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1. (WO2017093304) ALUMINIUM EXTRUSION ALLOY SUITABLE FOR ETCHED AND ANODIZED COMPONENTS
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Aluminium extrusion alloy suitable for etched and anodized components

The present application claims the benefit of priority of Norwegian patent application NO20151653, filed on December 2, 2015 with the Norwegian Patent Office with the title "Aluminium extrusion alloy suitable for etched and anodized components", the entire content of which is incorporated herein by reference.

The present invention relates to an aluminum alloy suitable for etched and anodized components. More particularly the present invention relates mainly to extrusion alloys of the types MgSi, 6060 and 6063 which after being extruded to any wide variety of forms for different applications such as house buildings and other building

applications, is subjected to etching and subsequent anodizing.

Due to environmental issues, it is foreseen that there will be an increased demand for re-melting post consumed aluminium products in the future. This may lead to somewhat higher levels of trace elements, like Zn in the re-melted metal, i.e. an enrichment over time.

Customers sometimes explicitly ask for recirculated aluminium, likely due to concern for the environment and reduced carbon footprint. It is therefore a prerequisite for metal suppliers to be able to handle such requests.

During normal alkaline etching prior to anodizing, it is experienced that some grains can be etched deeper than others, called "preferential grain etching" or "grainy" or "spangle appearance". Further, the gloss that is created by etching usually increases with increased Zn content in alloy.

Due to the etching of such materials, the Zn-content in the etching bath may be enriched and influence on the etching response as well. This may be avoided by using additives that precipitate the accumulated Zn-ions. There are several suppliers, promoting different proprietary additives (different amounts and types of chemicals) and they may give varying results.

Preferential grain etching (PGE) is caused by Zn in the alloy and/or in the etching bath as indicated above. Thus, it has been found that when alloys containing zinc with an amount in excess of 0.03 wt% are etched in a solution alkaline etching bath, these alloys tend to yield a "grainy" surface appearance.

Reliable measurement of free Zn-ions in the etching bath is normally done by ICP (Inductively Coupled Plasma Mass Spectrometry) which is a time consuming procedure and which has to be carried out by specialists. An easy and reliable measuring technique has not been established so far. An alternative remedy is to increase the use of additives on a regular basis for instance by adding sufficient Na2S in the etching tanks one day and then the etching tank is ready for use the next day or day thereafter.

An alternative method is to carry out mechanical pretreatment of the profile surface (shot blasting) such that the necessary time in the etch tank is reduced and the risk of preferential grain etching is reduced.

Still another alternative method that may be possible is the use of acid etch instead of alkaline etching bath. However, the use of acid in etch baths is encumbered with high risk of hazardous impact on the environments and persons involved in the etching bath operation and is not permitted in most western countries.

From US 3,594,133 is known an etched article being made from an Al-Mg-Si alloy where the Cu/Zn ratio is required to be 1 :1 on a weight basis ratio when the zinc content is in the range 0.03 - 0.10 wt% and 2:1 when the zinc content is above 0.10 wt%. Tests performed by the inventors of the present invention has proved, however, that the high content of copper does not prevent formation of PGE. Besides, the patent suggests high Cu content, which is harmful in relation to the corrosion resistance of the alloy and high Zn content which increases the Zn content of the etching bath and which in turn causes increased PGE.

The 6060 alloys contain according to the international AA standard 0.30 - 0.6 wt% Si, 0.10 -0.30 wt% Fe, max 0.10 wt% Cu, max 0.10 wt% Mn, 0.35 - 0.6 wt% Mg, max 0.05 wt% Cr, max 0.15 wt% Zn and max 0.10 wt% Ti, others each max 0.05 wt% and others total max 0.15 wt%. The 6063 alloys contains according to the AA standard on the other hand 0.20 - 0.6 wt% Si, max 0.35 wt% Fe, max 0.10 wt% Cu, max 0.10 wt% Mn, 0.45 - 0.9 wt% Mg, max 0.10 wt% Cr, max 0.10 wt% Zn and max 0.10 wt% Ti, others each max 0.05 wt% and others total max 0.15 wt%.

With the present invention is provided a selection alloy solution where the Zn and Cu alloying elements of the 6060 and 6063 types of alloys, based on extensive testing in many experiments, are controlled to obtain the desired and consistent, optimal gloss and PGE appearance of such alloys.

