Experimental investigation on the springback of AZ31B Mg alloys in warm incremental sheet forming assisted with oil bath heating

Magnesium (Mg) alloy sheets have attracted considerable attention as one of the most promising lightweight structural materials for weight reduction–oriented industries owing to their excellent properties compared with conventional materials. However, basal-textured Mg alloy sheets exhibit extremely inferior formability at room temperature due to their hexagonal close-packed structure and the limited number of active slip systems. Herein, an innovative warm incremental sheet forming assisted with oil bath heating approach to form difficult-to-form metal materials is proposed. To examine the forming quality of the approach, using springback as an evaluation index, a sequence of tests was conducted while forming AZ31B Mg alloy sheets according to a central composite design including response surface methodology and analysis of variance. The results indicated the approach was able to form Mg alloy sheets with great feasibility. The forming temperature (A), forming angle (B), step depth (C), and sheet thickness (D) are substantial factors that affect the springback, whereas the tool diameter (E) has a much less influential role compared with the individual effects of the other parameters, and the reasons for these results are explained. All the remaining interactive terms are substantial interactive factors except the AB, AE, BE, and CD terms, and a quadratic regression model gives the best fit with a 95% confidence level for springback. It was also indicated from the optimization results that to achieve a minimum springback value, the 166.3 °C forming temperature, 50.4° forming angle, 0.22-mm step depth, 1.18-mm sheet thickness, and 11.5-mm tool diameter should be selected.