Method of making 6XXX aluminium sheets

Patent metadata

Field	Value
Publication number	US-11535919-B2
Application number	US-201716316640-A
Country	US
Kind code	B2
Filing date	Jul 12, 2017
Priority date	Jul 14, 2016
Publication date	Dec 27, 2022
Grant date	Dec 27, 2022

Abstract

The invention concerns a method for producing a 6xxx series aluminium sheet comprising the steps of homogenizing an ingot made from a 6XXX series aluminum alloy; cooling the homogenized ingot with a cooling rate in a range of from 150° C./h to 2000° C./h directly to the hot rolling starting temperature; hot rolling the ingot to a hot rolling final thickness and coiling at the hot rolling final thickness with such conditions that at least 50% recrystallization is obtained; cold rolling to obtain a cold rolled sheet. The method of the invention is particularly helpful to make sheets for the automotive industry which combine high tensile yield strength and good formability properties suitable for cold stamping operations, as well as high surface quality and high corrosion resistance with a high productivity.

First claim

The invention claimed is:

1. A method for producing a 6xxx series aluminium sheet comprising
homogenizing an ingot made from a 6XXX series aluminum alloy comprising 0.3-1.5 wt. % of Si, 0.3-1.5 wt. % of Mg and 1.5 wt. % or less of Cu, Mn 0.03-0.5 wt. % and/or Cr 0.01-0.4 wt. %, Fe 0.03 to 0.4 wt. %, Ti up to 0.1 wt %, rest aluminium and unavoidable impurities up to 0.05 wt. % each and 0.15 wt. % total,
wherein the aluminum alloy ingot comprises at least 250 mm in thickness, from 1000 to 2000 mm in width, and from 2000 to 8000 mm in length; a top surface, a bottom surface, and four side surfaces, wherein the top and bottom surfaces have a larger surface area than the side surfaces; and a head and a foot corresponding to extremities in a longitudinal direction,
cooling the homogenized ingot with a cooling rate at mid-thickness and/or at quarter thickness in a range from 150° C./h to 2000° C./h directly to a hot rolling starting temperature, wherein a thermal differential of less than 40° C. over the entire ingot, which is cooled from the homogenization temperature, is obtained when hot rolling is started,
hot rolling the ingot to a hot rolling final thickness and coiling at the hot rolling final thickness with such conditions that at least 50% recrystallization is obtained, wherein the hot rolling starting temperature is between 350° C. and 450° C. and a hot rolling exit temperature is at least 310° C. and wherein the thickness reduction during a last hot rolling pass is at least 25%,
cold rolling to obtain a cold rolled sheet.

2. A method according to claim 1 wherein the cold rolling reduction is at least 65%.

3. A method according to claim 1 wherein the cold rolled sheet is further solution heat treated and quenched in a continuous annealing line.

4. A method according to claim 3 wherein the continuous annealing line is operated in such a way that the equivalent holding time at 540° C., t eq 540° , is less than 35 sec, the equivalent holding time being calculated according to the equation

t
eq

540
⁢
°

=

∫

time
⁢

⁢
spent
⁢

⁢
in
⁢

⁢
furnace

⁢

dt
.
exp

⁢

⌈

-

Q
R

·

(

1

T

°
⁢

⁢

C
.

⁡

(
t
)

+
273

-

1

540
+
273

)

⌉

with Q an activation energy of 146 kJ/mol and R=8.314 J/mol.

5. A method according to claim 3 wherein after solution heat treatment and quench the sheet is aged to a T4 temper, cut and formed to final shape, painted and bake hardened.

6. A method according to claim 1 wherein the cooling is carried out in at least two phases: a first spraying phase in which the ingot is cooled in a chamber comprising ramps of nozzles for spraying cooling liquid or spray under pressure, divided into upper and lower parts of said chamber, so as to spray the top and bottom surfaces of said ingot and a complementary phase of thermal equalization in still air, in a tunnel with interior reflective walls, lasting from 2 to 30 minutes depending on the ingot format and the cooling.

7. A method according to claim 6 wherein the spraying and thermal equalization phases are repeated, and the ingot has a thickness of at least 400 mm and a cooling of more than 80° C.

8. A method according to claim 6 , wherein the cooling liquid, including that in a spray, is water, and optionally deionized water.

9. A method according to claim 1 , wherein the head and the foot of the ingot are less cooled than the rest of the ingot, so as to maintain a hot head and foot.

10. A method according to claim 6 , wherein cooling of the head and the foot is modulated by turning the ramps of nozzles on or off.

11. A method according to claim 9 , wherein the cooling of the head and the foot is modulated by the presence of screens.

12. A method according to claim 6 , wherein the spraying phase and not the thermal equalization phase is repeated, and the head and the foot of the ingot are cooled differently from the rest of the ingot in at least one of the spray phases.

13. A method according to claim 6 , wherein the longitudinal thermal uniformity of the ingot is improved by relative movement of the ingot in relation to the ramps of nozzles: the ingot passes or moves with a reciprocating movement facing the ramps of nozzles or vice versa.

14. A method according to claim 13 , wherein the ingot moves horizontally in the spray phase and its speed is greater than, or equal to 20 mm/s, or 1.2 m/min.

15. A method according to claim 6 , wherein transverse thermal uniformity of the ingot is ensured by modulating spraying in the ingot width by switching the nozzles or spray nozzles on or off, or screening said spraying.

16. The method according to claim 4 wherein the equivalent holding time at 540° C., t eq 540° , is less than 25 seconds.

17. A method according to claim 1 , wherein the hot rolling exit temperature is at least 330° C.

18. A method according to claim

Assignees

• Constellium Neuf Brisach
• Uacj Corp

Inventors

• Guiglionda Gilles
• Boissonnet Laurent
• Carisey Sylvain
• Yamamoto Yusuke
• Shinzato Yoshifumi
• Asano Mineo
• Betsuki Yoichiro

Classifications

• C22C21/02

  with silicon as the next major constituent · CPC title

• C22C21/18

  with zinc · CPC title

• C22F1/05 Primary

  of alloys of the Al-Si-Mg type, i.e. containing silicon and magnesium in approximately equal proportions · CPC title

• B21B1/36

  by cold-rolling · CPC title

• C22C21/08

  with silicon · CPC title