EP3652363B1

EP3652363B1 - An aluminium alloy rolled product with intense iridiscent colors

Info

Publication number: EP3652363B1
Application number: EP18735324.8A
Authority: EP
Inventors: Jean-Sylvestre Safrany; David FAIHY
Original assignee: Constellium Rolled Products Singen GmbH and Co KG
Current assignee: Constellium Rolled Products Singen GmbH and Co KG
Priority date: 2017-07-10
Filing date: 2018-07-05
Publication date: 2021-06-23
Anticipated expiration: 2038-07-05
Also published as: FR3068712A1; WO2019011778A1; EP3652363A1; FR3068712B1; ES2882886T3

Description

FIELD OF THE INVENTION

The present invention relates to decorative aluminium rolled products having iridescent colors.

BACKGROUND OF THE INVENTION

Various aluminium alloys are used in the form of rolled products for decorative applications such as cosmetic packaging, automotive trims (exterior and interior), interior design, sound system and consumer electronics.
Obtain iridescent colors on aluminium rolled products is known. By iridescent colors it is meant that the color changes as a function of the incident angle. In particular, it may be obtained on anodized aluminium having porous anodic oxide films obtained in various electrolytes (sulfuric, phosphoric, oxalic acid etc.). As shown in Figure 1, porous anodic oxide films consist of two layers, a porous thick outer layer 22 and an inner layer which is dense and dielectrically compact called the barrier layer 21. The iridescent phenomenon is due to interference between the light reflected on the oxide surface and the light reflected on a metal/oxide interface. At different incident angles V, as illustrated in Figure 1, different wavelengths of light have either positive or negative interference resulting in different colors being perceived.
Iridiscent colors may be observed on porous anodic oxide films. In the article "Optical properties and color generation mechanism of porous anodic alumina films" Applied Surface Science 258 (2011) 1826-1830 examples are provided of iridescent anodic aluminum oxide films obtained on high purity aluminum foils by phosphoric acid anodizing. The phenomenon appears to be enhanced if the porous anodic oxide film is colored.
In the article "Synthesis and properties of iridescent Zn-containing anodic aluminum oxide films" - Thin Solid Films 586 (2015) 8- 12, examples are provided of iridescent anodic aluminum oxide films obtained on high purity aluminum foils by phosphoric acid anodizing followed by Zn deposition.
In the article "Synthesis of iridescent Ni-containing anodic aluminum oxide films by anodization in oxalic acid" - Optical Materials 52 (2016) 107 - 110, examples are provided of iridescent anodic aluminum oxide films obtained by acid anodizing followed by Ni electro deposition.
The patent application WO2017/013607 relates to a structural colouration method for colouring an aluminium substrate, exemplified by alloy 6061, which comprises forming a nano structure of one-dimensional photonic crystals by means of a process of periodic current pulse anodisation, the colour obtained depending on the application time of the maximum and/or minimum current density of the pulse, and the colour varying with the angle of observation.
In the article "Electrocolouring of anodized aluminium with copper:effect of porous and barrier oxide film thickness", G. Pastore et al Thin Solid Films, 173 (1989) 299-308, is described the effect of the thickness of both porous and compact films of aluminium, exemplified by alloy 6063, anodized in 15% H₂SO₄ on the electrocolouring process using copper sulphate and magnesium sulfate solutions.
In the article "Colour simulation and prediction of complex nano-structured metal oxide films Test case : Analysis and modeling of electro-coloured anodized aluminium", I. De Graeve et al. Surface and Coatings Technology 205 (2011) 4349-4354, is described an optical modeling procedure to predict and model the colour of electro-coloured anodized aluminum exemplified by an aluminum AA5005 having 0.7 wt.% Fe and 0.3 wt.% Si.
Patent application US2016/0362808 describes a formed aluminum article, exemplified by alloys 6061 and 6063, in which pores formed by anodic oxidation are filled with a pigment, the formed aluminum article having an adequately colored film.
The colors can be adjusted by modifying the anodizing and coloring parameters, but for typical anodizing quality, e.g. high purity foils such as those described in the mentioned articles or more generally on 1XXX series alloys, the overall coloring effect remains light.
There is thus a need to obtain decorative aluminium rolled products with strong iridescent colors.

