CN113316662A

CN113316662A - Continuous surface treatment of coils made of aluminium alloy sheet

Info

Publication number: CN113316662A
Application number: CN202080009290.XA
Authority: CN
Inventors: M·勃姆; 李吉超
Original assignee: Baoling Greenken Aluminum Co ltd; New Brisasken United Aluminum
Current assignee: Baoling Greenken Aluminum Co ltd; New Brisasken United Aluminum
Priority date: 2019-01-18
Filing date: 2020-01-17
Publication date: 2021-08-27
Also published as: FR3091880A1; KR102824900B1; CA3125813A1; JP2022517659A; JP7621258B2; KR20210113249A; EP3911780B1; FR3091880B1; US20220090269A1; EP3911780A1

Abstract

本发明涉及适用于5XXX铝合金板和6XXX铝合金板的卷材的连续卷材表面处理方法。所述方法包括以下连续步骤：用无氟酸性溶液蚀刻表面；用去离子水冲洗；施用包含钛和锆的转化溶液，以及干燥。本发明表面处理方法是环境友好的，并且能够以有效的且可靠的方式制备5XXX和6XXX合金处理表面。其特别适合用于制备用于汽车工业的铝合金板。The invention relates to a continuous coil surface treatment method suitable for the coils of 5XXX aluminum alloy plates and 6XXX aluminum alloy plates. The method includes the following sequential steps: etching the surface with a fluorine-free acidic solution; rinsing with deionized water; applying a conversion solution comprising titanium and zirconium, and drying. The surface treatment method of the present invention is environmentally friendly and enables the preparation of 5XXX and 6XXX alloy treated surfaces in an efficient and reliable manner. It is particularly suitable for producing aluminium alloy sheets for the automotive industry.

Description

Continuous surface treatment of coils made of aluminium alloy sheet

Technical Field

The present invention relates to the field of continuous surface treatment of sheets and strips made of aluminium alloys and of parts stamped from these sheets, in particular alloys of the 5xxx or 6xxx type intended for the manufacture of automotive body parts, according to the provisions of the aluminium Association

Background

Aluminum is increasingly used in automotive construction to reduce the weight of the vehicle, thereby reducing fuel consumption and emissions of pollutants and greenhouse gases. The sheet material is used in particular for the production of body skin parts, such as engine hoods and doors, and structural parts. This type of application requires a set of properties of mechanical strength, corrosion resistance and formability that are sometimes contradictory; mass production is carried out at an acceptable cost.

For automotive parts, surface preparation suitable for assembly operations, in particular adhesive bonding and welding, may be required. These pretreatments are time-consuming and expensive, in particular because the bath is corrosive and requires special precautions for health and the environment. For environmental reasons, recent treatments are free of chromium and use elements such as organic phosphorus, silanes and derivatives, titanium and/or zirconium. Such treatments are described, for example, in patents and applications US 5,514,211, US 5,879,437, US 6,167,609, US2013/284049, US2011/041957, US 2016/319440.

Patent FR2856079 describes a simplified alternative treatment by using atmospheric plasma.

Patent US 5,868,872 discloses a chromium-free, wash-free process, particularly for applications in the food packaging industry. This patent does not disclose an etching step prior to treatment, but only discloses acidic or alkaline cleaners.

Patent US 6,562,148 discloses a method for the pretreatment of workpieces having a surface made of aluminum or aluminum alloys, comprising rinsing with an acidic aqueous solution containing an inorganic acid, rinsing with water, contacting with an acidic aqueous solution free of chromium and free of polymers and containing Ti and Zr as fluoride ion complexes in a Ti: Zr weight ratio of 2:1 to 1: 2.

Patent application EP 2537674 a1 discloses an aluminum or aluminum alloy material having a surface-treated coating film capable of maintaining hydrophilicity, high corrosion resistance, antibacterial properties, and deodorizing properties for a long time on the surface of a base material formed of aluminum or an aluminum alloy.

Surface preparation is typically performed using a continuous web surfacing line capable of surfacing the web of sheet.

