Behaviors of oxide film at the ultrasonic aided interaction interface of Zn–Al alloy and Al2O3p/6061Al composites in air

Ultrasonic aided interactions between Zn–Al alloy and Al2O3p/6061Al composites were investigated. Ultrasonic vibration imposed on the composite plate can cause high cavitation intensity in the liquid Zn–Al alloy which disrupts and flakes off surface oxides, thereby allowing the Zn–Al alloy to wet the bare composite surfaces and form a metallurgical bond. Whether the undermining phenomena occurred or not, the spreading of Zn–Al liquid over the composite did not occur until the ultrasonic vibration amplitude reached 10 μm. The Zn–Al liquid spread quickly over the composite despite that the surface oxide had not been fully disrupted when the ultrasonic vibration higher than 10 μm was applied. When undermining phenomena occurred during interaction, the oxide layer at the interaction interface was firstly lifted up by the undermining alloy, suspending in the Zn–Al liquid, and subsequently broke up by the ultrasonic excitation. Gas escaping from the base metal was observed to be helpful in decohesion of the oxide layer from the composite. When undermining phenomena did not occur during interaction, the removal of the oxide layer was based upon the melting of the nether base metal. The disruption of oxide initiated from the composite surface where the drop center located and the surface oxide layer near the drop edge was lastly removed.