Torsion tests on as hot rolled Al- 4.5, Mg-0.35 Mn alloy were conducted ove
r the ranges 0.1 to 10 s(-1) and 200 to 500 degreesC. As temperature increa
sed and strain rate decreased, the flow curves exhibited peaks which were l
ower and broader, followed by lower softening and closer approach to a stea
dy state regime. This occurred partly because fracture occurred at higher s
trains. In constitutive analysis, the power law was found to be inappropria
te but the exponential law was suitable. The hyperbolic sine function was f
ound to fit more closely with stress multipliers between 0.04 and 0.06 MPa-
1. The activation energy was found to be 208 kJ/mol but after correction wa
s 185 kJ/mol. These results were shown to be in reasonable agreement with p
revious studies when allowance was made for variations in composition and m
icrostructure.