•Copper/alumina dissimilar joints were continuous drive friction welded by using 2.5 mm thick AA1100 aluminum as interlayer.•Obvious mutual diffusion occurred at the interfaces enhancing wettability and proving metallurgical bonding.•Aluminum interlayer is essential to obtain copper/alumina joints by diminishing stress concentration and wetting alumina.•The friction interface transferred during the welding process.Wettability and stress concentration are the main challenges affecting the engineering application of copper/alumina dissimilar joints. In this paper, continuous drive friction welding of copper to alumina was conducted using 2.5 mm thick AA1100 aluminum as interlayer. The effects of friction pressure and friction time on the tensile strength of joints were evaluated, and the interface microstructure evolution and fracture morphologies were also analyzed. Obvious mutual diffusion occurred at the alumina/aluminum and aluminum/copper interfaces, enhancing wettability and proving metallurgical bonding. Microcracks formed in alumina base due to thermo-mechanical coupling effect in welding. As increasing friction pressure and friction time, the tensile strength increased till reaching a peak value of 35 MPa, and then decreased. The optimized parameters were determined as friction pressure of 12 MPa and friction time of 12 s. All samples failed at the aluminum/alumina interface, leaving a pit structure on alumina base. The application of pure aluminum interlayer is essential to obtain sound copper/alumina joints by diminishing stress concentration and wetting alumina, and the optimized residual aluminum layer is about 0.47 mm thick. The friction interface transferred from alumina/aluminum to inner plasticized aluminum layer, and then moved to aluminum/copper till the welding process finished.Download high-res image (190KB)Download full-size image

An erosion often occurs, when brazing cemented carbide with Cu–Mn based filler alloy, therefore, the binder phase erosion and interface evolution are systematically investigated. When heating, the binder phase Co dissolves into the molten filler and the erosion product acquires liquid state. Heavy WC particles successively submerge into the molten filler, while the erosion layer becomes incompact. With increasing brazing temperature, the tensile strength increases to the maximum 589MPa at 970 °C with holding for 300 sec, and then decreases to 431 MPa at 1010 °C. The microscopic fracture morphology analysis reveals that the erosion product possesses poor wettability against WC particles. When long-time heat preservation at 970 °C, a structure gradient layer is locally formed, because the de-bonded WC particles submerge into the liquid filler metal successively, which promotes the thermal stress release and obtaining high-strength joint.

In this paper, the joints between Al and Cu bars were fabricated by continuous drive friction welding. The microstructures and the compositions of the composites were analyzed by SEM, EDS and XRD. The surface temperature was observed using an infrared thermographic camera. The interface temperatures were suggested in the range of 648~723 K at different welding parameters. The interdiffusion between Al and Cu atoms is extraordinarily rapid, as the interdiffusion coefficients could reach 7.8 × 10−12 m2/s. Intermetallic phases Al2Cu and Al4Cu9 were identified in all samples in view of the XRD and EDS analyses. The effective Gibbs free energy change of formation model was proposed to predict the Al–Cu compound formation at solid-state interface, and the calculation combined with kinetic factors showed that Al2Cu (Al side) and Al4Cu9 (Cu side) appeared first.

•Germanium powders were used as interlayer to diffusion braze monocrystal silicon for their fine metallurgical compatibility.•Maximum tensile strength over 15.8 MPa had been obtained for the joint processed at 1000 °C for 3 h.•The thickness of diffusion layer was proved to be the controlling factor for the tensile strength.In this research, diffusion brazing of monocrystal silicon was performed using germanium powders as interlayer. The effects of brazing temperature (950–1050 °C) and time (1–3 h) were studied on the joint microstructure and its mechanical properties. The results indicated that, with the rise in brazing time and temperature, the morphology near the sample edge turned from sintered structures to bridge connections. While those in the center evolved from straight Ge layers to symmetric layer structures with the sequence of “Si base/Isothermal solidification zone/Athermal solidification zone/Ge layer”. Withal, the crushing and interlocking morphologies appeared. Bond strength was evaluated and maximum tensile strength over 15.8 MPa was obtained for the joint processed at 1000 °C for 3 h. Results showed that, thickness of diffusion layer (i.e., the isothermal solidification zone and athermal solidification zone) was proved to be the controlling factor for the tensile strength of diffusion brazed monocrystal silicon.

