Surface quality study of AZ31B Mg alloy in electric pules-ultrasonic assisted incremental sheet forming

Poor surface quality is one of the main problems for the forming and application of magnesium alloys. In this study, electric pulse and ultrasonic vibration were simultaneously applied to the incremental sheet forming (ISF) process of magnesium alloys, and the effect of electric pulse–ultrasonic composite energy field on the surface quality was investigated. Compared with electric pulse–assisted forming, a composite energy field could reduce the forming force under any condition and improve the surface quality at the condition of higher current frequency (≥ 350 HZ), lower step depth (0.1 mm), and keep the effective current density less than 30 A/mm2. The maximum percentage decrease in forming force and surface roughness is about 20 and 50%, respectively. Moreover, although the surface quality can be improved by ultrasonic energy in both directions, the effect is more significantly in direction perpendicular to the feed direction than that in the direction parallel to the feed direction. The repeated rolling caused by ultrasonic vibration is benefit to the rearrangement of the surface gully and makes the surface profile height distribution relatively uniform. The surface quality also would be aggravated due to the dynamic impact of the ultrasonic vibration and serious surface oxidative, which caused by excessive temperature increasing at the condition of high current density.