Metallurgical product and structure member for aircraft made of Al-Zn-Cu-Mg alloy

Abstract

The present invention relates to a work-hardened product, and particularly a rolled, extruded and/or forged product made of an alloy with composition (% by weight): Zn 6.7-7.3% Cu 1.9-2.5% Mg 1.0-2.0% Zr 0.04-0.15% Fe ≦0.15 Si ≦0.15 other elements ≦0.05 each and ≦0.15 total, remainder aluminium and wherein Mg/Cu<1. The product is preferable treated by solution heat treatment, quenching, cold working and artificial aging. Cold working may be achieved by controlled tension and/or cold transformation, for example rolling or drawing. The product may be used, for example, as an aircraft structural member.

1 . A work-hardened product comprising an alloy having a composition (% by weight)of: 
 Zn 6.7-7.3% Cu 1.9-2.5% Mg 1.0-2.0%    Zr 0.04-0.15% Fe ≦0.15 Si ≦0.15    other elements ≦0.05 each and ≦0.15 total, remainder aluminium, wherein Mg/Cu<1, 
 said product being treated by solution heat treatment, quenching, cold working and artificial aging.  
   
     
     
         2 . A product according to  claim 1 , wherein Zr≦0.12%.  
     
     
         3 . A product according to  claim 1 , wherein Zr content is from about 0.07 to about 0.09%.  
     
     
         4 . A product according to  claim 1 , wherein the Cu content is from about 2.0 to about 2.3%.  
     
     
         5 . A product according to  claim 1 , wherein the Mg content is from about 1.5 to about 1.8%.  
     
     
         6 . A product according to  claim 1 , wherein Mg/Cu≦0.80.  
     
     
         7 . A product according to  claim 1  having a thickness of at most about 20 mm, wherein 
 (a) K app(L-T)  (measured at ambient temperature on a C(T) type test piece with W=127 mm and B=5.5 mm)>100 MPa{square root}m    (b) R p0.2(L) >500 MPa.    
     
     
         8 . A product according to  claim 1 , wherein R m(L) >500 MPa.  
     
     
         9 . A product according to  claim 1 , wherein R P0.2(L) >about 460 Mpa.  
     
     
         10 . A plate with a thickness of at most about 20 mm comprising a product according to  claim 2 , having at least one selected from the group consisting of: 
 (a) R m(L) >520 MPa and R P0.2(LT) >515 MPa;    (b) R P0.2(L) >500 MPa and R P0.2(LT) >480 MPa; and    (c) R P0.2(L) >500 MPa and K app(TL) >100 Mpa{square root}m (measured at ambient temperature on a C(T) type test piece with W=127 mm and B=5.5 mm).    
     
     
         11 . A plate according to  claim 10 , wherein da/dn in the T-L direction is at least about 28×10−4 mm/cycles, determined at ΔK=30 Mpa{square root}m.  
     
     
         12 . A sheet or plate with a thickness from about 1 to about 10 mm comprising a product according to  claim 1 , wherein K C(T-L) , measured on a test piece with W=760 mm, is at least about 130 Mpa{square root}m, and/or wherein K C(L-T) , measured on a test piece with W=760 mm, is at least about 160 Mpa{square root}m.  
     
     
         13 . A plate according to  claim 10 , wherein said plate has been hot rolled only.  
     
     
         14 . A plate with thickness of at least about 10 mm comprising a product according to  claim 2 , wherein said plate has been heat treated for at least 4 hours at a temperature of from about 470 to about 480° C.  
     
     
         15 . A plate with thickness of at most about 10 mm comprising a product according to  claim 2  wherein said plate has been solution heat treated for at least 1 hour at a temperature of from about 470 to about 480° C.  
     