The surface treatment line may include continuous solution heat treatment and quenching, or may be a line dedicated to surface treatment. By optimizing the weight of the chemical layer, a plurality of surface treatment steps are applied to progressively change the surface characteristics to meet the application of the product in the automotive field. The first surface treatment step is generally a degreasing step of the plates, intended to remove the oily residues present on the plates, which are present after the last rolling step. After the rolling process, the surface of the aluminum material comprises a "disturbed region", also called "disturbed layer" or "disturbed surface layer", and the oxide layer and the disturbed region are removed by etching in a second surface treatment step to ensure a uniform surface, which is more favorable for deposition of products such as Ti/Zr transition layers and for further corrosion/adhesion durability properties. The third surface treatment step is a conversion coating, the purpose of which is to deposit precisely a layer weight (for example consisting of Ti and/or Zr) which promotes adhesion and corrosion resistance. It is generally believed that the use of fluorine is necessary in the second etch process in order to eliminate "perturbation zones" and obtain a surface that is favorable for the deposition of the conversion layer. However, the use of fluorine-containing baths requires special precautions for health and the environment. Another requirement is that surface treatment lines dedicated to automotive applications must be able to treat coils of 5XXX and 6XXX alloy sheets instead. Therefore, it is economically advantageous to maintain the same treatment regime for different types of alloys.

It is an object of the present invention to develop a more environmentally friendly improved surface treatment process to produce a treated surface in an efficient and reliable manner to provide a treated surface for 5XXX and 6XXX alloys.

Disclosure of Invention

One object of the present invention is a continuous coil surface treatment process suitable for coils of 5XXX and 6XXX aluminium alloy sheet having a surface, comprising the following successive steps:

a) optionally cleaning the surface of the aluminum alloy sheet;

b) etching the surface of the aluminum alloy plate which is optionally cleaned by using a fluorine-free acid solution;

c) washing the etched surface of the aluminum alloy plate by using deionized water;

d) applying a conversion solution comprising titanium and zirconium to the surface of the etched aluminum alloy sheet, wherein the weight ratio of zirconium to titanium is from about 3.0 to about 5.0, preferably from 3.2 to 4.0;

e) optionally washing the surface of the aluminum alloy plate after conversion with deionized water; and

f) and drying the surface of the aluminum alloy plate.

Drawings

Fig. 1a is an SEM micrograph of a6016 surface etched with a fluorine-containing etching solution, and fig. 1b is an SEM micrograph of a6016 surface etched with a fluorine-free etching solution.

Detailed Description

Unless otherwise indicated, all aluminum alloys mentioned below are named using the rules and names defined by the aluminum association in the regularly issued Registration Record Series.

The definition of the standard EN 12258 applies, unless otherwise stated.

The process of the present invention is a continuous coil surface treatment process suitable for coils of both 5XXX and 6XXX alloy sheets. One significant advantage of the present invention is that no changes or modifications to the process are required when switching the wire from a 5XXX alloy to a 6XXX alloy.

The process is suitable for the treatment of coils made from 5XXX alloy sheets as well as coils made from 6XXX alloy sheets. Preferably the coil is a coil of sheet made of an aluminium alloy selected from the group consisting of: AA5754, AA5182, AA6451, AA6605, AA6005A, AA6016, AA6116, AA6022, AA6013, AA6056, AA6156, AA6111 and AA 6014.

In a first step, the surface of the sheet may optionally be cleaned. Cleaning may be used to remove residual oil left in the rolling process. Optionally, cleaning can be performed by hot water spraying and/or by using organic solvents and/or by using surfactants and/or detergents, e.g. alkaline detergents. For some continuous processing lines, the sheet material may have been sufficiently degreased by previous heat treatments and may not require a cleaning step. Further, in some cases, cleaning and etching may be performed simultaneously to simplify the process. For productivity and cost reasons, it is generally preferred to avoid the cleaning step.

In a next step, the surface of the optionally cleaned aluminium alloy sheet is etched with a fluorine-free acidic solution. The inventors of the present invention have found that by combining a fluorine-free acidic solution with a conversion bath containing specific amounts of Ti and Zr, it is possible to treat 5XXX and 6XXX sheets with the same bath and obtain satisfactory conversion. Preferably, the etching using the fluorine-free acidic solution is performed chemically, not electrochemically.