SUMMARY OF THE INVENTION

An object of the invention is an anodized decorative rolled product made of an aluminum alloy consisting of, in weight %,

Mg : 0 - 1.5,
Mn : 0 - 1.5,
With Mg + Mn : 0.5 - 3
and wherein either Mn : 0.8 - 1.5 or Mg : 0.5 - 1.1 and Mn ≤ 0.2,
Si : ≤ 0.6,
Fe : ≤ 0.8,
Ti : ≤ 0.1,
Cu : ≤ 0.3,
Cr : ≤ 0.1,
Zn : ≤ 0.25,
Zr : ≤ 0.1,
other elements ≤ 0.05 each and ≤ 0.15 in total, remainder aluminium,
wherein the rolled product has a porous anodic oxide film which is colored electrochemically or chemically and wherein the color of the decorative sheet is different if viewed at an incidence angle 0° and at an incidence angle of 45° and wherein the porous anodic oxide film is covered by a sol-gel coating preferably comprising silicon.

Another object of the invention is a method to make an anodized decorative rolled product according to the invention comprising the steps of

casting an aluminum alloy according to the invention to form an ingot;
reheating and/or homogenizing the ingot preferably at a temperature from 460°C to 560°C,
hot rolling the ingot to a hot rolling final thickness preferably at a temperature from 350 to 500°C,
cold rolling to obtain a cold rolled product, with a preferred final thickness from 0.2 to 2 mm and preferably from 0.5 to 0.8 mm,
optionally annealing said cold rolled product preferably at a temperature from 200 to 300 °C,
cleaning said cold rolled product, preferably with a solvent or an aqueous cleaner containing surfactants,
optionally providing a matt or bright aspect for example by satin matt etching or by chemical/electrochemical brightening,
anodizing said cold rolled product in sulfuric acid, phosphoric acid or oxalic acid or a combination thereof to obtain a porous anodic oxide film,
coloring said porous anodic oxide film by electrochemical deposition preferably of at least one of Zn, Ni, Sn, Co, Cu, Ag of or chemical deposition preferably of at least one dye among an azo dye, an anthraquinone dye, an indigo dye,
rinsing with deionized water,
optionally sealing the porous anodic oxide film by hydrothermal sealing, cold sealing or a combination thereof,
drying,
coating the porous anodic oxide film by depositing a sol-gel precursor followed by evaporation and/or curing.

DESCRIPTION OF THE FIGURES

Figure 1 : Interference between the light reflected on the oxide surface and the light reflected on a metal/oxide interface, for an anodic porous alumina on an aluminium surface.

DESCRIPTION OF THE INVENTION

All aluminium alloys referred to in the following are designated using the rules and designations defined by the Aluminum Association in Registration Record Series that it publishes regularly, unless mentioned otherwise.
Unless otherwise indicated, all the indications relating to the chemical composition of the alloys are expressed as a mass percentage by weight based on the total weight of the alloy. In the formula Mg + Cu, Mg and Cu means the percentage by weight of Mg and Cu, respectively.
Metallurgical tempers referred to are designated using the European standard EN-515.
The inventors have found that by using alloys having a specific composition, and in particular including additions of Mg and/or Mn it is possible to obtain decorative aluminium rolled products with strong iridescent colors
According to the invention, an anodized decorative rolled product with strong iridescent colors can be obtained with rolled product made of an aluminum alloy consisting of, in weight %,

