Method for manufacturing an aluminum-copper-lithium alloy having improved compressive strength and improved toughness

Abstract

The invention relates to a manufacturing method in which an alloy is prepared that comprises 3.5 to 4.7 wt % of Cu; 0.6 to 1.2 wt % of Li; 0.2 to 0.8 wt % of Mg; 0.1 to 0.2 wt % of Zr; 0.0 to 0.3 wt % of Ag; 0.0 to 0.8 wt % of Zn; 0.0 to 0.5 wt % of Mn; at most 0.20 wt % of Fe+Si; optionally an element selected from Cr, Sc, Hf and V, the amount of said element, if selected, being from 0.05 to 0.3 wt % for Cr and for Sc, 0.05 to 0.5 wt % for Hf and for V; the other elements being at most 0.05 wt % each and 0.15 wt % in total, a refiner is introduced, the alloy is cast in a crude form, homogenized, hot-worked, solution heat-treated, quenched, cold-worked, and tempered, in which the refiner contains particles of TiC and/or the cold working is between 8 and 16%. The products obtained by the method according to the invention have an advantageous compromise between mechanical strength and toughness.

1 . A method for manufacturing a product based on an aluminum alloy wherein, successively,
 a) a liquid metal bath based on aluminum is prepared comprising 3.5 to 4.7 wt % of Cu; 0.6 to 1.2 wt % of Li; 0.2 to 0.8 wt % of Mg; 0.1 to 0.2 wt % of Zr; 0.0 to 0.3 wt % of Ag; 0.0 to 0.8 wt % of Zn; 0.0 to 0.5 wt % of Mn; at most 0.20 wt % of Fe+Si; optionally an element selected from Cr, Sc, Hf and V, the amount of said element, if selected, being from 0.05 to 0.3 wt % for Cr and for Sc, 0.05 to 0.5 wt % for Hf and for V; other elements at most 0.05 wt % each and 0.15 wt % in total and the remainder being aluminum;   b) a refiner is introduced into said bath so that the Ti content is comprised between 0.01 to 0.15 wt %;   c) a crude form is cast from said liquid metal bath;   d) said crude form is homogenized at a temperature comprised between 450° C. and 550° C. and optionally between 480° C. and 530° C. for a period comprised between 5 and 60 hours;   e) said homogenized crude form is hot-worked, optionally by rolling;   f) the hot-worked product is solution heat-treated between 490° C. and 530° C. for 15 min to 8 hours and said solution heat-treated product is quenched;   g) said product is cold-worked with a cold working of 2 to 16%;   h) aging is carried out wherein said product thus cold-worked reaches a temperature comprised between 130° C. and 170° C. and optionally between 140° C. and 160° C. for 5 to 100 hours and optionally 10 to 70 hours;   wherein said refiner contains particles of the TiC type and/or said cold working is of 8 to 16%.   
     
     
         2 . The method according to  claim 1 , wherein the refiner containing particles of the TiC type is introduced in a form and an amount such that an amount of TiC identical to that added with a refiner AT3C0.15 at a rate of 2 to 5 kg/t of aluminum alloy is added. 
     
     
         3 . The method according to  claim 1  wherein the cold working of g comprises:
 g1) said product is cold rolled with a thickness reduction rate comprised between 8 to 12%; 
 g2) said product is tensioned in a controlled manner with a permanent set comprised between 0.5 and 4%. 
 
     
     
         4 . The method according to  claim 1 , wherein the aging is carried out at a temperature comprised between 140 and 155° C., optionally between 145 and 150° C., optionally for 18 to 22 hours. 
     
     
         5 . The method according to  claim 1 , wherein the copper content is comprised between 4.0 and 4.6 wt % and optionally between 4.1 and 4.5 wt %. 
     
     
         6 . The method according to  claim 1 , wherein the manganese content is comprised between 0.05 and 0.4 wt %. 
     
     
         7 . The method according to  claim 1  wherein the Ag content is of 0.1 to 0.27 wt % and/or the Zn content is of 0.2 to 0.40 wt %. 
     
     
         8 . A product based on an aluminum alloy that can be obtained by the method according to  claim 1 . 
     
     
         9 . The product according to  claim 8  comprising a rolled product with a thickness comprised between 8 and 50 mm and having, at mid-thickness,
     K   app ( L−T )≥−0.5 Rc   p0.2 ( L )+375,
 
   optionally  K   app ( L−T )≥−0.5 Rc   p0.2 ( L )+386
 
 with Kapp (L−T) expressed in MPa√m, the value of the apparent stress intensity factor at rupture defined according to standard ASTM E561 (2015) measured on CCT test specimens of width W=406 mm and thickness B=6.35 mm, and 
 Rc p0.2 (L), expressed in MPa, the compressive yield strength measured at 0.2% compression according to standard ASTM E9 (2018). 
 
     
     
         10 . The product according to  claim 8  comprising a rolled product with a thickness comprised between 8 and 50 mm and having, at mid-thickness,
     K   app ( L−T )≥−0.5 Rc   p0.2 ( L )+386,
 
   optionally  K   app ( L−T )≥−0.5 Rc   p0.2 ( L )+391, and
 
     R   p0.2 ( L )>600 MPa, optionally 615 MPa, 
 with Kapp (L−T) expressed in MPa√m, the value of the apparent stress intensity factor at rupture defined according to standard ASTM E561 (2015) measured on CCT test specimens of width W=406 mm and thickness B=6.35 mm, and 
 Rc p0.2 (L), expressed in MPa, the compressive yield strength measured at 0.2% compression according to standard ASTM E9 (2018), and R p0.2  (L) the conventional yield strength at 0.2% elongation measured in the longitudinal direction of the product, determined by a tensile test according to standard NF EN ISO 6892-1 (2016). 
 
     
     
         11 . An aircraft structure element, optionally an aircraft upper wing skin element, comprising a product according to  claim 9 .