The invention provides an alloy according to claim 1 . Further embodiments of the invention are described in the dependent claims, which describe preferred subranges that result in alloys with favorable properties.

The Cu and Zn ranges in the claims are described by an area/polygon in the Cu-Zn diagram. The claimed ranges lie within the area that is obtained by drawing straight lines between the points in ascending order (e.g. a straight line from a1 to a2, a straight line from a2 to a3, etc.) and further a straight line between the last and the first point (e.g. a straight line from a6 to a1 ). The points and lines itself limit the area and are not a part of the claimed area. That is, the alloys according to the invention comprise at least a small amount of Zn and a small amount of Cu. Further, if for example an area is partially defined by a straight line drawn from a point

corresponding to 0.025 wt-% Cu and 0.025 wt-% Zn to a point corresponding to 0.05 wt-% Cu and 0.05 wt-% Zn, said area does not include alloys having a ratio of Cu/Zn equal to 1 , but for example only includes alloys having a ratio of Cu/Zn below 1 . When a dependent claims refers to points (e.g. a1 and a5) mentioned in a claim to which said dependent claim refers (e.g. a1 , a2, a3, a4, a5), these points are redefined by the dependent claim and the relevant area is formed by these redefined points (e.g. a1 and a5) together with the points mentioned in the claim from which said dependent claim is dependent and which are not redefined (e.g. a2, a3, a4). When a dependent claim introduces a new set of points (points with a new index letter such as b1 , b2, b3, b4), said claim is directed to said smaller/narrower area defined by said new set of points (such as b1 , b2, b3, b4) unless it is indicated otherwise. Figure 28 shows exemplary Cu-Zn ranges according to the invention.

A particularly robust alloy resistant to PGE and having good properties may be obtained when the Cu-Zn content of an alloy according to claim 1 is held within the composition window defined by points f1 , f2, f3 and f4 in a Cu-Zn diagram, wherein f1 corresponds to 0.017 wt-% Cu and 0.025 wt-% Zn, f2 corresponds to 0.04 wt-% Cu

and 0.07 wt-%Zn, f3 corresponds to 0.03 wt-% Cu and 0.07 wt-% Zn, and f4 corresponds to 0.007 wt-% Cu and 0.025 wt-% Zn. As is described herein (see e.g. also Fig. 26), good properties with respect to PGE have also been obtained when the alloy according to claim 1 comprises Cu and Zn in the composition window defined by points f1 , f2, f3 and f4 as described in the sentence before, but has a minimum Zn concentration of more than 0.04 wt-% Zn. In other words, good properties with respect to PGE have been found when the Cu and Zn content of an alloy according to claim 1 is within the composition window defined by points f1 *, f2*, f3* and f4* in the Cu-Zn diagram, wherein f1 * corresponds to (approximately) 0.025 wt-% Cu and 0.04 wt-% Zn, f2* (equal to f2) corresponds to 0.04 wt-% Cu and 0.07 wt-% Zn, f3* (equal to f3) corresponds to 0.03 wt-% Cu and 0.07 wt-% Zn, and f4* corresponds to (approximately) 0.015 wt-% Cu and 0.04 wt-% Zn.

The invention will be further described in the following by way of example and with reference to the figures where;

Fig. 1 shows a photomicrograph of a 6063 aluminum alloy where preferential grain etching (PGE) is caused by Zn in the alloy ("The surface treatment and finishing of aluminum and its alloys", S. Wernick et al, Fifth Edition, Finishers Publishers Ltd.),

Figs. 2-8 show each SEM micrographs of a first series of extruded and anodized

6xxx alloys together with a vertical bar chart depicting the concentrations of Fe, Zn and Cu as well as images of anodised samples.

Figs. 9-12 show each SEM micrographs of a second series of extruded and

anodized 6xxx alloys together with a vertical bar chart representing the concentrations of Zn and Cu as well as images of anodised samples,

Fig. 13 shows a summary of developed or avoided PGE on extruded and

anodized 6xxx alloys with different concentrations of Cu and Zn based on Experiments 1 and 2.

Fig. 14a shows a table summarizing conditions and results of Experiments 1 , 2 and 3.

Fig. 14b shows alloy compositions of samples used in Experiments 1 , 2 and 3. Figs. 15-26 show detailed results of trials conducted for Experiments 1 , 2 and 3.

