Alumina–mild steel friction welded at lower rotational speed

The joining of ceramic–metal can be done using different techniques such as brazing, diffusion bonding, and friction welding. However, the mechanism of ceramic–metal joining has still not been fully understood. In this study, an alumina rod was bonded to a mild steel rod via the friction welding technique by using an Al 1100 sheet as an interlayer. The diameters of the rods were both 10 mm, respectively. A friction pressure of 20 MPa and a forging pressure of 40 MPa were used. Rotational speed was maintained at 900 rpm and friction times from 2 to 20 s were applied. The joining strength was determined through a four point bending test. The maximum bending strength, 240 MPa was obtained when the friction time of 20 s was used. Under optical microscope and scanning electron microscope observation, the bonding aluminum interface was clearly obtained. Mechanical interlocking and close contact between the alumina–aluminum and aluminum–mild steel were observed at magnifications of 3000×. The strength of alumina–steel bonding is much dependent on the wettability of the alumina surface by the partially molten aluminum interlayer and the existence of mechanical interlocking between the interlayer and mild steel.