Interfacial microstructure evolution and brazing properties of the vacuum-brazed QAl9-4/1Cr17Ni2 joints with a novel Cu-Mn-Ag-Ni-Zn filler metal

Aiming at the difficulty of existing filler metal to meet the increasingly demanding brazing properties requirements of heterogeneous joints of aluminum bronze and martensitic stainless steel in the aerospace field, a novel filler metal Cu-24Mn-14Ag-13.5Ni-4Zn-0.4Si-0.3B-0.3P for vacuum brazing of QAl9-4 aluminum bronze and 1Cr17Ni2 martensitic stainless steel was prepared. The microstructure of the new filler metal was studied, and the effects of brazing temperature and brazing time on the interface microstructure evolution and brazing properties of the brazed joint were observed. The optimal brazing process parameters were explored. In addition, the relationship between microstructure and brazing properties of brazed joints was discussed, and the key interface bonding mechanism and joint fracture mechanism were studied. The results show that the typical interface microstructure of the brazed joint can be divided into five regions, including QAl9-4 substrate/Cu(s.s) + NiAl thin strip reaction layer/Cu(s.s) + Ag(s.s) + MnFeP + NiAl block solder area/Cu(s.s) + NiAl strips + NiAl strip reaction layer/1Cr17Ni2 substrate. The existence form of NiAl and Ag(s.s) directly determines the brazing properties of the brazed joint, the NiAl layer near the 1Cr17Ni2 interface mainly plays the role of interfacial strengthening, and the blocky NiAl in the brazing zone plays the role of dispersed strengthening, and the interfacial strengthening and dispersed strengthening significantly enhance the brazing properties of the joints. The fracture cracks tend to sprout at the interface of Ag(s.s)/NiAl or Fe-Mn-P compounds where the deformation difference is large, which reducing the joints' brazing properties. Under the optimal brazing process parameters of 945 degrees C/12 min, the brazed joint corresponds to a room temperature shear strength of 356 MPa and a 500 degrees C high-temperature shear strength of 169 MPa, which is better than the data reported in the literature. The amount of silver, a precious metal, included in the new brazing material used in this study has also been reduced by 7 wt % compared to the minimum silver content of 21 wt% reported in the literature.