A study of serrated flow, strain rate sensitivity, and formability in an aluminum-magnanese-magnesium alloy.

摘要

The present investigation was undertaken to observe the serrated flow at various temperatures and strain rates for AA 3004 aluminum alloy in regard to the related mechanical property variations. Different AA 3004 aluminum alloy conditions result in different types of serrations even at the same strain rate and test temperature. The serrated flow phenomena are associated with the dynamic interaction between diffusing solute atoms and mobile dislocations. It was found that Mg atoms are responsible for the serrated flow in the alloy, while Mn atoms in solid solution appear to retard the dynamic strain aging event.; The strain rate sensitivity of AA 3004 aluminum alloy is a strong function of the deformation temperature. From room temperature up to 125{dollar}spcirc{dollar}C, m values remain negative, however, at 150{dollar}spcirc{dollar}C the strain rate sensitivity changes in sign from negative to positive. This change of sign in the m values appears to be related to a thermally activated deformation mechanism and the dynamic precipitation of Mg{dollar}sb2{dollar}Si.; For AA 3004-H19 material, the behavior of the total elongation with respect to the deformation temperature shows a similar trend to the m values with respect to deformation temperature. The total elongation increases through an increase in strain rate sensitivities causing rapid increases in post-uniform elongation. Above 150{dollar}spcirc{dollar}C at which the positive strain rate sensitivity occurs, nearly half of the total elongation comes from beyond the maximum load. For cast material total elongation increases steadily with deformation temperature up to 150{dollar}spcirc{dollar}C, and then it decreases with an increase in temperature up to 200{dollar}spcirc{dollar}C. The post-uniform strain increases with an increase in m values. A maximum in the variation of the work hardening rate with deformation temperature represents a manifestation of the PL effects.; The temperature compensated strain rate sensitivities (m{dollar}spprime{dollar}) determined from the slopes of log {dollar}sigma{dollar} versus log {dollar}.epsilon{dollar}exp(Q/RT) turn out to be positive. It can be predicted that during the can making process the strain rate sensitivity of AA 3004-H19 materials is slightly positive.; It is found that the best uniaxial tensile parameter for predicting cup heights is total elongation. It was observed that in the cups strained to fracture, crack propagation occurred in sheet directions of minimum r value, i.e., parallel to the rolling direction. The r values linearly increase with an increase in post-uniform elongation. (Abstract shortened by UMI.)