The joint shear strengths of the AA6061/alumina joints with Al10.8 Si10 Cu, Al10 Si10 Cu4 Ti and Al10 Si10 Cu4 Ti0.1 RE filler alloys are shown in Fig. 4.2 The joint with the Al10.8 Si10 Cu fuller alloy separated at the beginning of the shear test, so the joint shear strength was not obtained. Although, the Al10.8 Si10 Cu filler alloy can be spread on the alumina under a  
Fig. 4.3 The microstructures under BSE mode of the AA6061/alumina joints with (**a**) Al10.8 Si10 Cu, (**b**) Al10 Si10 Cu4 Ti and (**c**) Al10 Si10 Cu4 Ti0.1 RE filler alloys after brazing at 530 \({}^{\circ}\)C for 10 min. small pressure during the joining process, and there is no obvious defect in the interface between Al10.8 Si10 Cu filler alloy and alumina. Since there is no metallurgical reaction, that results in almost no bonding strength between Al10.8 Si10 Cu filler alloy and alumina. The highest shear strengths of the AA6061/alumina joints with Al10 Si10 Cu4 Ti and Al10 Si10 Cu4 TiO.1 RE filler alloys were 11.7 and 19.2 MPa, respectively. The shear strength of the AA6061/alumina joint with the Al10 Si10 Cu4 TiO.1 RE filler alloy was significantly higher than that of the joint with the Al10 Si10 Cu4 Ti filler alloy. The average shear strengths of the AA6061/alumina joint with Al10 Si10 Cu4 Ti and Al10 Si10 Cu4 TiO.1 RE filler alloys were 8.0 and 14.8 MPa, respectively. The role of titanium in Al-Si-Cu filler is the same as the titanium-containing filler metals, such as tin-based [13; 14; 15], silver-based [9; 10] and indium-based [11] filler alloys, which can promote the wetting of the filler on the ceramic surface and the interfacial reaction between the filler and the ceramic. The fractography of joints brazed with Al10.8 Si10 Cu filler alloy after shear tests is shown in Fig. 4.4 All the filler alloy was on the fracture surface of the AA6061 side of the joint brazed with Al10.8 Si10 Cu filler metal after the shear test. Many particles of Al\({}_{2}\)Cu intermetallic compounds and Si-rich phase were found on the fracture surface of the AA6061 side, and no filler alloy was observed on the alumina surface side. These results indicated that the Al10.8 Si10 Cu filler alloy could not form a wetting reaction on the alumina, which led to the joint having almost no strength. Fractography of the AA6061/alumina joint with the Al10 Si10 Cu4 Ti filler alloy revealed that the brazed joint fractured along the filler metal/alumina interface, as shown in Figure 12a,b. After the shear test, most of the Al10 Si10 Cu4 Ti filler alloy was on the AA6061 surface, and very little filler metal was observed on the alumina surface. Figure 13a,b show the fractography of an AA6061/alumina joint with Al10 Si10 Cu4 TiO.1 RE filler alloy after shear test. Both of the fractured surfaces of the AA6061 and alumina were covered with Al10 Si10 Cu4 TiO.1 RE filler alloy. Since more residual attached filler alloy was observed on the alumina surface of the AA6061/alumina joint brazed with Al10 Si10 Cu4 TiO.1 RE filler alloy than on the joint brazed with Al10 Si10 Cu4 Ti alloy, high AA6061/alumina joint strength was achieved by brazing with the Al10 Si10 Cu4 TiO.1 RE filler alloy at 530 \({}^{\circ}\)C for 10 min. Fig. 4.5 The shear strengths of AA6061/alumina joints bonded with Al10.8 Si10 Cu, Al10 Si10 Cu4 Ti and Al10 Si10 Cu0.1 RE filler alloys. Fig. 4.6 Fractography of the aluminum alloy/alumina joint bonded with the Al10.8 Si10 Cu filler alloy: (**a**) AA6061 side and (**b**) alumina side. Fig. 4.7 _Cont._  
Fig. 4.8 Fractography of the aluminum alloy/alumina joint bonded with the Al10 Si10 Cu4 Ti filler alloy: (**a**) AA6061 side and (**b**) alumina side. Fig. 4.9 Fractography of the aluminum alloy/alumina joint bonded with the Al10 Si10 Cu4 Ti0.1 RE filler alloy: (**a**) AA6061 side and (**b**) alumina side.