High strength Al-Zn-Mg alloy for making shaped castings including vehicle wheels and structural components

Abstract

There is claimed an alloy composition for castings, especially vehicle wheels. This cast composition is chromium-free, zirconium-free and consists essentially of: about 4-7 wt. % zinc, more preferably, about 4-5 wt. % zinc; about 1.2-1.8 wt. % magnesium; at least one of about 0.3-0.6 wt. % manganese and 0.1-0.25 wt. % copper; up to about 0.25 wt. % iron; and up to about 0.25 wt. % silicon, the balance aluminum and incidental impurities. Products made from this alloy exhibit fatigue properties equal to or greater than those for a 6061-T6 forging, typically about 850,000 cycles at about 12.5 ksi; and about 330,000 cycles at about 20 ksi. They also exhibit a typical T6 tensile yield strength of about 50 ksi or higher.

What is claimed is:  
     
         1 . A shaped casting made from a chromium-free, zirconium-free, aluminum alloy exhibiting improved fatigue performance and a typical T6 yield strength of about 50 ksi or higher, said casting consisting essentially of: about 4-7 wt. % zinc, about 1.2-1.8 wt. % magnesium, at least one of about 0.3-0.6 wt. % manganese and 0.1-0.25 wt. % copper, up to about 0.25 wt. % iron, and up to about 0.25 wt. % silicon, the balance aluminum and incidental impurities.  
     
     
         2 . The shaped casting of    claim 1    wherein said alloy contains about  4-5  wt. % zinc.  
     
     
         3 . The shaped casting of    claim 1    wherein said alloy contains less than about 0.15 wt. % silicon and less than about 0.15 wt. % iron.  
     
     
         4 . The shaped casting of    claim 1    wherein said alloy has fatigue properties equivalent to or greater than: about 850,000 cycles at about 12.5 ksi; and about 330,000 cycles at about 20 ksi.  
     
     
         5 . A shaped casting aluminum alloy which has fatigue properties equivalent to or greater than about 850,000 cycles at about 12.5 ksi; and about 330,000 cycles at about 20 ksi and a typical T6 yield strength of about 50 ksi or higher, said casting being chromium-free, zirconium-free and consisting essentially of: about  4-7  wt. % zinc, about 1.2-1.8 wt. % magnesium, at least one of about 0.3-0.6 wt. % manganese and 0.1-0.25 wt. % copper, up to about 0.25 wt. % iron, and up to about 0.25 wt. % silicon, the balance aluminum and incidental impurities.  
     
     
         6 . The alloy of    claim 5    which contains about 4-5 wt. % zinc.  
     
     
         7 . The alloy of    claim 5    which contains less than about 0.15 wt. % silicon and less than about 0.15 wt. % iron.  
     
     
         8 . A vehicle wheel cast from a chromium-free, zirconium-free aluminum alloy consisting essentially of: about 4-7 wt. % zinc, about 1.2-1.8 wt. % magnesium, at least one of about 0.3-0.6 wt. % manganese and 0.1-0.25 wt. % copper, up to about 0.25 wt. % iron, and up to about 0.25 wt. % silicon, the balance aluminum and incidental impurities, said cast wheel having a typical T6 yield strength of about 50 ksi or higher.  
     
     
         9 . The vehicle wheel of    claim 8    which contains about 4-5 wt. % zinc.  
     
     
         10 . The vehicle wheel of    claim 8    which contains less than about 0.15 wt. % silicon and less than about 0.15 wt. % iron.  
     
     
         11 . The vehicle wheel of    claim 8    wherein said vehicle is a mid-size truck.  
     
     
         12 . A vehicular structural component cast from a chromium-free, zirconium-free aluminum alloy consisting essentially of: about 4-7 wt. % zinc, about 1.2-1.8 wt. % magnesium, at least one of about 0.3-0.6 wt. % manganese and 0.1-0.25 wt. % copper, up to about 0.25 wt. % iron, and up to about 0.25 wt. % silicon, the balance aluminum and incidental impurities, said cast structural component having a T6 tensile yield strength of about 50 ksi or higher.  
     
     
         13 . The vehicular structural component of    claim 12    which contains about 4-5 wt. % zinc.  
     
     
         14 . The vehicular structural component of    claim 12    which contains less than about 0.15 wt. % silicon and less than about 0.15 wt. % iron.  
     
     
         15 . The vehicular structural component of    claim 12    which is a control arm.  
     
     
         16 . The vehicular structural component of    claim 12    which is a steering knuckle.  
     
     
         17 . The vehicular structural component of    claim 12    which is a differential carrier.