Narrow Results

Zr-4 alloys were vacuum brazed using Ag–Cu–Ti filler metal. The effect of brazing temperature on the microstructure evolution, shear strength and corresponding fracture behavior of the brazed joints was investigated. The typical phases at the brazing temperature of 800, 840 and 930^∘C were inferred to be three different microstructures, i.e., a mixture of (Cu, Ti) phases and Ag-rich phase, Ag-rich phase and brittle intermetallic compound (IMC) AgZr, and a uniformly mixed morphology of CuZr and AgZr. And the width of the whole brazed seam increased from 78.4$\mu$m to 118.8$\mu$m. Meanwhile, the shear strength of the brazed joints first increased and then decreased followed by a small increase. The maximum shear strength of 138MPa was obtained at the treatment of 800^∘C for 10min. The fracture morphology exhibited typical brittle fracture characteristics, and the cracks initiated from the interface of the brazed joints, and propagated into the intermediate zones.

This experiment chooses A356 aluminum matrix composites containing 55% SiC particle reinforcing phase as the parent metal and Al–Si–Cu–Zn–Ni alloy metal as the filler metal. The brazing process is carried out in vacuum brazing furnace at the temperature of 550°C and 560°C for 3 min, respectively. The interfacial microstructures and fracture surfaces are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy spectrum analysis (EDS). The result shows that adequacy of element diffusion are superior when brazing at 560°C, because of higher activity and liquidity. Dislocations and twins are observed at the interface between filler and composite due to the different expansion coefficient of the aluminum alloy matrix and SiC particles. The fracture analysis shows that the brittle fracture mainly located at interface of filler and composites.

Compared without electroless Ni–P alloy coating on the SiCp/Al composites, the paper describes the effect of Ni–P deposited layer on the microstructure evolution, shear strength, airtightness and fracture behavior of vacuum brazed joints. Void free and compact reaction layers along the 6063Al/Ni–P deposited layer/filler metal interfaces indicated that the joints exhibit high airtightness with He-leakage less than $2.0\times 10^{-8}$ $\mathrm{\text{Pa}}\cdot {\mathrm{\text{m}}}^3/\mathrm{\text{s}}$. Energy Dispersive X-ray Spectroscopy (EDS) analysis showed that the reaction layers mainly included brittle Al–Ni and Al–Cu–Ni intermetallics, where fracture occurred in priority and the shear strength was less than 90 MPa. However, without Ni–P alloy coating, sound joints with high shear strength of 100.1 MPa but low airtightness with He-leakage higher than $1.45\times 10^{-7}\mathrm{\text{Pa}}\cdot {\mathrm{\text{m}}}^3/\mathrm{\text{s}}$ were also obtained at 590${}^{\circ }$C for soaking time of 30 min. In this case, a few holes that occurred along the filler metal/SiC particle interface significantly decreased the compactness of the joints. Therefore, according to the requirements in practical applications, suitable choice was provided in this research.