The presence of Mn and/or Mg containing precipitates in the alloy surprisingly enhances the colors and iridescent properties.
Presence of Si further improves the strength of colors in some instances. Advantageously the Si content is at least 0.03 wt.%. Excessive Si content can however be detrimental to formability. Preferably the Si content is at most 0.3 wt.% and preferably at most 0.25 wt.% and more preferably at most 0.2 wt.%.
Similarly presence of Fe further improves the strength of colors in some instances. Advantageously the Fe content is at least 0.02 wt.%. Excessive Fe content can however be detrimental to formability. Preferably the Fe content is at most 0.5 wt.%, more preferably at most 0.4 wt.% and preferentially at most 0.2 wt.%. Preferably Fe is at most 0.5 wt.% and Si is at most 0.3 wt.%. The other elements which have a content of ≤ 0.05 wt.% each and ≤ 0.15 wt.% in total, are undesirable impurities.
In a first embodiment, the alloy contains from 0.8 to 1.5 wt.% Mn and is preferably an alloy from the 3XXX series. Preferred alloys in this first embodiment are AA3103, AA3104 and AA3005. Preferably in the first embodiment the Mg content is at most 1.3 wt.% and preferably at most 0.6 wt.%
In a second embodiment the Mn content is at most 0.2 wt.% and the Mg content is from 0.5 to 1.1 wt.%. In this second embodiment the alloy is preferably an alloy from the 5XXX series. This second embodiment is advantageously also combined with a Si content of at most 0.2 wt.%, preferably at most 0.1 wt.% and most preferably at most 0.04 wt.%. This second embodiment is advantageously also combined with a Fe content of at most 0.2 wt.%, preferably at most 0.1 wt.% and most preferably at most 0.06 wt.%.Preferred alloys in this second embodiment are AA5005, AA5505 and AA5657.
The method to make an anodized decorative rolled product according according to the invention comprises the steps of

casting an aluminum alloy according to the invention to form an ingot;
reheating and/or homogenizing the ingot preferably at a temperature from 460°C to 560°C,
hot rolling the ingot to a hot rolling final thickness preferably at a temperature from 350 to 500°C,
cold rolling to obtain a cold rolled product, with a preferred final thickness from 0.2 to 2 mm and preferably from 0.5 to 0.8 mm,
optionally annealing said cold rolled product preferably at a temperature from 200 to 300 °C,
cleaning said cold rolled product, preferably with a solvent or an aqueous cleaner containing surfactants,
optionally providing a matt or bright aspect for example by satin matt etching or by chemical/electrochemical brightening,
anodizing said cold rolled product in sulfuric acid, phosphoric acid or oxalic acid or a combination thereof to obtain a porous anodic oxide film,
coloring said porous anodic oxide film by electrochemical deposition preferably of at least one of Zn, Ni, Sn, Co, Cu, Ag of or chemical deposition preferably of at least one dye among an azo dye, an anthraquinone dye, an indigo dye,
rinsing with deionized water,
optionally sealing said porous anodic oxide film by hydrothermal sealing, cold sealing or a combination thereof,
drying,
coating the porous anodic oxide film by depositing a sol-gel precursor followed by evaporation and/or curing.

