Method for producing a high damage tolerant aluminium alloy

1 . Method for producing a high damage tolerant aluminium alloy rolled product a high toughness and an improved fatigue crack growth resistance, comprising the steps of

a.) casting an ingot having a composition selected from the group comprising of AA2000, AA5000, AA6000, and AA7000-series alloys;

b.) homogenising and/or pre-heating the ingot after casting;

c.) hot rolling the ingot into a hot rolled product and optionally cold rolling the hot rolled product into a cold rolled product, wherein the hot rolled product leaves the hot rolling mill at an hot-mill exit temperature (T Exit ) and cooling the hot rolled product from said T Exit to 150° C. or lower with a controlled cooling cycle with a cooling rate falling within the range defined by:

T ( t )=50−(50 −T exit ) e αt

and wherein t(t) is the temperature (° C.) as function in time (hrs), t is the time (hours) and α is in the range of −0.09±0.05 (hrs −1 ).

2 . Method according to claim 1 , wherein α is in the range of −0.09±0.03 (hrs −1 ).

3 . Method according to claim 1 , wherein the hot rolled product is subjected to the controlled cooling cycle, thereby maintaining an elevated temperature for a predetermined time.

4 . Method according to claim 1 , wherein the hot rolled product is subjected to the controlled cooling cycle by coiling the hot rolled product alloy after hot rolling.

5 . Method according to claim 1 , wherein the hot rolled product is subjected to the controlled cooling cycle by coiling the hot rolled product alloy after hot rolling and hot rolling and cold rolling are in the same direction.

6 . Method according to claim 1 , wherein the hot rolled product is subjected to the controlled cooling cycle by coiling the hot rolled product alloy after hot rolling and hot rolling and cold rolling are in dissimilar directions.

7 . Method according to claim 1 , wherein the hot rolled product is subjected to the controlled cooling cycle by continuously moving the rolled product through a furnace after hot rolling, wherein said furnace is adjustable to apply heat to the rolled alloy product while passing to a cold rolling station or a coiling station.

8 . Method according to claim 1 , wherein the hot rolled product is subjected to the controlled cooling cycle by coiling the rolled alloy product after hot rolling in a furnace wherein said furnace is adjustable to control the cooling rate of the alloy product while coiling.

9 . Method according to claim 1 , wherein the hot rolled product has a gauge in a range of less than 12 mm while leaving the hot rolling mill at the hot-mill exit temperature.

10 . Method according to claim 9 , wherein the hot rolled product has a gauge in a range of 1 to 10 mm.

11 . Method according to claim 9 , wherein the hot rolled product has a gauge in a range of 4 to 8 mm.

12 . Method according to claim 7 , wherein the hot rolled product is cold rolled to a total cold roll reduction of 40 to 70%.

13 . Method according to claim 1 , wherein the method further includes one or more of the following process steps:

d.) solution heat treating of the hot rolled product after being subjected to the controlled cooling cycle or of the cold rolled product;

e.) quenching the solution heat treated alloy product;

f.) optionally stretching or compressing of the quenched alloy product;

g.) optionally ageing the quenched and optionally stretched or compressed alloy product to achieve a desired temper.

14 . Method according to claim 13 , comprising said stretching or compressing of the quenched alloy product.

15 . Method according to claim 1 , wherein the average cooling rate in the controlled cooling cycle is in a range of 12 to 20° C./hour.

16 . Method according to claim 1 , wherein the cast ingot comprises the following composition (in weight percent):

Si

0.6-1.3

Cu

0.04-1.1 

Mn

0.1-0.9

Mg

0.4-1.3

Fe

0.01-0.3 

Zr

<0.25

Cr

<0.25

Zn

<0.6

Ti

<0.15

V

<0.25

Hf

<0.25,

other elements each less than 0.05 and less than 0.20 in total, balance aluminium.

17 . Method according to claim 1 , wherein the cast ingot comprises an alloy within the compositional range of AA6013 or AA6056.

18 . Method according to claim 1 , wherein the cast ingot comprises the following composition (in weight percent):

Cu

3.8-5.2

Mg

0.2-1.6

Cr

<0.25

Zr

<0.25

Mn

≦0.50 and Mn: >0

Fe

≦0.15

Si

≦0.15,

other elements each less than 0.05 and less than 0.15 in total, balance aluminium.

19 . Method according to claim 18 , wherein the cast alloy comprises at least one member of the group consisting of Mn-containing dispersoids and Zr-containing dispersoids.

20 . Method according to claim 18 , wherein Zr of the cast ingot is in the range of 0.06-0.18 and Mn of the cast ingot is in the range of>0.15 to 0.50.

21 . Method according to claim 1 , wherein the casting an ingot comprising the following composition (in weight percent):

Zn

5.0-9.5

Cu

1.0-3.0

Mg

1.0-3.0

Mn

<0.35

Zr

<0.25

Cr

<0.25

Fe

<0.25

Si

<0.25

Sc

<0.35

Ti

<0.10

Hf and/or V

<0.25,

other elements each less than 0.05 and less than 0.15 in total, balance aluminium.

22 . Method according to claim 21 , wherein Zr of the cast ingot is in the range of 0.06-0.16.

23 . Method according to claim 1 , wherein the cast ingot comprises an alloy within the compositional range selected from the group consisting of AA7040, AA7050 and AA7x75.

24 . An aluminium alloy sheet or plate product having a high toughness and an improved fatigue crack growth resistance made of an alloy produced according to the method of claim 1 .

25 . A rolled alloy sheet product according to claim 24 , wherein said product is a structural member of an aircraft or an automobile.

26 . A rolled alloy sheet product according to claim 24 , wherein said product is a fuselage skin of an aircraft or a vehicle component part.

27 . A rolled alloy product according to claim 24 , wherein the rolled alloy product has a final gauge in the range of 2 to 7 mm.