Warm Hemming of Magnesium Sheet

Magnesium sheet has received increasing interest for automotive body and closure applications. However, implementation of these applications faces many challenges involving room temperature formability. Hemming a closure panel with a magnesium outer panel will be difficult because of the sharp bend radius. Bending behavior of AZ31B-O at elevated temperatures was investigated to approximate the hemming of closure panels with acceptable surface appearance. Surface quality from small-radius bending was quantified as a function of temperature between 180 and 300 °C. Flanging with a 1.5 mm die radius yielded an acceptable surface quality at 210 °C and higher. Hemming required a minimum temperature of 270 °C for an acceptable surface condition with a 2 mm outer radius. The complex pattern of grain size and morphology of the deformed microstructure was documented with respect to the elevated temperature deformation behavior of Mg alloys. These results suggest that Mg can be hemmed at elevated temperatures with a small radius (∼1½ times the sheet thickness) and therefore could be used for vehicle closures.