     
         16 . A plate with a thickness of at least about 20 mm comprising a product according to  claim 2  having at least two characteristics selected from the group consisting of: 
 (a) R m(L) >540 MPa;    (b) R P0.2(L) >535 MPa;    (c) K app(LT) >100 Mpa{square root}m (measured at ambient temperature on a C(T) type test piece with W=127 mm and B=7.6 mm);    (d) ΔK at a crack propagation rate of 2.54 μm/cycle>28 Mpa{square root}m; and    (e) K IC (L-T)>28 MPa{square root}m.    
     
     
         17 . A plate with a thickness of at least 20 mm comprising a product according to  claim 2 , having at least two characteristics selected from the group consisting of: 
 (a) yield strength R p0.2(L)  equal to at least 520 MPa;    (b) K app(L-T)  (measured at ambient temperature according to ASTM 561 on a C(T) type test piece with W=406 mm and thickness B=6.35 mm) equal to at least 130 Mpa{square root}m; and    (c) K C(L-T)  (measured at ambient temperature on a C(T) type test piece with W=406 mm and thickness B=6.35 mm) equal to at least 185 Mpa{square root}m.    
     
     
         18 . A plate comprising a product of  claim 1  that is clad on at least one face thereof.  
     
     
         19 . A product according to  claim 1  wherein said product has been produced from a liquid metal to which a refining agent containing titanium and carbon has been added, such that the carbon quantity added to said liquid metal is from about 0.4 to about 3 g/t of carbon, and such that the total content of Ti in the product is from about 50 to about 500 ppm (by weight).  
     
     
         20 . A structural member suitable for aircraft comprising at least one product according to  claim 1 .  
     
     
         21 . An integral structure suitable for aircraft comprising at least one product according to  claim 1 .  
     
     
         22 . A fuselage skin comprising a rolled product comprising a product according to  claim 2  and having a thickness of at most about 10 mm.  
     
     
         23 . A method for machining aircraft structural members comprising using a product according to  claim 1  having a thickness of at least about 40 mm.  
     
     
         24 . A method for making aircraft stiffeners or frames comprising using a product according to  claim 1  with a thickness of at least about 60 mm.  
     
     
         25 . A product wherein the value of K app(L-T)  measured according to ASTM 561 on a C(T) type test piece with W=406 mm and thickness B=6.35 mm when measured at −54° C. is not more than about 2% less than said value at ambient temperature.  
     
     
         26 . A product of  claim 25 , wherein said value at −54 C is the same or slightly greater than said value at ambient temperature.  
     
     
         27 . A product with a yield strength R P0.2(L)  at mid-thickness equal to at least about 540 MPa and a toughness K app(LT)  measured on an M(T) type specimen with a width W of 16 inches (about 406 mm) equal to at least about 140 Mpa{square root}m, said product comprising a structural member for aircraft and having a weight at least 10% less than a structural member with the same yield strength and toughness comprising a 7475 alloy.  
     
     
         28 . A product of  claim 27  wherein said product comprises an alloy having a composition (% by weight) of: 
 Zn 6.7-7.3% Cu 1.9-2.5% Mg 1.0-2.0%    Zr 0.04-0.15% Fe ≦0.15 Si ≦0.15    other elements ≦0.05 each and ≦0.15 total, remainder aluminium, wherein Mg/Cu<1.    
     
     
         29 . An integral structure comprising a plate according to  claim 16 .  
     
     
         30 . An integral structure of  claim 29  that is at least about 40 mm in thickness.  
     
     
         31 . An integral structure comprising a plate according to  claim 17 .  
     
     
         32 . An integral structure according to  claim 31  that is at least about 40 mm in thickness.  
     
     
         33 . A structural member comprising a product of  claim 2 .  
     
     
         34 . A structural member of  claim 33  that is at least about 10 mm in thickness.  
     
     
         35 . A structural member comprising a product of  claim 3 .  
     
     
         36 . A structural member of  claim 35  that is at least about 10 mm in thickness.  
     
     
         37 . A structural member comprising a plate according to  claim 14.