Fig. 27 shows a relationship between temper condition and preferential grain etching.

Fig. 28 shows a summary of claimed composition ranges.

As stated above the present invention relates to aluminum alloys and particularly aluminium extrusion alloys of the types containing Magnesium and Silicon, 6060 and 6063 which after being extruded to any wide variety of forms for different applications such as house buildings and other building applications, is subjected to etching and subsequent anodizing. During normal alkaline etching prior to anodizing, it is experienced that some grains can be etched deeper than others, called "preferential grain etching" (PGE) or "grainy" or "spangle appearance". Fig. 1 shows a micrograph where such etching is depicted.

Extensive testing has been performed to arrive at an alloy composition where the Zn and Cu alloying elements are controlled to obtain the desired gloss and PGE. The alloy according to an embodiment of the invention may contain as follows in wt%: Si: 0.20 - 0.90, Mg: 0.30 - 0.90, Fe: 0.10 - 0.40, Mn: max 0.20, Zn: 0.025 - 0.10, Cu: 0.005 - 0.05, Ti: max 0.10, Cr: max 0.10, where the relation between Cu and Zn is controlled to avoid preferential grain etching and the ratio of Cu/Zn is below 1 , including others or incidental impurities each in the amount of 0.05 wt% max, the total of others and impurities being in the amount of 0.15 wt% max and balance Al.

In this respect, the invention may according to a first exemplary aspect provide an aluminium alloy suitable for etched and anodized components, in particular aluminum extrusion alloys of the types containing Magnesium and Silicon, which after being extruded to any wide variety of forms for different applications such as house buildings and other building applications is subjected to etching in a conventional alkaline etching bath and subsequent anodizing, consisting of in wt%: Si: 0.20 - 0.90, Mg: 0.30 - 0.90, Fe: 0.10 - 0.40, Mn: max 0.20, Zn: 0.025 - 0.10, Cu: 0.005 -0.05,Ti: max 0.10, Cr: max 0.10, where the relation between Cu and Zn is controlled to avoid preferential grain etching and the ratio of Cu/Zn is below 1 , including others or incidental impurities each in the amount of 0.05 wt% max, the total of others and impurities being in the amount of 0.15 wt% max and balance Al.

According to a second exemplary aspect, the alloy according to the first aspect may be a 6060 or 6063 alloy according to the International AA alloy standard but where the concentration of Cu is between 0.005 and 0.05 wt% and the concentration of Zn is between 0.025 and 0.10 wt%.

According to a third exemplary aspect, the alloy according to the first or second aspect may be characterized in that the minimum concentration of Cu is 0.010 wt%.

According to a fourth aspect, the alloy according to any of the first to third aspect may be characterized in that the maximum concentration of Cu is 0.04 wt%.

According to a fifth exemplary aspect, the alloy according to any of the first to third aspect may be characterized in that the maximum concentration of Cu is 0.03 wt%.

According to a sixth aspect, the alloy according to any of the first to third aspect may be characterized in that the maximum concentration of Cu is 0.025 wt%.

According to a seventh exemplary aspect, the alloy according to any of the first to sixth aspect may be characterized in that the minimum concentration of Zn is 0.030 wt%. According to an eight exemplary aspect, the alloy according to any of the first to seventh aspect may be characterized in that the maximum concentration of Zn is 0.08 wt%.

According to a ninth exemplary aspect, the alloy according to any of the first to seventh aspect may be characterized in that the maximum concentration of Zn is 0.06 wt%.

According to a tenth exemplary aspect, the alloy according to any of the first to seventh aspect may be characterized in that the maximum concentration of Zn is 0.055 wt%. According to an eleventh exemplary aspect, the alloy according to any of the first to seventh aspect may be characterized in that the maximum concentration of Zn is 0.05 wt%. According to a twelfth exemplary aspect, the alloy according to any of the first to seventh aspect may be characterized in that the maximum

concentration of Zn is 0.050 wt%.

According to a thirteenth exemplary aspect, the alloy according to any of the first to twelfth aspect may be characterized in that the ratio of Cu/Zn is between 0.8 and 0.2.

According to a fourteenth exemplary aspect, the alloy according to any of the first to twelfth aspect may be characterized in that the ratio of Cu/Zn is between 0.5 and 0.2.

