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 to provide increased tensile strength without sacrificing toughness. In addition, small amounts of scandium are also preferably employed to prevent recrystalization. Preferred ranges of the elements include by weight, 8.5-11.0% Zn, 1.8-2.4% Mg, 1.8-2.6% Cu, 0.05-0.30% Sc and at least one element from the group Zr, V, or Hf not exceeding about 0.5%, the balance substantially aluminum and incidental impurities. During formation of the alloys, a homogenization process is preferably employed after alloy ingot casting in which a slow rate of temperature increase is employed as the alloy is heated as near as possible to its melting temperature. For the last 20-30 F below the melting temperature, the rate of increase is limited to 20 F/hr. or less to minimize the amount of low melting point eutectic phases and thereby further enhance fracture toughness of the alloy.

1 . An aluminum alloy product having high strength with good toughness, containing by weight, 8.5-11.0% Zn, 1.8-2.4% Mg, 1.8-2.6% Cu, 0.05-0.30% Sc 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 0.03-0.25% Zr.  
     
     
         3 . The alloy product of  claim 1 , wherein said alloy includes 8.8-10.2% Zn, 1.8-2.2% Mg and 2.0-2.4% Cu.  
     
     
         4 . The alloy product of  claim 3 , wherein said alloy includes 0.05-0.10% Sc.  
     
     
         5 . The alloy product of  claim 4 , wherein said alloy includes 0.06% Sc.  
     
     
         6 . The alloy product of  claim 1 , wherein said alloy includes 9.0-10.0% Zn, 1.8-2.2% Mg, 2.0-2.4% Cu and 0.05-0.10% Sc.  
     
     
         7 . The alloy product of  claim 1 , wherein said alloy includes 0.06% Sc.  
     
     
         8 . The alloy product of  claim 1 , wherein said alloy includes about 0.03-0.10% Si and 0.03-0.12% Fe.  
     
     
         9 . 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.  
     
     
         10 . A process for making an aluminum alloy product containing at least Al, Zn, Mg and Cu, 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.    
     
     
         11 . The process of  claim 10 , wherein said first temperature is about 30° F. below said melting temperature.  
     
     
         12 . The process of  claim 10 , 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.  
     
     
         11 . The process of  claim 10  where the alloy ingot is held at said first temperature for at least 8 hours.  
     
     
         12 . The process of  claim 10 , further comprising the step of solution heat treating the alloy ingot at said second temperature.  
     
     
         13 . The process of  claim 10 , wherein said alloy ingot contains 8.5-11.0% Zn, 1.8-2.4% Mg, 1.8-2.5% 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.  
     
     
         14 . The process of  claim 13 , wherein said alloy contains 0.05-0.30% Sc.  
     
     
         15 . The process of  claim 13 , wherein said alloy contains about 0.03-0.25% Zr.  
     
     
         16 . The process of  claim 15 , wherein said alloy contains 0.05-0.30% Sc.  
     
     
         17 . The process of  claim 13 , wherein said alloy ingot contains 8.8-10.2% Zn, 1.8 2.2% Mg and 2.0-2.4% Cu.  
     
     
         18 . The process of  claim 17 , wherein said alloy ingot contains 9.0-10.0% Zn, 1.8-2.2% Mg and 2.0-2.4% Cu.  
     
     
         19 . The process of  claim 18 , wherein said alloy includes 0.05-0.10% Sc.  
     
     
         20 . The process of  claim 19 , wherein said alloy includes 0.06% Sc.  
     
     
         21 . The process of  claim 17 , wherein said alloy includes 0.05-0.10% Sc.  
     
     
         22 . The process of  claim 21 , wherein said alloy includes 0.06% Sc.  
     
     
         23 . An aluminum alloy product having high strength with good toughness, containing by weight, 9.0-11.0% Zn, 1.8-2.4% Mg, 2.2-2.6% 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.  
     
     
         24 . The alloy product of  claim 23 , wherein said alloy contains about 0.03-0.25% Zr.  
     
     
         25 . The alloy product of  claim 23 , wherein said alloy includes 9.0-10.2% Zn, 1.8-2.2% Mg and 2.2-2.4% Cu.  
     
     
         26 . The alloy product of  claim 25 , wherein said alloy includes 0.05-0.10% Sc.  
     
     
         27 . The alloy product of  claim 26 , wherein said alloy includes 0.06% Sc.  
     
     
         28 . The alloy product of  claim 23 , wherein said alloy includes 9.0-10.0% Zn, 1.8-2.2% Mg, 2.2-2.4% Cu and 0.05-0.10% Sc.  
     
     
         29 . The alloy product of  claim 23 , wherein said alloy includes 0.06% Sc.  
     
     
         30 . The alloy product of  claim 23 , wherein said alloy includes about 0.03-0.10% Si and 0.03-0.12% Fe.  
     
     
         31 . The aluminum alloy product of  claim 23 , 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.