Strip made of 6xxx alloy and manufacturing process

Abstract

The invention relates to the field of 6XXX series aluminum alloy strips and to a process for manufacturing same. These strops are particularly useful for producing bodywork parts of motor vehicles on account of the compromise they offer between corrosion resistance and formability.

1 . An aluminum alloy strip with a composition of, in % by weight:
 Si: 1.2-1.5,   Fe: ≤0.25,   Cu: ≤0.05,   Mn: 50.15,   Mg: 0.20-0.45,   Cr: 0.002-0.09   Ni: ≤0.15   Zn: ≤0.15   Ti: ≤0.15   Zr: ≤0.15,   unavoidable elements and impurities in a maximum of 0.05% each, together 0.15% maximum, remainder aluminum.   
     
     
         2 . The aluminum alloy strip according to  claim 1  wherein Si: 1.25-1.45, optionally 1.25-1.40. 
     
     
         3 . The aluminum alloy strip according to  claim 1  wherein Fe: 0.10-0.20, or 0.10-0.15 or 0.15-0.20. 
     
     
         4 . The aluminum alloy strip according to  claim 1  wherein Mn: 0.05-0.10. 
     
     
         5 . The aluminum alloy strip according to  claim 1  wherein Mg: is less than or equal to 0.39%, optionally 0.35%, optionally 0.34%, mere optionally 0.33%. 
     
     
         6 . The aluminum alloy strip according to  claim 1  wherein Cu: maximum 0.03, or Cu 0.01-0.04 or Cu 0.02-0.04. 
     
     
         7 . The aluminum alloy strip according to  claim 1  wherein Ti≤0.10, or ≤0.06, or 0.02-0.08. 
     
     
         8 . The aluminum alloy strip according to  claim 1  wherein Cr 0.005-0.03 or Cr 0.01-0.05. 
     
     
         9 . The aluminum alloy strip according to  claim 1  wherein Ni 0.002-0.01 or Ni 0.005-0.02. 
     
     
         10 . The aluminum alloy strip according to  claim 1  wherein excess of Si content over Mg content is at least 0.95% by weight, optionally at least 1.00% by weight. 
     
     
         11 . The aluminum alloy strip according to  claim 1  wherein the strip of thickness between 0.7 and 1.0 mm in T4 temper has a minimum LDH of at least 26.0 mm, wherein the strip of thickness between 1.1 and 1.5 mm T4 temper has a minimum LDH of at least 26.5 mm. 
     
     
         12 . The aluminum alloy strip according to  claim 1 , wherein the average length of the filiform corrosion filaments, wherein according to EN 3665, in an unsanded zone is less than 2 mm, optionally less than 1 mm, after the strip has been pre-deformed by 2% in the rolling transverse direction, then painted, then paint bake at 180° C. for 20 minutes, or that the average length of the filiform corrosion filaments, characterized according to 3665, in an unsanded zone is less than 1 mm, optionally less than 0.8 mm, after the strip has been pre-deformed by 2% in a rolling transverse direction, then painted, then paint bake at 180° C. for 20 minutes. 
     
     
         13 . A method for manufacturing an aluminum alloy strip according to  claim 1  comprising:
 a. Casting a slab, optionally by semi-continuous vertical casting, 
 b. Homogenizing the slab optionally at a temperature between 500° C. and 600° C., optionally between 540 and 580° C. and optionally between 1 hour and 12 hours, optionally comprising a second stage between 420° C. and 550° C. with a maximum duration of 4 hours, 
 c. Cooling the slab to the hot rolling start temperature between 350° C. and 550° C. at a cooling rate optionally greater than 150° C./h or cooling the slab to room temperature and then reheating the slab to said hot rolling start temperature, 
 d. Hot rolling the slab into a strip, with the hot rolling end temperature between 250° C. and 450° C., 
 e. Cold rolling the strip, optionally in two parts separated by intermediate annealing, said annealing being optionally carried out on the strip rolled up into a coil, 
 f. Solution heat treating the strip, optionally between 500° C. and 600° C. for 10 to 60 s, followed by quenching, 
 g. Pre-ageing the strip by coiling the slab to a temperature of between 50 and 100° C., followed by cooling to room temperature, 
 h. Naturally ageing the strip at room temperature between 72 hours and 6 months. 
 
     
     
         14 . A car body part obtained by
 a. Supplying an aluminum alloy strip according to  claim 1 ,   b. Stamping   c. Painting   d. Paint baking between 15 and 60 minutes at a temperature of between 120 and 200° C.,   wherein average length of filiform corrosion filaments, after a corrosion test according to EN 3665, in an sanded zone is less than 2 mm, optionally less than 1 mm, or that the average length of filiform corrosion filaments in an unsanded zone is less than 1 mm, optionally less than 0.8 mm.