High strength Al-Zn alloy and method for producing such an alloy product

Abstract

The present invention relates to a high strength Al—Zn alloy product with an improved combination of corrosion resistance and toughness, the alloy including essentially (in weight percent): Zn: 6.0-9.5, Cu: 1.3-2.4, Mg: 1.5-2.6, Mn and Zr<0.25 but preferably in a range between 0.05 and 0.15 for higher Zn contents, other elements each less than 0.05 and less than 0.25 in total, balance aluminium, wherein (in weight percent): 0.1[Cu]+1.3<[Mg]<0.2[Cu]+2.15. The invention also relates to a method to produce these alloy products, and to some preferred applications thereof such as upper wing applications in aerospace.

1 . A wrought high strength Al—Zn alloy product with an improved combination of corrosion resistance and toughness, said alloy comprising essentially of (in weight percent): 
 Zn 6.0 to 9.5    Cu 1.3 to 2.4    Mg 1.5 to 2.6    Nm<0.12    Zr<0.20    Cr<0.10    Fe<0.25    Si<0.25    Ti<0.10    Hf and/or v<0.25, and    optionally ce and/or sc<0.20,    other elements each less than 0.05 and less than 0.25 in total, balance aluminium, and wherein (in weight percent):    0.1[Cu]+1.3<[Mg]<0.2[Cu]+2.15.    
     
     
         2 . Alloy according to  claim 1 , wherein the amount (in weight %) of Mg is in a range of 0.2[Cu]+1.3<[Mg]<0.1[Cu]+2.15.  
     
     
         3 . Alloy according to  claim 1 , wherein the amount (in weight %) of Mg is in a range of 0.2[Cu]+1.4<[Mg]<0.1 [Cu]+1.9.  
     
     
         4 . Alloy according to  claim 1 , wherein the alloy product has an exfoliation corrosion resistance (“EXCO”) of EB or better.  
     
     
         5 . Alloy according to  claim 1 , wherein the alloy product has an exfoliation corrosion resistance (“EXCO”) of EA or better.  
     
     
         6 . Alloy according to  claim 1 , wherein the amount (in weight %) of Cu is in a range of 1.5 to 2.1.  
     
     
         7 . Alloy according to  claim 1 , wherein the amount (in weight %) of Cu is in a range of 1.5 to 2.0.  
     
     
         8 . Alloy according to  claim 1 , wherein the amount (in weight %) of Zr is in a range of 0.05 to 0.15.  
     
     
         9 . Alloy according to  claim 1 , wherein the amount (in weight %) of Mg and Cu is about 1.93 when the amount (in weight %) of Zn is about 8.1.  
     
     
         10 . Alloy according to  claim 1 , wherein the amount (in weight %) of Zn is in a range of 6.1 to 8.3.  
     
     
         11 . Alloy according to  claim 1 , wherein the amount (in weight %) of Zn is in a range of 6.1 to 8.3 and Mn is lower than 0.05.  
     
     
         12 . Alloy according to  claim 1 , wherein the amount (in weight %) of Mn is in a range of 0.06 to 0.12 when the amount of Zn is above 7.6.  
     
     
         13 . Alloy according to  claim 1 , wherein the amount (in weight %) of Fe is less than 0.12.  
     
     
         14 . Alloy according to  claim 1 , wherein the amount (in weight %) of Si is less than 0.12.  
     
     
         15 . Alloy according to  claim 1 , wherein the alloy has been artificially aged to a T79 or T76 temper in a two-step ageing procedure.  
     
     
         16 . Alloy according to  claim 15 , wherein the two-step ageing procedure consists of a first heat treatment at a temperature in a range of 105° C. to 135° C. for 2 to 20 hours, and a second heat treatment at a higher temperature than 135° C. but below 210C for 4 to 12 hours.  
     
     
         17 . Alloy according to  claim 1 , wherein the product is a plate product.  
     
     
         18 . Alloy according to  claim 1 , wherein the product is a plate product having a thickness is a range of 15 to 45 mm.  
     
