Strain and Strain-Rate Hardening Effects on Forming Limit Diagrams of 5083 Aluminum Alloy Sheet under Warm Stretching

摘要

Forming limit diagrams (FLDs) of an aluminum alloy (5083-O) sheet wee obtained by performing punch stretch-forming tests at various forming speeds (0.2 to 200 mm centre dot min~(-1)) at several temperature between 293 and 573 K. The forming limit strain drastically increased with decreasing speed for any strain path at high temperatures ranging from 423 to 573 K, while at room temperature the FLDs were les sensitive to speed. In order to clarify the effects of strain and strain-rate hardening, namely, the influences of the n-value and m-value in the Backofen-type constitutive equation (sigma=C epsilon~n epsilon~m), on the FLD, the Marciniak-Kuczynski analysis was conducted. By comparing the expiring the experimentally obtained FLDs with the numerical predictions, it is concluded that the improvement in formability at high temperatures and low forming speeds is due specifically to the high strain-rate hardening characteristic (high m-value) of the material. Even at high temperatures, the formability is comparatively low at high forming speeds because of the low n-value at high strain rates.