A 6xxx alloy for high strength extruded products with high processability

Abstract

The invention concerns an improved alloy to obtain AA6xxx alloy extrusions with high strength, typically having an ultimate tensile strength higher than 390 MPa, and high processability, in particular with a high productivity, as well as high surface quality and high corrosion resistance. In particular, the alloy of the invention contains, in wt. %, Si 0.6-0.9, Mg 0.55-0.76, Cu 0.65-0.9, Mn 0.4-0.7, Cr 0.05-0.2, Zr 0.10-0.19, Fe 0.05-0.5, Zn≤1.0, V≤0.10, Ti≤0.10, other elements <0.05 each and <0.15 total, rest aluminium. The extruded profiles of the invention are advantageously used as automotive components such as crash boxes, a bumpers, a side impact beams or side sills.

1 . An extruded profile comprising an Al—Mg—Si alloy containing, in wt. %,
 Si 0.6-0.9, 
 Mg 0.55-0.76, 
 Cu 0.65-0.9, 
 Mn 0.4-0.7, 
 Cr 0.05-0.2, 
 Zr 0.10-0.19, 
 Fe 0.05-0.5, 
 Zn≤1.0, 
 V≤0.10, 
 Ti≤0.10, 
 other elements <0.05 each and <0.15 total, rest aluminium. 
 
     
     
         2 . An extruded profile according to  claim 1  wherein the Cu content is from 0.75 to 0.85 wt. %. 
     
     
         3 . An extruded profile according to  claim 1  wherein the microstructure is essentially unrecrystallized. 
     
     
         4 . An extruded profile according to claim  4  wherein peripheral coarse grain is at most 400 μm thick per wall side. 
     
     
         5 . An extruded profile according to  claim 1  wherein solidus temperature of the alloy is from 580° C. to 610° C., optionally from 585° C. to 600° C. and more optionally from 588° C. to 595° C. and even more optionally from 589° C. to 594 C. 
     
     
         6 . An extruded profile according to  claim 1  wherein the flow stress measured at 480° C. and a strain rate of 0.14 s −1  is at most 35 MPa and optionally at most 32 MPa. 
     
     
         7 . An extruded profile according to  claim 1  wherein the extruded profile is in a T6 temper and has an ultimate tensile strength in a longitudinal direction of at least 390 MPa and optionally of at least 400 MPa. 
     
     
         8 . A method to make an extruded profile according to  claim 1  comprising successively steps of
 (a) Casting a billet containing, in wt. %,
 Si 0.6-0.9, 
 Mg 0.55-0.76, 
 Cu 0.65-0.9, 
 Mn 0.4-0.7, 
 Cr 0.05-0.2, 
 Zr 0.10-0.19, 
 Fe 0.05-0.5, 
 Zn≤1.0, 
 V≤0.10, 
 Ti≤0.10, 
 other elements <0.05 each and <0.15 total, rest aluminium 
 
 (b) Homogenizing the billet, 
 (c) Cooling the homogenized billet to room temperature, 
 (d) Solution heat treating the homogenized billet at a temperature from 500° C. to 560° C. for a duration from 150 s to 500 s and quenching to a temperature from 300° C. to 500° C. or reheating the homogenized billet directly and without solutionising to a temperature from 300° C. to 500° C., 
 (e) Extruding at an extrusion rate from 5 m/mn to 15 m/mn said heat treated and quenched or reheated billet to obtain an extruded profile, 
 (f) Quenching, stretching and aging said extruded profile. 
 
     
     
         9 . The method to make an extruded profile according to  claim 8  wherein homogenization temperature is from 530° C. to 580° C. and wherein extrusion rate is at least 7 m/mn. 
     
     
         10 . A product comprising an extruded profile according to  claim 1  as an automotive component optionally a crash box, a bumper, a side impact beam or a side sill.