Interfacial structure and fracture behavior of 6061 Al and MAO-6061 Al direct active soldered with Sn–Ag–Ti active solder

• MAO–Al2O3 layer was synthesized on 6061 alloy using the micro-arc oxidation method.
• Direct active soldering of Al/MAO–Al2O3 was performed using Sn–Ag–Ti filler in air.
• The Ti reacts with the MAO–Al layer to form both Ti-oxidized or rich-Ti (Al, Sn)3.

Micro-arc oxidation (MAO), a novel coating method capable of depositing compact, ultra-hard ceramic composite coatings on Al and its alloys, is applied to heat sink surfaces. A micro-porous Al2O3 layer was synthesized on 6061 Al-Alloy (MAO–Al) using the MAO technique. The microstructure, shear strength and fracture of Al/Al, MAO–Al/MAO–Al, and Al/MAO–Al joints were determined after direct active soldering in air with the Sn3.5Ag4Ti(Ce) active solder at 250 °C for 30 s. During active soldering, Al dissolves into SAT solder to form a coarse Al–Ag–Sn solid solution around the solder. Also, the active element Ti concentrates to and reacts with the MAO–Al layer to form both Ti-oxidized (e.g., TiO and TiO2) or rich-Ti(Al,Sn)3, and subsequently Ag3Sn nanoparticles are adsorbed at the solder/MAO–Al interfaces. The shear-tested bonding strengths were 15.3 ± 1.38 MPa for Al/Al, 10.45 ± 1.53 MPa for MAO–Al/Al, and 8.25 ± 1.53 MPa for MAO–Al/MAO–Al joints. In the Al/Al specimen, the fracture occurred in Al–Ag–Sn compounds of the active matrix after shear testing. In the MAO–Al/MAO–Al and MAO–Al/Al specimens, the fracture occurred in the MAO–Al/active solder interface.