HIGH STENGTH 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 . (canceled) 
   
   
       2 . The method according to  claim 25 , wherein the amount (in weight %) of Mg is in a range of 0.2[Cu]+1.3<[Mg]<0.1[Cu]+2.15. 
   
   
       3 . The method according to  claim 25 , wherein the amount (in weight %) of Mg is in a range of 0.2[Cu]+1.4<[Mg]<0.1[Cu]+1.9. 
   
   
       4 . The method according to  claim 25 , wherein the alloy product has an exfoliation corrosion resistance (“EXCO”) of EB or better. 
   
   
       5 . The method according to  claim 25 , wherein the alloy product has an exfoliation corrosion resistance (“EXCO”) of EA or better. 
   
   
       6 . The method according to  claim 25 , wherein the amount (in weight %) of Cu is in a range of 1.5 to 2.1. 
   
   
       7 . The method according to  claim 25 , wherein the amount (in weight %) of Cu is in a range of 1.5 to 2.0. 
   
   
       8 . The method according to  claim 25 , wherein the amount (in weight %) of Zr is in a range of 0.05 to 0.15. 
   
   
       9 . The method according to  claim 25 , 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 . The method according to  claim 25 , wherein the amount (in weight %) of Zn is in a range of 6.1 to 8.3. 
   
   
       11 . The method according to  claim 25 , 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 . The method according to  claim 25 , 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 . The method according to  claim 25 , wherein the amount (in weight %) of Fe is less than 0.12. 
   
   
       14 . The method according to  claim 25 , wherein the amount (in weight %) of Si is less than 0.12. 
   
   
       15 - 16 . (canceled) 
   
   
       17 . The method according to  claim 25 , wherein the product is a plate product. 
   
   
       18 . The method according to  claim 25 , wherein the product is a plate product having a thickness is a range of 15 to 45 mm. 
   
   
       19 - 24 . (canceled) 
   
   
       25 . A method for producing a wrought high-strength Al—Zn alloy product 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.   
   
   
       26 . The method according to  claim 25  wherein the worked and solution heat-treated product is artificially aged, and wherein the aging 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. 
   
   
       27 . The method according to in  claim 26 , wherein the worked and solution heat-treated product is artificially aged, and wherein the aging 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. 
   
   
       28 . The method according to  claim 25 , wherein the worked and solution heat-treated product is artificially aged, and wherein the aging 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 210° C. for 4 to 12 hours. 
   
   
       29 . The method according to  claim 25 , characterized by artificially aging the worked and solution heat-treated product with a two-step aging procedure to a T79 or T76 temper. 
   
   
       30 . The method according to  claim 25 , 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. 
   
   
       31 . The method according to  claim 30 , wherein the worked product is a plate product and the plate product is a thin aircraft member. 
   
   
       32 . The method according to  claim 30 , wherein the worked product is a plate product and the plate product is an elongate structural shape member of an aircraft. 
   
   
       33 . The method according to  claim 30 , wherein the worked product is a plate product and the plate product is an upper-wing member of an aircraft. 
   
   
       34 . The method according to  claim 30 , wherein the worked product is a plate product and the plate product is a thin skin member of an upper-wing of an aircraft. 
   
   
       35 . The method according to  claim 30 , wherein the worked product is a plate product and the plate product is stringer of an aircraft. 
   
   
       36 . The method according to  claim 30 , wherein the worked product is a plate product and the plate product is stringer of an upper-wing of an aircraft. 
   
   
       37 . The method according to  claim 25 , wherein the amount (in weight %) of Zn is in a range of 6.1 to 8.3 and Mn is lower than 0.02. 
   
   
       38 . The method according to  claim 25 , wherein the amount (in weight %) of Zn is in a range of 6.1 to 7.0 and Mn is lower than 0.05. 
   
   
       39 . The method according to  claim 25 , wherein the amount (in weight %) of Zn is in a range of 6.1 to 7.0 and Mn is lower than 0.02.