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 (sigma = C epsilon (n)(epsilon) over dot (m)). The numerical results of the FLDs were in qualitative agreement with the experimental observations. (C) 2001 Elsevier Science B.V. All rights reserved.