Typical surfactants are anionic such as carboxylates or sulphonates, nonionic such as ethoxylated aliphatic alcohols, cationic such as quaternary ammonium salts or amphoteric such as aliphatic aminocarboxylic acid salts.
The porous outer layer obtained from acid anodizing can be schematically represented as a closed-packed array of hexagonally arranged cells containing pores in each cell-center. Figure 1 illustrates a cross section of a porous anodic oxide film 2 on aluminium an aluminium substrate 1, comprising a barrier layer 21 and a porous outer layer 22. The porous anodic oxide film is characterized by given parameters such as a pore diameter, interpore distance (cell diameter) of the porous outer layer and the barrier layer thickness. The porous anodic oxide film of the products according to the invention exhibit a barrier layer with a thickness advantageously from 15 to 25 nm, in order to obtain the desired iridiscent colors. The porous anodic oxide film total thickness is advantageously between 1 and 10 µm.
Typically, a sulfuric anodizing can be achieved at 1-1,5A/dm² at 20°C, providing an approximately 21 nm thick barrier layer, the anodizing time being adjusted to vary the coloring effect,
The coloring dyestuff concentration may vary from 0.1 to 10g/L, depending on the color and the required darkness. The temperature is usually in the range of 50 to 60°C, with some exceptions working at lower temperature.
According to the invention the porous anodic oxide film is coated by depositing a sol-gel precursor followed by evaporation and/or curing to obtain a sol-gel coating. The present inventors observed that surprisingly the sol-gel coating does not alter the iridescent appearance, probably because of its specific optical properties. The sol-gel coating protects the porous anodic film from scratches, fingerprints, and other surface deffects. On the contrary, conventional coatings such as clear lacquer does not allow not to keep the iridescent aspect.
Preferably the sol-gel precursor is made from a mixture of a polysiloxane, preferably prepared from an alcoholic solution of silane, more preferably from an alcoholic solution of an alkoxysilane, and an aqueous solution of colloidal silica. The sol-gel precursor is advantageously prepared from two solutions A and B, solution A being an alcoholic solution of one or more alkoxysilanes, the alcohol used as solvent being methanol, ethanol, propanol, preferably isopropanol, butanol or a combination thereof, the alkoxysilanes being described by the general formula XnSi(OR)4-n wherein "R" is a simple alkyl, preferably chosen in the group consisting of methyl, ethyl, propyl and butyl and "X" is also an alkyl, preferably selected from the group consisting of methyl, ethyl, propyl and butyl; solution B being a solution of colloidal silica dissolved in water. Advantageously the alkoxysilanes belong to the group comprising tetramethoxysilane (TMOS), tetraethoxysilane (TEOS) and methyl trimethoxysilane (MTMOS). Preferably solution A contains 25 - 35 wt% TEOS and 15 - 25 wt% MTMOS, both dissolved in 40 - 60 wt% isopropyl alcohol. Advantageously solution B is set with an acid, preferably with nitric acid (HNO3), to a pH value between 2.0 and 4, preferably between 2.5 and 3.0 and more preferably close to 2.7. Advantgeously the alkali content of the silica is less than 0.04 wt % Na₂O.
Preferably the deposition of the sol-gel precursor is carried out by immersion. Advantageoulsy the sol-gel coating thickness is comprised between 2 and 4 µm. Preferably, the sol-gel coating contains a small quantity of organic compounds, for example the carbon content of the coating as measured by XPS (X-Ray Photoelectron Spectrometry) is less than 10 atomic % as measured by concentration profile through the sol-gel coating. Preferably curing of the sol-gel is done at a temperature comprised between 150 and 250 °C during 30 to 60 seconds.
The product of the invention is particularly useful for decorative applications such as cosmetic packaging, automotive trims (exterior and interior), interior design, sound system and consumer electronics.

EXAMPLE

Example 1 (reference example)

In this example, rolled products made of several alloys have been tested for color anodizing.

The composition of the alloys is provided in Table 1

Table 1, Typical composition of alloys in wt.%

alloy	Si	Fe	Cu	Mn	Mg	Cr	Zn	Ti	Zr	Mg+Mn
1070	0,01	0,12	0,002	0,002	0,002	0,002	0,002	0,002	0,002	0,004
5657	0,04	0,06	0,04	0,002	0,7	0,002	0,002	0,002	0,002	0,702
5505	0,04	0,03	0,002	0,002	0,8	0,002	0,002	0,002	0,002	0,802
3103	0,20	0,5	0,002	1,1	0,002	0,002	0,002	0,002	0,002	1,102
3104	0,21	0,35	0,2	0,9	1,3	0,008	0,002	0,01	0,002	2,2

The products received a surface treatment as follows :

Solvent cleaning with Methyl-Ethyl Ketone on flat samples
Deionized water rinse
Anodizing with sulphuric acid 180g/L, at 20°C, for 1 to 2 min under a DC current of 1 A/dm²
Deionized water rinse
Electrolytic coloring : with nickel sulphate 30g/L, boric acid 30g/L, ammonium sulphate 15g/L, 35°C, 2 min 19V AC current or chemical coloring with an azo dye chromium complex : Sanodal® Black 2LW (1g/L), with an azo dye copper complex : Sanodure® Fast Gold L (3g/L), and with an anthraquinone dye :Sanodye® Blue 2LW (3g/L) at 60°C during 2 min,
Deionized water rinse
drying

The resulting samples were observed at different incident angles. The intensity of colors was classified through comparison with reference samples and scaled from 1 : light to 3 : strong.

