Patent ID: 8323425

Claim:
A method for non-isothermally aging an aluminum alloy comprising: heating an aluminum alloy at a first ramp-up rate to a maximum temperature below a precipitate solvus; when the aluminum alloy reaches the maximum temperature, cooling the alloy at a first cooling rate sufficient to produce a maximum number of primary precipitates wherein the first cooling rate is obtained by optimizing a precipitation growth rate ⅆ r eq ⅆ t and a nucleation rate ⅆ N ⅆ t using the following two equations: ⅆ N ⅆ t ⁢ ❘ nucleation = N 0 ⁢ Z ⁢ ⁢ β * ⁢ exp ⁡ ( - 4 ⁢ π ⁢ ⁢ r 0 2 ⁢ γ 3 ⁢ RT ⁢ ⁢ ln 2 ⁡ ( C / C eq ) ) ⁢ exp ⁡ ( - 1 2 ⁢ β * ⁢ Zt ) ⁢ and ⅆ r eq ⅆ t = D r eq ⁢ C - C eq ⁢ exp ⁡ ( r 0 / r eq ) 1 - C eq ⁢ exp ⁡ ( r 0 / r eq ) + 1 N ⁢ ⅆ N ⅆ t ⁢ ( α ⁢ r 0 ln ⁡ ( C / C eq ) - r eq ) , where N is the precipitate density number (number of precipitates per unit volume), N 0 is the number of atoms per unit volume (=1/V atom ), Z is Zeldovich's factor, ⅆ r eq ⅆ t is the precipitation growth rate, D is the diffusion constant, r eq is the precipitate radius (also called precipitate size), r 0 is the value of 2 ⁢ γ ⁢ ⁢ V atom R ⁢ ⁢ T , C 0 is the mean solute concentration by atom percentage in the alloy matrix, C eq is the mean solute concentration by atom percentage in equilibrium precipitate-matrix interface, and α is the aspect ratio of precipitates, wherein the optimization is characterized by the maximization of ⅆ N ⅆ t and the minimization of ⅆ r eq ⅆ t ; after cooling the alloy at the first cooling rate, cooling the alloy at a second cooling rate until a minimum temperature is reached wherein the growth rate of primary precipitates is equal to or substantially zero, the second cooling rate being higher than the first cooling rate; and when the minimum temperature is reached, heating the alloy at a second ramp-up rate to a temperature sufficient to produce a maximum number of secondary precipitates; the first ramp-up rate, the first cooling rate, the second cooling rate, and the second ramp-up rate causing non-isothermal aging in which an aging temperature varies continuously with time.