Precipitate behavior and mechanical properties of enhanced solution treated Al-Zn-Mg-Cu alloy during non-isothermal ageing

An approach combined the enhanced solution treatment (EST) and the non-isothermal ageing (NIA) treatment was employed on the as-rolled Al-Zn-Mg-Cu alloy. The hardening response is greatly affected by the precipitates size distribution and their volume fraction. The supersaturation of the EST alloy is improved since the residual constituent particles are dissolved into the matrix. During heating (100-200 degrees C), the driving force for precipitation is enhanced and the average precipitate radius is rapidly increased with elevated temperature. Higher volume fraction of precipitates are obtained at the EST-HX conditions (aged at heated X degrees C), and thus the strength values are superior to those of the traditional HX conditions. Although the coarsening takes place, the average radius of the EST-H210 condition remains smaller than that of the H210 case. And the yield strength of 515 MPa for the EST-H210 condition is still higher compared to that of 474 MPa for the H210 condition. With decreasing temperature (200-140 degrees C), the secondary precipitation in the EST-CX condition (aged at cooled X degrees C) is more easily driven by the continuous reduction of solubility. Then the average radii of the EST-CX conditions are lower than those of the CX conditions, while the corresponding volume fractions are higher. Therefore the strength values of the EST-CX conditions increase resume and retain higher. Besides, the peak strength is reached at the EST-C140 condition ahead of time, at which point the tensile strength and yield strength are 589 MPa and 558 MPa, respectively. (C) 2017 Elsevier B.V. All rights reserved.