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 recrystalization. During formation of the alloys, homogenization, solution heat treating and artificial aging processes are preferably employed.

1 . An aluminum alloy product having high strength with good toughness, containing 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.  
     
     
         2 . The alloy product of  claim 1 , wherein said alloy contains about 0.05-0.2% Zr.  
     
     
         3 . The alloy product of  claim 1 , wherein said alloy includes 0.05-0.30% Sc.  
     
     
         4 . The alloy product of  claim 3 , wherein said alloy includes 0.05-0.20% Zr.  
     
     
         5 . The alloy product of  claim 1 , wherein said alloy includes about 0.03-0.10% Si and 0.03-0.12% Fe.  
     
     
         6 . The alloy product of  claim 1 , wherein the combined weight percentages of Mg and Cu range from 4.1 to 4.5%.  
     
     
         7 . The alloy product of  claim 6 , wherein the combined weight percentages of Zn, Mg and Cu range from 13.0 to 14.5%.  
     
     
         8 . The aluminum alloy product of  claim 1 , wherein said product is selected from the group including sporting goods such as baseball and soft ball bats, golf shafts, lacrosse sticks, tennis rackets, and arrows; aerospace components such as wing plates, bulkheads, fuselage stringers, and structural extrusions and forgings; and ordnance parts such as sabots and missile launchers.  
     
     
         9 . 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.    
     
     
         10 . The process of  claim 9 , wherein said first temperature is about 30° F. below said melting temperature.  
     
     
         11 . The process of  claim 9 , 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.  
     
     
         12 . The process of  claim 9  where the alloy ingot is held at said first temperature for at least 8 hours.  
     
     
         13 . The process of  claim 9 , wherein said alloy contains 0.05-0.30 % Sc.  
     
     
         14 . 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 degrees F. and then artificially aged in a first aging step by being heated at 175-310 degrees F. for 3 to 30 hours.  
     
     
         15 . The process of  claim 14 , wherein said product is exposed to a second aging step by being heated at 310 to 360 degrees F. for 2 to 24 hours.  
     
     
         16 . The process of  claim 15 , wherein said alloy product is exposed to a third aging step by being heated at 175 to 300 degrees F. for 1 to 30 hours.  
     
     
         17 . The process of  claim 9 , 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 degrees F. for 2 to 24 hours.  
     
     
         18 . The process of  claim 17 , wherein said alloy product is exposed to a second aging step by being heated at 175 to 300 degrees F. for 1 to 30 hours.