A model for predicting the effect of deformation after solution treatment on the subsequent artificial aging behavior of AA7030 and AA7108 alloys

Abstract

The effect of deformation after solution treatment on the two-step artificial aging response has been examined for AA7030 and AA7108 alloys. Aging experiments were conducted where the prestrain level was varied between 0 and 1.2. It was observed that the kinetics of aging were accelerated and the magnitude of the peak strength decreased in the presence of prestrain. This was attributed to the increased growth/coarsening rate of precipitates on dislocations and the widening of the precipitatesize distribution, respectively. A model was developed based on the internal state variable approach to predict yield stress as a function of the heat treatment and the level of prestrain. The increase in the kinetics of aging was accounted for in an average sense by the use of an effective diffusion coefficient that combines bulk and short-circuit diffusion. The precipitation model was based on two variables; the average spacing between precipitates and the average strength of precipitates. The variation of the average strength of precipitates with precipitate radius was varied to account for the change in the width of the precipitate-size distribution. Static recovery of the deformed structure during artificial aging was also accounted for in a first-order approximation. Good agreement was found between the model predictions and experimental results. Additional experimental data were obtained after the model was developed, and it was observed that the model made excellent predictions.

The influence of precipitation on the work-hardening behavior of the aluminum alloys AA6111 and AA7030

“…In this case, it appears that the shearable/nonshearable transition occurs very near to the peak strength. This would be consistent with recent precipitation-hardening models by both Deschamps and Brechet [31] and Poole et al, [32] which have du>ds (a) (b) k 2 dislocation storage rate term due to dynamic recovery k D dislocation storage rate term due to geometrically necessary dislocations f, f s , f ns constants representing the modification of the dynamic recovery due to precipitate effects; subscripts s and ns refer to shearable and nonshearable precipitates F strength of nonshearable precipitates G shear modulus L spacing of precipitates on the glide plane M Taylor factor n exponent used in flow stress addition law total strain P plastic strain dislocation density overall total flow stress of the alloy ss solid solution contribution to flow stress ppt precipitation-hardening contribution to flow stress Y yield stress dislocation hardening contribution to flow stress s saturation stress for dislocation hardening contribution T line tension of the dislocation ϭ Gb 2 /2 work-hardening rate for dislocation hardening o initial work-hardening rate for dislocation contribution to flow stress overall work-hardening rate of alloy max overall initial work-hardening rate of alloy as defined in Fig. 3 d/d as defined in Fig.…”

Studies on the Work-Hardening Behavior of AA2219 under Different Aging Treatments

“…A change in the trend of H max and dH/dr can be attributed to a transition in deformation from shearable to nonshearable precipitates as the aging proceeds. This observation is in line with the precipitation-hardening models [14][15][16] in which the transition was at the peak strength for 7000-series alloys.…”

Effect of Creep Aging Process on Microstructures and Properties of the Retrogressed Al-Zn-Mg-Cu Alloy

“…At the end of creep aging tests, the RCA-270 MPa sample has the largest average MPt size and space between MPts, and the values are approximately 21.5% and 13.1% higher than those of the creep-aged sample with RCA-90 MPa temper. The main reason is that the greater applied stress can generate more dislocations in the aluminum matrix, and these dislocations increase the kinetics of the aging process [29]. Compared with the RRA process, the RCA process can increase the MPt size and the distance between MPts.…”