According to a fifteenth exemplary aspect, the alloy according to any of the first to fourteenth aspect may be characterized in that the concentration of Fe is between 0.22 and 0.37 wt%.

According to a sixteenth exemplary aspect, the alloy according to any of the first to fifteenth aspect may be characterized in that the concentration of Mn is between 0.03 and 0.06 wt%.

According to a seventeenth exemplary aspect, the alloy according to any of the first to sixteenth aspect may be characterized in that the concentration of Mg is between 0.30 and 0.50 wt% and the concentration of Si is between 0.35 and 0.50 wt%.

Example 1.

The tests were initially carried out with alloys having a chemistry as defined in table 1 below. The concentrations of Si, Mg and Mn in these tested alloys are kept close to constant, while the concentrations of Fe and Zn are varied. To alloys 1 1 , 12 and 17 it was added 0.05 wt% Cu.

Tablel . Chemistry of tested alloys and extrusions.

One log/billet of each alloy was, after casting, homogenized together (at the same time) with the following specified time-temperature path:

- Heating rate 200-300 °C/h to 575 °C.

- Holding at 575 °C for 2 hour and 15 minutes.

- Then cooling at a cooling rate of 350 °C/h.

After homogenisation the billets were extruded in an 800 tons vertical press with a container diameter of 100 mm and a billet length of 200 mm. Prior to extrusion the billets were preheated by induction heating at approximately 100 °C/min to an average temperature 520 °C. The container temperature was approximately 430 °C and the extrusion ratio was 78.5. The ram speed was 4.4 mm/s, while the profile speed was 22 m/min. After extrusion, the profiles were air cooled to room temperature and then stretched to approximately 0.5% plastic strain.

The extruded profiles were further aged (dual rate) as follows:

- Heating from room temperature to 150: ~ 40 min.

- Holding at 150 °C for approximately 30 min.

- Heating from 150 °C to 195 °C at a rate of 15 °C/h .

- Time at final temperature 195 °C, 2 hours.

The 18 newly extruded profiles were mounted horizontally and etched in an industrial 15000 litres NaOH etching bath with AI8000 additive (commercially available product). The temperature was 70 °C and the etching time was 15 minutes.

Finally, the etched profile samples were anodized, also in normal production.

Evaluation of anodized surfaces.

Figures 2 - 8 show as stated above SEM micrographs of the tested profile surfaces together with concentrations of Fe, Zn and Cu together with images of anodises samples.

From Figs. 2, 3 and 4 it appears that increasing Fe reduce the gloss values when the Zn content is more than 0.03 wt%. As is further apparent from Fig. 2, PGE is slightly reduced with increasing Fe from 0.22 to 0.37 wt%. At 0.04 wt% Zn and higher, Figs. 3 and 4, the effect of increasing Fe on PGE is negligible.

Fig. 6 shows that there is not observed any effect on gloss and PGE when increasing Mn from 0.06 to 0.12 wt%. Further, Fig. 5 shows that gloss is strongly increased when increasing Zn from 0.03 to 0.05 wt%, but gloss is slightly reduced when increasing Zn even higher, i.e. from 0.05 to 0.07 wt%.

The effect of Cu on PGE and gloss is, however, remarkable when being added to the alloy containg 0.05 wt% Zn and 0.30 wt% Fe, as can be seen in Fig. 8. This effect is on the other hand not evident with higher Zn level, 0.07 wt % as is apparent from Fig. 7. Figure 17 (Trial 1 1 ) shows an overview of the results obtained in Example 1 .

Gloss was measured at an angle of 60° along the extrusion direction using a handheld measurement device.

The positive test results from the experiments that were done under Example 1 relating to the effect of Cu on alloys containg Zn led to the conclusion that further test should be done with alloys containing different ranges of Cu in relation to Zn. Such test were carried out under the following example.

Example 2.

Additional test were carried out on alloys with varying ranges of Cu and Zn concentrations as defined in the table below:

Table 2. Chemistry of tested alloys and extrusions with varying ranges of Cu and Zn concentrations.

As can be seen from Table 2, the concentrations of Si, Mg, Fe and Mn are basically kept the same for all of the alloys, while the concentrations of Cu and Zn are varied. The alloys as defined in table 2 were cast, heat treated, extruded to profiles, stretched, aged, etched and anodized the same way and under the same conditions as under example 1 above.

