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Mechanical properties of aged AI-5.8% Mg alloy at 423 and 473 K, over the ageing time range 1-35 h, have been investigated to assess the effect of ageing temperature on deformation in the presence of precipitation. The results indicate that the 0.2% yield strength, ultimate tensile strength, flow stress, work hardening exponent and ductility increase with ageing time reaching a maximum value, and then decrease to minimum value, followed by an increase at longer ageing times. The variation in yield, ultimate tensile strength, work hardening exponent of the flow, as well as the hardness at different degrees of deformation, were recorded as functions of experimental variables. Electron microscopic investigations revealed that the strengthening and loss in ductility of the alloy may be attributed to the precipitation of different shapes of MnAI 6, Mg2AI 3 and ~-Mg23AI3o, whose size, quantity and morphology depend on the experimental conditions. An attempt has been made to correlate strength, ductility and structural changes at different ageing times. The Brinell hardness increases and the recrystallization temperature decreases with deformation. From parabolic stress-strain relation, the ~_~1/2 curves could be divided into two linear parts.

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