Method for manufacturing a 7xxx aluminum alloy plate and 7xxx aluminum alloy plate

Abstract

The present invention relates to plates with a thickness comprised between 6 and 25 mm made of an aluminum alloy with a composition, in weight %, Zn: 4.5-7.0; Mg: 1.2-3.5; Cu: 1.0-3.0; at least one element selected from among Cr: 0.04-0.35, Zr: 0.04-0.15 and Mn 0.04-0.5; Ti<0.25; Fe<0.6; Si<0.5; other elements <0.05 each and <0.15 in total, the remainder being aluminum and a manufacturing method thereof. The plates according to the invention are particularly useful as precision plates, in particular to make machine bases, reference plates, transport tables, assembly jigs, robot arms. The plates according to the invention have an improved dimensional stability in particular during the machining steps, while having sufficient static mechanical properties, and a good anodization capability.

1 . A method for manufacturing a plate made of an aluminum alloy with a final thickness comprised between 6 and 25 mm, said method comprising successively,
 a) casting a rolling slab comprising an aluminum alloy with the composition, in weight %, Zn: 4.5-7.0; Mg: 1.2-3.5; Cu: 1.0-3.0; at least one element selected from among Cr: 0.04-0.35, Zr: 0.04-0.15 and Mn 0.04-0.5; Ti<0.25; Fe<0.6; Si<0.5; other elements <0.05 each and <0.15 in total, the remainder being aluminum,   b) homogenizing said rolling slab,   c) hot-rolling said rolling slab to obtain a plate with a thickness at least equal to 8 mm, the reduction rate upon the last hot-rolling pass being at most 20%,   d) carrying out an intermediate heat treatment lasting at least 1 hour at a temperature between 100° C. and 350° C.,   e) cold-rolling the heat treated plate with a reduction rate of 10% to 33%,   f) carrying out a solution heat treatment of the cold-rolled plate and quenching it,   g) stress relieving said solution heat treated and quenched plate by controlled stretching with a permanent elongation of 1 to 5%,   h) carrying out an aging of the solution heat treated, quenched and optionally stress relieved plate,   i) optionally, machining said aged plate to obtain a plate with a final thickness at least equal to 6 mm.   
     
     
         2 . The method according to  claim 1 , wherein the homogenization temperature is comprised between 450° C. and 500° C. 
     
     
         3 . The method according to  claim 1 , wherein the hot-rolling exit temperature is at most 355° C. 
     
     
         4 . The method according to  claim 1 , wherein the heat treatment of d is carried out after hot-rolling is carried out at a temperature comprised between 130° C. and 320° C., and optionally at a temperature comprised between 200° C. and 300° C. 
     
     
         5 . The method according to  claim 1 , wherein reduction rate by cold-rolling is 20% to 30%. 
     
     
         6 . The method according to  claim 1 , wherein rolling speed during the last hot-rolling pass is at most 1,000 mm/s, optionally at most 900 mm/s and preferaMy optionally at most 800 mm/s. 
     
     
         7 . A plate with a thickness comprised between 6 and 25 mm with a composition comprising, in weight %, Zn: 4.5-7.0; Mg: 1.2-3.5; Cu: 1.0-3.0; at least one element selected from among Cr: 0.04-0.35, Zr: 0.04-0.15 and Mn 0.04-0.5; Ti<0.25; Fe<0.6; Si<0.5; other elements <0.05 each and <0.15 in total, the remainder being aluminum, obtainable by the method according to  claim 1 . 
     
     
         8 . The plate according to  claim 7  having a tensile yield strength Rp0.2LT of at least 450 MPa, optionally at least 460 MPa and optionally at least 480 MPa, and/or an ultimate tensile strength RmLT of at least 500 MPa, optionally at least 520 MPa and optionally at least 540 MPa and/or an elongation at break A % of at least 6%, optionally at least 8% and optionally at least 10%. 
     
     
         9 . The plate according to  claim 7 , wherein a product of the maximum deflection deviation in the L and LT directions multiplied by the final thickness is at most 3 and optionally at most 2, considered deflection deviations, in absolute value, to obtain a maximum value being, on one hand, a deflection deviation between deflection measured for a bar with the dimension 400 mm×30 mm×thickness at the exit of cold-rolling and the deflection measured for said bar after machining M of thickness thereof and, on another hand, a deflection deviation between deflection measured for a previous bar and a deflection measured for said previous bar after an additional machining of M of a thickness thereof, all deflection measurements being performed with the bar placed on two supports distant apart by 390 mm and the deflections being expressed in mm, all measurements being performed before final optional machining. 
     
     
         10 . The plate according to  claim 7 , wherein the ratio of the sum of the planar compression texture volumetric fraction to the sum of the shear texture volumetric fraction is comprised between 0.5 and 1.5 and optionally between 0.6 and 1.3 between the mid-thickness and the surface after machining if machining has been carried out or 1.5 mm under the surface if no machining has been carried out. 
     
     
         11 . A product comprising a plate according to  claim 7  as a precision plate, optionally to make one or more machine bases, reference plates, transport tables, assembly jigs, robot arms or parts with a complex shape with material removal by machining.