Artificial aging control of aluminum alloys

Abstract

The present invention provides a mathematical approach to constructing a model of artificially aging to accurately calculate the value of a property in an aluminum alloy product achieved by aging the alloy. The method includes developing a formula having two independent time and temperature evolving expressions, aging the product to achieve the property by heating the product over an aging period determined by the formula and terminating the heating when the property is achieved according to a mathematical formula. The property is calculated as a function of time and product temperature measured over the aging period. Calculation of the property includes integration of the thermal effects on the product over the entire aging period.

1 . A method of artificially aging an aluminum alloy product to achieve a property value in the product wherein said property value varies in response to aging, the method comprising: (i) providing a mathematical formula expressing the property as a sum of two independently time and temperature evolving expressions, wherein a first expression dominates the behavior of the property with aging in the regime before the peak aging value of the property and a second expression dominates the behavior of the property with aging in the regime following the peak aging value of the property; (ii) heating an aluminum alloy over an aging period and terminating the aging period when the property value is achieved in accordance with evaluating over time the mathematical formula provided in step “i” for each temperature regime experienced by said product.  
   
   
       2 . The method of  claim 1  wherein the product is optionally age formed during the artificial aging process.  
   
   
       3 . The method of  claim 1  wherein the aging period optionally contains a portion during which the temperature of the article is varied and optionally contains a portion during which the temperature of the article is substantially fixed.  
   
   
       4 . The method of  claim 1  wherein the aluminum alloy product is solution heat treated prior to aging.  
   
   
       5 . The method of  claim 1  wherein the aging period contains periods during which the temperature is varied.  
   
   
       6 . The method of  claim 1  wherein the aging period is carried out at a substantially fixed temperature.  
   
   
       7 . The method of  claim 1  wherein the alloy article to be aged begins the aging period in an underaged state and the mathematical model accurately predicts the property in an aging period prior to peak aged state, proximal to a peak aged state or following the peak aged state.  
   
   
       8 . The method of  claim 1  wherein the property is selected from the group consisting of strength (e.g. tensile yield strength), fracture toughness, corrosion resistance, hardness and electrical conductivity.  
   
   
       9 . The method of  claim 1  wherein said time and temperature-domain evolving variables are X s  and X b  and wherein said time- and temperature-dependent expression of the property comprises 
         X ( t,T )= X   s   −βX   b   
     wherein X s  relates the value of the property to a dislocation shear mechanism in the alloy and X b  relates the value of the property to a dislocation bypass mechanism in the alloy, and β is a constant for the alloy.  
   
   
       10 . The method of  claim 9  wherein the aging step is terminated when the desired value for X is attained and the value of dX/dt is selected to be about zero or negative.  
   
   
       11 . The method of  claim 1  wherein the alloy is selected from the group consisting of a 2xxx, 6xxx, or 7xxx AA series alloy and AA7085 alloy.  
   
   
       12 . The method of  claim 1  wherein the product comprises an aluminum article selected from a rolled article, an extruded article, and a forged article.