Manufacturing process for obtaining high strength extruded products made from 6xxx aluminium alloys

Abstract

A manufacturing process for obtaining extruded products made from a 6xxx aluminium alloy, wherein the said manufacturing process comprises following steps: a) homogenizing a billet cast from said aluminium alloy; b) heating the said homogenised cast billet; c) extruding the said billet through a die to form at least a solid or hollow extruded product; d) quenching the extruded product down to room temperature; e) optionally stretching the extruded product to obtain a plastic deformation typically between 0.5% and 5%; f) ageing the extruded product without applying on the extruded product any separate post-extrusion solution heat treatment between steps d) and f). characterised in that: i) the heating step b) is a solution heat treatment where: b1) the cast billet is heated to a temperature between Ts-15° C. and Ts, wherein Ts is the solidus temperature of the said aluminium alloy; b2) the billet is cooled until billet mean temperature reaches a value between 400° C. and 480° C. while ensuring billet surface never goes below a temperature substantially close to 400° C.; ii) the billet thus cooled is immediately extruded (step c)), i.e. a few tens seconds after the end of step b2).

1 . A wrought product extruded from a 6xxx aluminium alloy, wherein said 6xxx aluminium alloy comprises Si: 0.3-1.7 wt. %; Mg: 0.1-1.4 wt. %; Mn: 0.1-1.4%, and at least one dispersoid element comprising Cr (0.05-0.4 wt. %) or Zr (0.05-0.25 wt %), the rest being aluminium and inevitable impurities. 
     
     
         2 . The wrought product according to  claim 1 , wherein said 6xxx aluminium alloy further comprises at least one of Cu: 0.01-1.5 wt. % and Zn: 0.01-0.7%. 
     
     
         3 . The wrought product according to  claim 1 , wherein Cu content is between 0.4 and 1.5 wt. %. 
     
     
         4 . The wrought product according to  claim 1 , having a thickness lower than 6 mm, wherein said 6xxx aluminium alloy is aged to a T6 temper to obtain an ultimate tensile strength higher than 380 MPa, optionally higher than 400 MPa, optionally higher than 420 MPa. 
     
     
         5 . The wrought product according to  claim 1 , wherein
 1.2 wt. %≤Mg2Si≤1.6 wt. % and   0.2 wt. %≤Si—Mg/1.73−(Fe+Mn)/3≤0.7 wt. %.   
     
     
         6 . The wrought product according to  claim 4 , wherein the thickness is lower than 3 mm. 
     
     
         7 . The wrought product according to  claim 1 , that is a hollow extrudate. 
     
     
         8 . The wrought product according to  claim 1 , wherein the 6xxx aluminium alloy is one of the following alloys: AA6056, AA6156, Cu-doped AA6056, Cu-doped AA6156, Cu-doped AA6082 or, optionally, Cu-doped AA6182. 
     
     
         9 . The wrought product according to  claim 1 , wherein a manufacturing process of the wrought product comprises:
 a) homogenizing a billet cast from said aluminium alloy and then cooling the billet down to room temperature;   b) heating the homogenized cast billet;   c) extruding said billet through a die to form at least a solid or hollow extruded product;   d) quenching with a water quench the extruded product down to room temperature; and   f) ageing the extruded product without applying on the extruded product any separate post-extrusion solution heat treatment;   wherein:   i) the heating b) is a solution heat treatment where:   b1) the cast billet is heated to a temperature between Ts-15° C. and Ts, wherein Ts is the solidus temperature of said aluminium alloy and is at least 575° C.;   b2) the billet is cooled until billet mean temperature reaches a value between 400° C. and 480° C. while ensuring billet surface never goes below 400° C.;   ii) the billet thus cooled is immediately extruded in c after the end of b2.   
     
     
         10 . The wrought product according to  claim 9 , wherein the ageing treatment is a one- or multiple-step heat treatment at a temperature between 150° C. and 200° C. for a prescribed period of time, defined to obtain maximum ultimate strength. 
     
     
         11 . The wrought product according to  claim 9 , wherein said cast billet is homogenized in a) at a temperature between 80° C. and 150° C. lower than solidus. 
     
     
         12 . The wrought product according to  claim 9 , further comprising, between d) and f):
 e) stretching the extruded product to obtain a plastic deformation.   
     
     
         13 . The wrought product according to  claim 12 , wherein the plastic deformation is between 0.5% and 5%. 
     
     
         14 . The wrought product according to  claim 11 , wherein said cast billet is homogenized in a) at a temperature between 450° C.-500° C. 
     
     
         15 . The wrought product according to  claim 4 , wherein the 6xxx aluminium alloy comprises Cu, and the extruded product has an ultimate tensile strength higher than 400 MPa. 
     
     
         16 . The wrought product according to  claim 4 , wherein the extruded product has an ultimate tensile strength higher than 410 MPa.