Constitutive constants for hot working of Al-4.5 Mg-0.35 Mn (AA5182)

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.