The initial three alloys in Table 2, B1 , B2 and B3, correspond respectively to alloys A4, A10 and A1 1 in Table 1 above from example 1 and are included in the alloy matrix as reference material.

Fig. 9 shows micrographs of profiles of these former tested alloys B1 , B2 and B3 together with diagrams showing the Cu and Zn concentrations and as can be clearly seen from this figure, the PGE is vastly reduced or absent with the addition of 0.05 wt% Cu.

Figs. 9, 10, 1 1 and 12 shows SEM micrographs together with diagrams showing the Cu and Zn concentrations for each respective depiction. The results as shown in these figures confirm the observations under the initial tests as commented in Example 1 above that addition of Cu reduces gloss and PGE on Zn containing 6060 and 6063 types alloys. Further, Figs. 18 to 22 show an overview of the surface qualities obtained in Example 2.

Based on the tests under the examples above it has been possible to optimize the addition of Cu in relation to Zn to obtain the desired reduced gloss and PGE as defined in the claims. On the other hand, the content of Cu should be as low as possible to reduce the possibility of corrosion, even below 0.010 wt%. Further, the content of Zn should not be too high, since for example it may result in accumulation of Zn in the etching bath, which in turn results in higher risk for PGE.

Fig. 13 shows as formerly stated a summary of 6xxx alloys with different

concentrations of Cu and Zn in relation to visual observation of developed PGE on the surface during the anodizing process. The circular spots are observed, tested surfaces where the degree of PGE is low and well within acceptable level, while the crosses are observations where the PGE level is too high and not acceptable. Based on the observations as depicted in Fig. 13, the frame drawn up by dotted lines shows the scope of protection, i.e. the area within the Cu, Zn diagram showing which levels or which combinations of Zn and Cu where PGE is not developed for the subject 6xxx alloys that have been tested. Thus, it is clearly shown in Fig. 13 that PGE is within an acceptable level if Cu is below 0.05 wt% and Zn below 0.10 wt% and the ratio of Cu/Zn is below 1 .

Example 3

Further experiments have been carried out on alloys with varying ranges of Cu and Zn concentrations as defined in the table shown in Fig. 14a. The experiments have been conducted in different locations A, B, C, D, E, F, G, H and I as is apparent from the table. In this respect, each location represents a geographically separate facility. As is further apparent from Fig. 14a, the tests were carried out using different billet diameters and profile cross sections that were prepared similar to the procedure described for Experiment 1 . Further, Fig. 14b shows the chemical compositions of the samples mentioned in the table of Fig. 14a. The samples mentioned in Fig. 14a are identifiable in Fig. 14b by their cast name and by their Cu and Zn compositions. As is apparent, the samples were either air cooled or water quenched ("Water Q") after extrusion.

The samples were then analyzed as described above and the results are shown in Figs. 15, 16, 23, 24 and 25 as well as in the table shown in Fig. 14a. Fig. 26 shows a combined view of the obtained results of all experiments 1 , 2 and 3. Fig. 13 shows a subset of the data shown in Fig. 26. In this respect, in Figs. 15 to 27, "OK" indicates a good surface quality with no PGE and good optical properties. Further, ΌΚ- " indicates an acceptable surface quality potentially with light PGE and optical properties that are acceptable for several applications, and "PGE" indicates that more severe PGE occurred that resulted in a surface quality that is considered to be insufficient but might still be acceptable depending on the use environment in some cases.

As can be seen, there are slight variations for the same samples depending on the location in which the trial was conducted. There are further slight variations for the same sample and the same location when a trial was repeated. It is assumed that these differences are caused by slight process variations that cannot be accounted for by current process control, such as variations of conditions in the etching bath. Environmental conditions such as humidity and temperature may also influence the results.

Accordingly, embodiments of the present invention define composition ranges that allow an efficient production of efficient alloys for etching and/or anodizing and give consistent results even when the process parameters, that cannot be efficiently controlled by production means, fluctuate.

Further tests have been carried out with alloys in different temper conditions as shown in Fig. 27. It has been found that if the material is in T1 or T4 temper condition, a relation between Zn and PGE is no longer apparent, and the alloys also generally exhibit higher susceptibility for PGE (right view in Fig. 27). Accordingly, the alloys and products according to the invention may be characterized by having a temper condition other than T1 or T4, e.g. by having a temper condition selected from: T2, T3, T5, T6, T7, T8, T9 or T10.