     
         19 . Alloy according to  claim 18 , wherein the plate product is a thin aircraft member.  
     
     
         20 . Alloy according to  claim 18 , wherein the plate product is an elongate structural shape member of an aircraft.  
     
     
         21 . Alloy according to  claim 18 , wherein the plate product is an upper-wing member of an aircraft.  
     
     
         22 . Alloy according to  claim 18 , wherein the plate product is a thin skin member of an upper-wing of an aircraft.  
     
     
         23 . Alloy according to  claim 18 , wherein the plate product is stringer of an aircraft.  
     
     
         24 . Alloy according to  claim 18 , wherein the plate product is stringer of an upper-wing of an aircraft.  
     
     
         25 . Method for producing a wrought high-strength Al—Zn alloy product according to  claim 1  with an improved combination of corrosion resistance and toughness, comprising the steps of: 
 a) casting an ingot with the following composition (in weight percent): 
 Zn 6.0 to 9.5  
 Cu 1.3 to 2.4  
 Mg 1.5 to 2.6  
 Mn<0.12  
 Zr<0.20  
 Cr<0.10  
 Fe<0.25  
 Si<0.25  
 Ti<0.10  
 Hf and/or V<0.25, optionally Ce and/or Sc<0.20,  
   other elements each less than 0.05 and less than 0.50 in total, balance aluminium, wherein (in weight percent): 
 0.1[Cu]+1.3<[Mg]<0.2[Cu]+2.15,  
   b) homogenising and/or pre-heating the ingot after casting,    c) hot working the ingot and optionally cold working into a worked product,    d) solution heat treating and    e) quenching the solution heat treated product.    
     
     
         25 . Method according to  claim 24 , wherein the worked and solution heat-treated product is artificially aged, and wherein the ageing step comprises a first heat treatment at a temperature in a range of 105° C. to 135° C. for 2 to 20 hours, and a second heat treatment at a higher temperature than 135° C. but below 210° C. for 4 to 12 hours.  
     
     
         26 . Method according to in  claim 25 , wherein the worked and solution heat-treated product is artificially aged, and wherein the ageing step comprises a third heat treatment at a temperature in a range of 105° C. to 135° C. for more than 20 hours and less than 30 hours.  
     
     
         27 . Method according to  claim 25 , wherein the worked and solution heat-treated product is artificially aged, and wherein the ageing step consists of a first heat treatment at a temperature in a range of 105° C. to 135° C. for 2 to 20 hours, and a second heat treatment at a higher temperature than 135° C. but below 210C for 4 to 12 hours.  
     
     
         28 . Method according to  claim 24 , characterized by artificially ageing the worked and solution heat-treated product with a two-step ageing procedure to a T79 or T76 temper.  
     
     
         29 . Method according to  claim 24 , wherein after homogenising and/or pre-heating the ingot after casting, hot working the ingot and optionally cold working into a worked product having a thickness in the range of 15 mm to 45 mm.  
     
     
         30 . Method according to  claim 29 , wherein the plate product is a thin aircraft member.  
     
     
         31 . Method according to  claim 29 , wherein the plate product is an elongate structural shape member of an aircraft.  
     
     
         32 . Method according to  claim 29 , wherein the plate product is an upper-wing member of an aircraft.  
     
     
         33 . Method according to  claim 29 , wherein the plate product is a thin skin member of an upper-wing of an aircraft.  
     
     
         34 . Method according to  claim 29 , wherein the plate product is stringer of an aircraft.  
     
     
         35 . Method according to  claim 29 , wherein the plate product is stringer of an upper-wing of an aircraft.  
     
     
         36 . Alloy according to  claim 1 , wherein the amount (in weight %) of Zn is in a range of 6.1 to 8.3 and Mn is lower than 0.02.  
     
     
         37 . Alloy according to  claim 1 , wherein the amount (in weight %) of Zn is in a range of 6.1 to 7.0 and Mn is lower than 0.05.  
     
     
         38 . Alloy according to  claim 1 , wherein the amount (in weight %) of Zn is in a range of 6.1 to 7.0 and Mn is lower than 0.02.