The results are provided in Table 2

Table 2 - Results obtained

Alloy	Anodizing duration (min)	coloring	Color (intensity) at incident angle
Alloy	Anodizing duration (min)	coloring	0°	45°	90°
1070	1	electroly tic	Green (1)	Pink(1)	Green-Blue (1)
1070	2	Chemical (black)	Pink (1)	Blue-Green (1)	uncolore d
5657	2	Chemical (black)	Pink (2)	Blue-Green (2)	uncolore d
5505	2	Chemical (gold)	Gold-green (2)	Gold-pink (2)	Gold (2)
3103	2	Chemical (blue)	Blue (2)	Pink (2)	Blue (2)
3103	1,5	Chemical (blue)	Pink (2)	Blue (2)	Pink (2)
3104	1	electroly tic	Green (3)	pink (3)	Green-Blue (3)
3104	2	Chemical (black)	Pink (3)	Blue-green (3)	Pink (2)

Intensity : 1 : light, 2 : medium, 3 : strong

Coloring with alloys according to the invention enables obtention of strong iridescent colors, ranging from 2 to 3.

Example 2

The sample of example 1 made of alloy 5657 is protected by a sol-gel coating.
The sol-gel solution applied by immersion consists of the mixture of a solution A and a solution B.
Anhydrous solution A comprises a mixture of unhydrolyzed siloxanes and alcohols:

50% by weight of isopropanol
30% by weight of tetraethylorthosilicate (TEOS)
20% by weight of trimethoxymethylsilane (MTMOS)

The pH of solution B is modified to reach 2.5 by addition of acid such as, for example, HNO3. The silica must have the lowest possible alkaline content, preferably less than 0.04 mass% of Na2O.
Solution A is mixed with solution B in the presence of nitric acid with continuous stirring and leads to a hydrolysis and condensation reaction bringing the mixture to a gel state. Solutions A and B are mixed with a weight ratio of preferably 7: 3. The mixture is preferably maintained at a pH value of between 2 and 4, preferably 2.5 to 3.0, and most preferably 2.7. The pH value is corrected by addition of acid, preferably nitric acid.
After mixing solutions A and B for 6 hours, the resulting solution is filtered. The filtration may, for example, be carried out using polypropylene filters with a mesh size of 1 micron. Before use, the solution is left standing for 12 to 22 hours before being applied to the substrate to form the protective deposit.
The baking of the deposit is carried out at a temperature of 150 to 250 ° C for 30s to 60s. The thickness of the deposit is preferably 2 to 4 µm and contains only very few organic compounds (less than 10 at%, measured by depth profile in XPS).
The strong iridescent coloring of the alloy according to the invention is not modified by the sol-gel coating, which is suprising because irridescence is based on interference phenomena and the addition of a thin coating is expected to affect coloring. Moreover the surface is well protected mechanically by the sol-gel coating.

