The influences of duty cycle on the bonding strength of AZ31B magnesium alloy by microarc oxidation treatment

The process of microarc oxidation was studied as a pre-treatment for adhesive bonding of magnesium alloys. Porous microarc oxidation films on AZ31B magnesium alloy were prepared in a sodium silicate electrolyte by a high-frequency bipolar pulsing mode. The influences of duty cycle on film porosity and lap-shear strength of the bonding joints were studied. The higher duty cycle increased the film porosity and slightly decreased the thickness of the oxide film. The microarc oxidation film consisted mainly of MgO and MgSiO3. The increase of duty cycle resulted in the increase of MgO in the oxide film. As the duty cycle increased, the lap-shear strength increased. The highest lap-shear strength 24.5 MPa was obtained under the duty cycle of 40%. The reason was attributed to the larger porosity and enhanced mechanical interlocking effect.