HIGH STRENGTH, HIGH STRESS CORROSION CRACKING RESISTANT AND CASTABLE Al-Zn-Mg-Cu-Zr ALLOY FOR SHAPE CAST PRODUCTS

Abstract

The present invention provides an Al—Zn—Mg—Cu casting alloy that provides high strength for automotive and aerospace applications and optimized stress corrosion cracking resistance in highly corrosive and tensile environments. The inventive alloy composition includes about 3.5 wt. % to about 5.5 wt. % Zn; about 1.0 wt. % to about 3.0 wt. % Mg; about 0.5 wt. % to about 1.2 wt. % Cu; less than about 1.0 wt. % Si; less than about 0.30 wt. % Mn; less than about 0.30 wt. % Fe; and a balance of Al and incidental impurities.

1 . An aluminum alloy comprising:
 about 3.5 wt. % to about 5.5 wt. % Zn;   about 1.0 wt. % to about 3.0 wt. % Mg;   about 0.5 wt. % to about 1.2 wt. % Cu;   less than about 1.0 wt. % Si;   less than about 0.30 wt. % Mn;   less than about 0.30 wt. % Fe; and   incidental impurities.   
     
     
         2 . The aluminum alloy of  claim 1  comprising a total Mg and Zn content less than or equal to 6.0 wt. %. 
     
     
         3 . The aluminum alloy of  claim 1  further comprising at least one grain refiner selected from a group consisting of boron, carbon and combinations thereof. 
     
     
         4 . The aluminum alloy of  claim 3 , wherein said at least one grain refiner includes boride in a range from about 0.0025 wt. % to about 0.05 wt. %. 
     
     
         5 . The aluminum alloy of  claim 3 , wherein said at least one grain refiner includes carbide in a range from about 0.0025 wt. % to about 0.05 wt. %. 
     
     
         6 . The aluminum alloy of  claim 1  further comprising at least one anti-grain growth agent selected from the group consisting of zirconium, scandium and combinations thereof. 
     
     
         7 . The aluminum alloy of  claim 6 , wherein said at least one anti-grain growth agent includes zirconium in a range below 0.2 wt. %. 
     
     
         8 . The aluminum alloy of  claim 6 , wherein said at least one anti-grain growth agent includes scandium in a range below 0.3 wt. %. 
     
     
         9 . The aluminum alloy of  claim 1 , wherein said zinc is at a concentration of about 4.2 wt. % to 4.8 wt. %. 
     
     
         10 . The aluminum alloy of  claim 1 , wherein said magnesium is at a concentration of about 1.2 wt. % to 1.8 wt. %. 
     
     
         11 . The aluminum alloy of  claim 1 , wherein said copper is at a concentration of about 0.6 wt. % to about 0.9 wt. %. 
     
     
         12 . The aluminum alloy of  claim 11 , wherein said copper is at a concentration of about 0.7 wt. % to 0.8 wt. %. 
     
     
         13 . The aluminum alloy of  claim 1 , wherein a concentration of iron in said alloy is less than about 0.3 wt. %. 
     
     
         14 . The aluminum alloy of  claim 1 , wherein a concentration of manganese in said alloy is less than about 0.3 wt. %. 
     
     
         15 . A method of making a shaped casting comprising:
 providing an aluminum melt comprising about 3.5 wt. % to about 5.5 wt. % Zn; about 1.0 wt. % to about 3.0 wt. % Mg; about 0.5 wt. % to about 1.2 wt. % Cu; less than about 1.0 wt. % Si; less than about 0.30 wt. % Mn; less than about 0.30 wt. % Fe; and incidental impurities;   casting at least a portion of the melt into a mold to provide a shaped casting; and   heat treating the shaped casting to an overaged condition.   
     
     
         16 . The method of  claim 15  wherein, heat treating the shaped casting to the overaged condition further comprises:
 heating the shaped casting from about room temperature to about 250° F. (actually it is a range between 200 to 300° F.) within a time period of one hour; and   aging the shaped casting at a temperature greater than about 340° F. for greater than about four hours.   
     
     
         17 . The method of  claim 16 , wherein the temperature of the aging of the shaped casting ranges from about 340° F. to about 380° F. for greater than four. 
     
     
         18 . The method of  claim 16 , wherein the aluminum melt further comprises a total Mg and Zn content of less than or equal to 6.0 wt. %.