High strength aluminum alloys and process for making the same

Abstract

High strength aluminum alloys based on the Al—Zn—Mg—Cu alloy system preferably include high levels of zinc and copper, but modest levels of magnesium, to provide increased tensile strength without sacrificing toughness. Preferred ranges of the elements include by weight, 8.5-10.5% Zn, 1.4-1.85% Mg, 2.25-3.0% Cu and at least one element from the group Zr, V, or Hf not exceeding about 0.5%, the balance substantially aluminum and incidental impurities. In addition, small amounts of scandium (0.05-0.30%) are also preferably employed to prevent recrystallization. During formation of the alloys, homogenization, solution heat treating and artificial aging processes are preferably employed.

1 . A process for making an aluminum alloy product containing 8.5-10.5% Zn, 1.4-1.85% Mg, 2.25-3.0% Cu, and at least one element from the group Zr, V, or Hf not exceeding about 0.5%, the balance substantially aluminum and incidental impurities, said method including the steps of:
 casting said alloy product to form an alloy ingot; and   homogenizing said alloy ingot to minimize the amount of low melting point eutectic phases therein by heating said ingot at a heating rate of no more than 20° F./hr. from a first temperature at least about 20° F. below the melting temperature of said ingot to a second temperature of about 5° F. below said melting temperature.   
   
   
       2 . The process of  claim 1 , wherein said first temperature is about 30° F. below said melting temperature. 
   
   
       3 . The process of  claim 1 , wherein said first temperature is selected to be about 870° F. and said second temperature is selected to be in the range of 885-890° F. 
   
   
       4 . The process of  claim 1  where the alloy ingot is held at said first temperature for at least 8 hours. 
   
   
       5 . The process of  claim 1 , wherein said alloy contains 0.05-0.30% Sc. 
   
   
       6 . The process of  claim 9 , wherein said alloy ingot is formed into a shape of a finished product, solution heat treated at 870 to 900° F. and then artificially aged in a first aging step by being heated at 175-310° F. for 3 to 30 hours. 
   
   
       7 . The process of  claim 6 , wherein said product is exposed to a second aging step by being heated at 310 to 360° F. for 2 to 24 hours. 
   
   
       8 . The process of  claim 7 , wherein said alloy product is exposed to a third aging step by being heated at 175 to 300° F. for 1 to 30 hours. 
   
   
       9 . The process of  claim 1 , wherein said alloy ingot is formed into a shape of a finished product, solution heat treated and then artificially aged in a first aging step by being heated at 310 to 360° F. for 2 to 24 hours. 
   
   
       10 . The process of  claim 9 , wherein said alloy product is exposed to a second aging step by being heated at 175 to 300° F. for 1 to 30 hours.