Effect of injection pressures in multifunction cavitation treatment on pit formation on the surface of AZ31 magnesium alloy

This study investigated pit formation on the surface of AZ31 magnesium alloy under multifunction cavitation generated by a high-pressure water jet with ultrasonic superposition. Processing was conducted at injection pressures ( Pi ) of 20–35 MPa and stand-off distances ( Ds ) of 55–75 mm. At Ds = 65 mm, increasing Pi reduced the severity of pitting and surface roughness; however, relatively pronounced pitting was still observed. When the Ds was varied, the severity of pitting decreased in the downstream region at all Pi values due to jet attenuation and an increase in cavitation number. Evaluation of the cavitation number showed that it increased downstream, indicating that a more spatially uniform distribution of collapse impacts contributed to improved suppression of pit formation. • Pit formation on AZ31 Mg alloy was investigated under multifunction cavitation. • Injection pressure controlled the cavitation number and bubble collapse behavior. • Higher pressure reduced severity of pitting via spatial dispersion of collapse impacts. • Stand-off distance governed the cavitation-cloud development and collapse location. • Collapse localization rather than cavitation intensity dominated pit formation.