Effect of Mn element on the wettability of CuZnNi brazing filler metal and the microstructure and properties of brazed joints

Element Mn with different contents were added into CuZnNi brazing filler metals, and the melting point, wetting and spreading properties and microstructure composition of CuZnNiMnx brazing filler metals were studied. Subsequently, the CuZnNiMnx brazing filler metal was used to induction braze YG8 hard alloy and Q235 steel and the effect of different Mn contents on the microstructure composition and tensile strength of the brazed joint were discussed. The results showed that when the Mn content increased from 0 to 6 wt.%, the solid-liquid phase lines of CuZnNiMnx brazing filler metal decreased from 1014.45℃ to 915.88℃, so that the wetting and spreading properties of the brazing filler metal improved. The wetting and spreading area of CuZnNiMnx brazing filler metal on the steel surface increased from 210mm² to 310mm². The microstructure of CuZnNiMnx brazing filler metal was mainly composed of α-Cu solid solution and β(β ')Cu-Zn solid solution. With the increase of Mn content, the proportion of α-Cu solid solution decreased and the proportion of β (β ') Cu-Zn solid solution increased. When the Mn content increased to 6wt.%, the two kinds of phase generated segregation. The induction brazed joint between YG8 hard alloy and Q235 steel was mainly composed of Co-Cu-Ni solid solution in the interface of brazing seam and YG8 hard alloy, also α-Cu solid solution and Cu-Zn alloy in the brazing seam center. The tensile strength of the brazed joint increased first and then decreased with the Mn content increasing. When the Mn content was 4 wt.%, the tensile strength of the brazed joint reached the maximum value of 325 MPa.