Effect of natural aging on microstructure and properties of Al-6.5Zn-2.3Mg-2.2Cu aluminum alloy thick plate
The production processes of commercial 7 ××× series aluminum alloy products typically include a period of natural aging before artificial aging.The duration of natural aging directly affects the production process of the product.This study investigated the mi-crostructure and properties of industrially-fabricated Al-6.5Zn-2.3Mg-2.2Cu alloy thick plates after artificial aging at different stages of natural aging,focusing on the effects of short-term natural aging(0.125 to 21 days)and long-term natural aging(30 to 360 days)on the alloy in different aging states.The results indicate that during natural aging from 0.125 to 21 days,the strength of the T6-tempered alloy consistently decreases,with reductions in tensile strength and yield strength of 14 MPa and 17 MPa,respectively,while the elongation fluctu-ates within the range of 13.6％to 15.6％.The primary precipitates in the matrix are GPII zones and η'phases,and the grain boundary precipitates are discontinuously distributed.During natural aging from 3 days to 360 days,the strength,elongation,and fracture tough-ness of the T6-tempered alloy fluctuate within a certain range without a clear pattern,with the primary precipitates in the matrix being densely-distributed η'phases and the grain boundary precipitates being discontinuously distributed.During natural aging from 3 days to 105 days,the tensile properties and fracture toughness of the T76-tempered alloy also fluctu-ated within a certain range without a clear pattern,with the primary precipitates in the matrix being coarse and sparsely distributed η'and η phases,and the grain boundary precipitates being discontinuously distributed.
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