The effects of temperature and forming speed on the forming limit diagram for type 5083 aluminum–magnesium alloy sheet

The effects of forming speed and temperature on the forming limit diagram (FLD) were investigated experimentally for a fine-grain Al–Mg alloy (5083-O) sheet by performing stretch-forming tests at various forming speeds (0.2–200 mm min−1) at several temperatures from 293 to 573 K. The forming limit strain increased drastically with decreasing speed for any strain paths at a high temperature ranging from 423 to 573 K, while at room temperature the FLD was not so sensitive to speed. The improvement in formability at 573 K at low forming speed is specifically due to the high strain-rate hardening characteristic (m-value) of the material, but below 475 K the formability is also affected strongly by strain-hardening (n-value). Furthermore, the FLDs were determined analytically based on the Marciniak–Kuczynski concept of localized necking using the Backofen-type constitutive equation (σ=Cεnε̇m). The numerical results of the FLDs were in qualitative agreement with the experimental observations.