•The effect of friction time on the microstructure and joint strength was studied.•The fit of burn-off lengths at different times yields a simple equation.•The longer friction time leads to oversized flash in Ti6Al4V side and overgrown IMCs.•An IMZ with width less than 3 μm is beneficial to make a strong metallurgical bond.•The average strength of 560 MPa is obtained and higher than ever reported results.Dissimilar joint of Ti6Al4V titanium alloy and SUS321 stainless steel was fabricated by continuous drive friction welding. The effect of friction time on the mechanical properties was evaluated by hardness measurement and tensile test, while the interfacial microstructure and fracture morphologies were analyzed by scanning electron microscope, energy dispersive spectroscope and X-ray Diffraction. The results show that the tensile strength increases with friction time under the experimental conditions. And the maximum average strength 560 MPa, which is 90.3% of the SUS321 base metal, is achieved at a friction time of 4 s. For all samples, studied fracture occurred along the joint interface, where intermetallic compounds like FeTi, Fe2Ti, Ni3(Al, Ti) and Fe3Ti3O and many other phases were formed among elements from the two base metals. The width of intermetallic compounds zone increases with friction time up to 3 μm, below which it is beneficial to make a strong metallurgical bond. However, the longer friction time leads to oversized flash on the Ti6Al4V side and overgrown intermetallic compounds. Finally the optimized friction time was discussed to be in the range of 2–4 s, under which the sound joint with good reproducibility can be expected.

By using Nb/Cu/Ni structure as multi-interlayer, diffusion bonding titanium to austenitic stainless steel has been conducted. The effects of bonding temperature and bonding time on the interfacial microstructure were analyzed by scanning electron microscope equipped with energy dispersive spectroscope, and the joint strength was evaluated by tensile test. The results showed that Ni atoms aggregated at the Cu–Nb interface, which promoted Cu solution in Nb. This phenomenon forms a Cu–Nb solution strengthening effect. However, such effect would decay by using long bonding time that dilutes Ni atom aggregation, or be suppressed by using high bonding temperature that embrittles the Cu–Nb interface due to the formation of large grown intermetallic compounds. The sound joint was obtained by promoted parameters as 850 °C for 30–45 min, under which a bonding strength around 300 MPa could be obtained.Highlights► Titanium was diffusion bonded to stainless steel using Nb/Cu/Ni multi-interlayer. ► The effects of bonding parameters on microstructure and joint strength were studied. ► Nickel aggregation promotes Cu solution in Nb which can strengthen the joint. ► The sound joint with strength of around 300 MPa was obtained by promoted parameters.

Aluminum 1060 and titanium alloy Ti–6Al–4V plates were lap joined by friction stir welding. A cutting pin of rotary burr made of tungsten carbide was employed. The microstructures of the joining interface were observed by scanning electron microscopy. Joint strength was evaluated by a tensile shear test. During the welding process, the surface layer of the titanium plate was cut off by the pin, and intensively mixed with aluminum situated on the titanium plate. The microstructures analysis showed that a visible swirl-like mixed region existed at the interface. In this region, the Al metal, Ti metal and the mixed layer of them were all presented. The ultimate tensile shear strength of joint reached 100% of 1060Al that underwent thermal cycle provided by the shoulder.Highlights► FSW with cutting pin was successfully employed to form Al/Ti lap joint. ► Swirl-like structures formed due to mechanical mixing were found at the interface. ► High-strength joints fractured at Al suffered thermal cycle were produced.