Method for tempering an aluminum alloy

Abstract

A process for tempering large aluminum lithium alloy component parts to achieve high strength capability and resistance to stress corrosion cracking without the need for the prior art step of cold working the alloy components parts. The process achieves the desired material properties by the use of two novel soaking time periods and the use of novel controlled temperature selection at the two respective soaking times as well as carefully controlling the temperature decrease from one soaking time period to the other.

1 . A process for tempering an aluminum alloy blank to achieve high strength capability and resistance to stress corrosion cracking, said process comprising the steps of:
 annealing said alloy blank in accordance with Aerospace Material Specification AMS 2770 for 2XXX aluminum alloy;   hot spinning the annealed alloy blank into a desired shape at a first controlled temperature;   solution heat treating said desired shape in accordance with SAE Aerospace Material Specification AMS 2770 using a set temperature of 950° F.±10° F. for a time in accordance with AMS 2770 Table 3;   rapidly quenching said desired shape in a liquid;   a first aging said desired shape to a second controlled temperature;   a first soaking of said desired shape at a first predetermined length of time;   lowering the second controlled temperature of said desired shape at a predetermined rate of decrease to a third controlled temperature;   a second soaking of said desired shape at a second predetermined length of time; and   air cooling said desired shape until said desired shape reaches room temperature.   
     
     
         2 . The process of  claim 1  comprising the additional step after said quenching step of:
 straightening said desired shape to remove minor distortions that may be introduced by said quenching step. 
 
     
     
         3 . The process of  claim 1  comprising the additional step of:
 testing said desired shape to determine the properties of said desired shape. 
 
     
     
         4 . The process of  claim 3  wherein said testing step has a least one test selected from the group of tests consisting of hardness, electrical conductivity, mechanical ASTM test, and a SCC test. 
     
     
         5 . The process of  claim 1  wherein said quenching liquid is water. 
     
     
         6 . The process of  claim 1  wherein said quenching liquid is a glycol water solution. 
     
     
         7 . The process of  claim 1  wherein said first controlled temperature is in the range of 725 degrees F. 
     
     
         8 . The process of  claim 1  wherein said second controlled temperature is in the range of 340 degrees F. 
     
     
         9 . The process of  claim 1  wherein said third controlled temperature is in the range of 250 degrees F. 
     
     
         10 . The process of  claim 1  wherein said temperature rate of decrease is in the range of 45 degrees F. per hour. 
     
     
         11 . The process of  claim 1  wherein said first soaking time is in the range of 32 hours. 
     
     
         12 . The process of  claim 1  wherein said soaking time is in the range of 72 hours. 
     
     
         13 . The process of  claim 1  wherein said aluminum alloy blank is made from 2195 aluminum lithium alloy. 
     
     
         14 . The process of  claim 1  wherein said desired shape is a domed top of a rocket. 
     
     
         15 . The process of  claim 1  wherein said desired shape is a thrust cone of a rocket.