Claims

An anodized decorative rolled product made of an aluminum alloy consisting of, in weight %,
Mg : 0 - 1.5,
Mn : 0 - 1.5,
with Mg + Mn : 0.5 - 3, and wherein
either Mn : 0.8 - 1.5
or Mg : 0.5 - 1.1 and Mn ≤ 0.2,
Si : ≤ 0.6,
Fe : ≤ 0.8,
Ti : ≤ 0.1,
Cu : ≤ 0.3,
Cr : ≤ 0.1,
Zn : ≤ 0.25,
Zr : ≤ 0.1,
other elements ≤ 0.05 each and ≤ 0.15 in total, remainder aluminium,
wherein the rolled product has a porous anodic oxide film which is colored electrochemically or chemically and wherein the color of the decorative sheet is different if viewed at an incidence angle 0° and at an incidence angle of 45° and characterized in that the porous anodic oxide film is covered by a sol-gel coating preferably comprising silicon.
A product according to claim 1 wherein
Fe is at most 0.5 wt.% and Si is at most 0.3 wt.%.
A product according to claim 1 or claim 2 wherein
Mn is at most 0.2 wt, Si is at most 0.1 wt.% and Fe is at most 0.2 wt.%.
A product according to claim 1 or claim 2 wherein
Mn : 0.8 - 1.5 wt.% and wherein the Mg content is at most 1.3 wt.% and preferably at most 0.6 wt.%.
A product according to anyone of claims 1 to 4 wherein the Si content is at least 0.03 wt.%.
A product according to anyone of claims 1 to 5 wherein the Fe content is at least 0.02 wt.%.
A product according to any of claims 1 to 6 wherein the barrier layer of the porous anodic oxide film has a thickness from 15 to 25 nm.
A product according to any of claims 1 to 7 wherein the porous anodic oxide film comprises at least one of Zn, Ni, Sn, Co, Cu, Ag.
A product according to any of claims 1 to 7 wherein the porous anodic oxide film comprises at least one dye among a azo dye, an anthraquinone dye, an indigo dye.
A method to make an anodized decorative rolled product according to anyone of claims 1 to 9 comprising the steps of
- casting an aluminum alloy according to anyone of claims 1 to 6 to form an ingot;

- reheating and/or homogenizing the ingot preferably at a temperature from 460°C to 560°C,

- hot rolling the ingot to a hot rolling final thickness preferably at a temperature from 350 to 500°C,

- cold rolling to obtain a cold rolled product, with a preferred final thickness from 0.2 to 2 mm and preferably from 0.5 to 0.8 mm,

- optionally annealing said cold rolled product preferably at a temperature from 200 to 300 °C,

- cleaning said cold rolled product, preferably with a solvent or an aqueous cleaner containing surfactants,

- optionally providing a matt or bright aspect for example by satin matt etching or by chemical/electrochemical brightening,

- anodizing said cold rolled product in sulfuric acid, phosphoric acid or oxalic acid or a combination thereof to obtain a porous anodic oxide film,

- coloring said porous anodic oxide film by electrochemical deposition preferably of at least one of Zn, Ni, Sn, Co, Cu, Ag of or chemical deposition preferably of at least one dye among an azo dye, an anthraquinone dye, an indigo dye,

- rinsing with deionized water,

- optionally sealing the porous anodic oxide film by hydrothermal sealing, cold sealing or a combination thereof,

- drying,

- coating the porous anodic oxide film by depositing a sol-gel precursor followed by evaporation and/or curing.
A method according to claim 10 wherein the sol-gel precursor is made from a mixture of a polysiloxane, preferably prepared from an alcoholic solution of silane, more preferably from an alcoholic solution of an alkoxysilane, and an aqueous solution of colloidal silica.
A method according to claim 11 wherein the sol-gel precursor is prepared from two solutions A and B, solution A being an alcoholic solution of one or more alkoxysilanes, the alcohol used as solvent being methanol, ethanol, propanol, preferably isopropanol, butanol or a combination thereof, the alkoxysilanes being described by the general formula XnSi(OR)4-n wherein "R" is a simple alkyl, preferably chosen in the group consisting of methyl, ethyl, propyl and butyl and "X" is also an alkyl, preferably selected from the group consisting of methyl, ethyl, propyl and butyl;
solution B being a solution of colloidal silica dissolved in water.
A method according to claim 12 wherein said alkoxysilanes belong to the group comprising tetramethoxysilane (TMOS), tetraethoxysilane (TEOS) and methyl trimethoxysilane (MTMOS).
A method according to claim 13, wherein the solution A contains 25 - 35 wt% TEOS and 15 - 25 wt% MTMOS, both dissolved in 40 - 60 wt% isopropyl alcohol.