Study on forming limit of single-point progressive forming of AZ31B magnesium alloy under isothermal local loading

In this paper, the subject of research is the AZ31B magnesium alloy. Aiming at the poor formability of magnesium alloys at room temperature, we have introduced isothermal local loading technology to improve the formability of magnesium alloys. We combined finite element simulations and experiments to study the effects of forming parameters on the forming limit angle and thinning rate of single-point incremental forming under isothermal local loading. The conclusions were further validated by changes in grain size in micrographs. The results showed that the forming limit angle of the AZ31B magnesium alloy sheet increased as the forming temperature increased. Maximum thinning first decreased and then increased, reaching the lowest point at 250 °C. At 250 °C, the grain size is large and evenly distributed, which is the best forming temperature. The radius of the tool head increases, the forming limit angle increases, the maximum thinning rate decreases, and the overall change of the average grain size is relatively small. However, the grain size is more uniform when the radius is 5 mm, and 5 mm is the best tool radius. The feed rate is inversely proportional to the forming limit angle and directly proportional to the maximum thinning rate. Different feed rates have different degrees of compression and elongation of the grains. The forming quality is better when the feed rate is 2 mm. The initial plate thickness is proportional to the limit angle, the maximum thinning rate, and grain size. And 1 mm is the best plate thickness to ensure the forming quality. This paper is important for developing the forming theory of isothermal local loading that can improve the high-performance forming of alloy parts in advanced manufacturing.