Effect of Al–Si alloy coating on interfacial reactions and tensile strength in Ti/Al dissimilar brazing joints

We used ultrasonic-assisted brazing to join Al–Si-coated Ti alloys and Al alloys with a Zn–Al–Si filler metal. At the interface between the Ti alloy and Al-0.1Si alloy coating, a block TiAl₃ phase formed. In contrast, for the Al-5Si alloy coating, the interfacial reaction layer of the joint consisted of a block Ti(Al,Si)₃ phase and needle-like Ti₇Al₅Si₁₂ phase. Finally, a granular Ti₇Al₅Si₁₂ phase was formed at the joint interface for the Al-12Si alloy coating. The tensile strength of the joints formed with the Al-0.1Si and Al-12Si alloy coatings was only 160 – 185 MPa, and cracks propagated mainly through the reaction layer. The tensile strength of the joints formed with the Al-5Si alloy coating ranged from 210 to 215 MPa, and cracks appeared entirely within the coating, subsequently expanding along the coating and ultimately resulting in failure of the joint.