EFFECTS AND MECHANISMS OF EXTRINSIC STRENGTHENING DURING AGING FOR AL ALLOY 2090+Ce
(Northwestern Polyteehnical University, Xi’an, Shanxi 710072, China)
Abstract: The influence of aging temperature and time on fracture feature of monotonic tensile samples of aluminum-lithium alloy 2090+Ce was investigated. The effects and mechanisms of extrinsic strengthening during aging for this alloy with a flat unrecrystallized structure were discussed. The mechanisms were analysed from four aspects. The theory of extrinsic strengthening from the delamination strengthening was presented. The resuits in this research show that the strength and ductility of aluminum-lithium alloy with a flat unrecrystallized structure are superior to those with recrystallized structure. Several reasons have been advanced for the ductility improvement effect of flat uncrystallized structure, including wedging action between flat grain, aclion of short-transverse delamination on impeding the growth of main crack, action on the reduction in the detrimental influence of weak grain boundaries and action on impeding the intergranular fracture on main fracture surface. The strengthening effect of flat uncrystallized structure is attributed to the extrinsic strengthening derived from delamination strengthening. From underage to peakage, the fracture mode of this alloy is transgranular fracture plus short-transverse delamination. The tendency of short-transverse delamination increases with aging, thereby enhancing the delamination strengthening effect. Under overaging condition, the fracture mode is predominately intersubgranular> which results in the loss of delamination strengthening.
Key words: Aluminum-lithium Alloy Aging Extrinsic Strengthening Delamination Strengthening Grain Structure