Fretting wear performance and mechanism of micro-arc oxidation coatings on AZ31B magnesium alloy pretreated by ultrasonic surface rolling

Magnesium alloys are emerging as a new-generation material for implantable bone applications. To enhance their fretting wear resistance, this study employed ultrasonic surface rolling (USR) as a pretreatment on AZ31B magnesium alloy, followed by micro-arc oxidation (MAO) coating deposition. Fretting wear tests were subsequently conducted in simulated body fluid under varying displacement amplitudes. Experimental results show that USR pretreatment effectively refined the grain structure and increased surface hardness. With rising static force, the MAO coating exhibited reduced porosity, increased thickness, and improved interfacial bonding strength. Fretting wear testing further revealed that at a displacement amplitude of 10 μm, oxidation wear prevailed as the primary mechanism; at 60 μm, the wear regime was characterized by a combination of mild fatigue wear, abrasive wear, and oxidation wear. The wear rate of the USR-pretreated MAO-coated sample at 600 N static force reached 0.41×10 -5 mm 3 /J, which was 71.33% lower than that of the untreated sample.