn or Sn-60Zn filler metal. The coarse Zn-rich phases were also observed on the fracture surface using Sn-60Sn solder, which results in a shear strength reduction of the joints. [ABSTRACT FROM AUTHOR]

During the hybrid ultrasonic frequency induction brazing of tungsten carbide-cobalt/35CrMo (WC-Co/35CrMo) steel, a Ag-Cu-Zn-Mn-Ni metal was utilized as a filler metal, the vibration frequency was 21 kHz, and the brazing temperature was varied from 710 °C to 820 °C. WC particles dispersed in the bond with the ultrasonic vibration, which phenomenon did not occur during traditional brazing processes. Based on the evolution of the microstructure of the WC particles in bonds formed at different ultrasonic times, the dissolution behavior of cobalt (Co) in Ag-based filler metal was investigated. A migration model of WC particles into the bonds was proposed that enables the control of the extent of reinforcing WC particles. Compared with conventional frequency induction brazing, WC particles in the bond via this ultrasonic-assisted brazing technique strengthened the joints significantly, resulting in a shear strength increase of 17% (approximately 408 MPa). [ABSTRACT FROM AUTHOR]