Preferably, the fluorine-free acidic solution comprises sulfuric acid, nitric acid, phosphoric acid, or a mixture thereof. Advantageously, the fluorine-free acidic solution comprises at least 80% sulfuric acid and phosphoric acid, or a mixture thereof. In one embodiment, the fluorine-free acidic solution does not comprise nitric acid. If mixtures of acids are used, it is advantageous to use mixtures of acids comprising at least 80% sulfuric acid. Advantageously, the concentration of sulfuric acid in the fluorine-free acidic solution is from about 2g/l to about 60g/l, preferably from 15g/l to 50 g/l. Optionally, the fluorine-free acidic solution may include one or more additives (e.g., surfactants and/or detergents) and/or one or more accelerators. The fluorine-free acidic solution may include a surfactant and/or detergent additive at a concentration ranging from about 0.05 wt% to 3 wt%. Preferably, the fluorine-free acidic solution may include a surfactant and/or detergent additive at a concentration ranging from about 0.1 wt% to 2.5 wt%, from about 0.2 wt% to 2 wt%, from about 0.3 wt% to 1.5 wt%, or from about 0.4 wt% to 1.3 wt%. Suitable promoters that may be included in the fluorine-free acidic solution include iron sulfate. The promoter may be included in the fluorine-free acidic solution at a concentration ranging from about 0.005 wt% to 0.4 wt%. For example, the accelerator may be included in the fluorine-free acidic solution at a concentration ranging from about 0.01 wt% to 0.3 wt%, about 0.03 wt% to 0.2 wt%.

The fluorine-free acidic solution may be heated to a temperature of about 55 ℃ to about 85 ℃. The fluorine-free acidic solution can be controlled within the temperature and concentration ranges outlined using, for example, heat exchangers and metering pumps, as well as flooding and appropriate replacement or replenishment.

The fluorine-free acidic solution may be applied by spraying the solution onto the sheet or by dipping the sheet into a bath of molten metal. Preferably, the fluorine-free acidic solution is applied by immersion. Optionally, the fluorine-free acidic solution may be circulated to ensure continuous exposure of fresh solution to the sheet surface. In an advantageous embodiment, the fluorine-free acidic solution is continuously treated with an exchange resin to maintain defined amounts of Al and Mg ions in the solution. Preferably, the fluorine-free acidic solution includes less than about 3g/l of aluminum ions and magnesium ions. Advantageously, the fluorine-free acidic solution may comprise less than 2g/l of aluminium and magnesium ions. The contact time for the acid etching step may be from about 5 seconds to about 30 seconds or preferably from about 10 to about 20 seconds.

Advantageously, the etching removal is from 0.01 to 0.2g/m for 6XXX alloys²Preferably 0.01 to 0.1g/m²And 0.1 to 0.2g/m for 5XXX alloys². Using the fluorine-free acidic solution of the present invention, the etch removal is substantially lower than that of the fluorine-containing acid solutions known in the prior art. This is advantageous in limiting Al and Mg ions in the solution. Furthermore, the inventive etching provides a smoother surface, in particular with less or even no pitting, than the prior art etching is advantageous.

And washing the surface of the etched aluminum alloy plate by using deionized water after etching. Preferably, the conductivity of the deionized water in this step is less than or equal to 50. mu.S/cm. The rinsing step is preferably carried out at a temperature of from about 37 ℃ to about 70 ℃. Advantageously, the rinsing step may be carried out at a temperature of from about 40 ℃ to about 65 ℃ and preferably from about 45 ℃ to about 60 ℃. The flushing may be a progressive cascade system. Preferably, a nebulizer is used in the rinsing step.

The next step is to apply a conversion solution comprising titanium and zirconium to the surface of the etched aluminum alloy sheet, wherein the weight ratio of zirconium to titanium is from about 3.0 to about 5.0, preferably from 3.2 to 4.0. The inventors of the present invention have found that by combining etching with a fluorine-free acidic solution and conversion with a conversion solution according to the present invention, Zr/Ti weight ratios of about 0.8 to about 1.3 can be obtained on the treated sheet surface for 5XXX and 6XXX alloys. This ratio is important for the adhesion properties of the sheet material. One benefit of the present invention is that there is no need to alter the composition of the conversion solution in order to handle both 5XXX and 6XXX alloys. The conversion solution may be applied at a temperature of about 35 ℃ to about 65 ℃. Preferably, the conversion solution is applied at different temperatures for 5XXX and 6XXX, typically at a temperature of from about 40 ℃ to about 50 ℃ for 5XXX alloys and from about 45 ℃ to about 55 ℃ for 6XXX alloys. The contact time for applying the conversion solution can be from about 5 seconds to about 20 seconds. Preferably, the contact time for applying the conversion solution is different for 5XXX and 6XXX, preferably from about 5 seconds to about 9 seconds for 5XXX alloys, typically from about 7 seconds for 5XXX alloys, and from about 8 seconds to about 12 seconds for 6XXX alloys, typically about 10 seconds for 6XXX alloys.

Preferably, the conversion solution comprises titanium and zirconium, wherein the titanium content is from about 20 to about 200mg/l, preferably from 60 to 140 mg/l. Advantageously, the conversion solution comprises hexafluorotitanic acid, hexafluorozirconic acid, hydrofluoric acid and optionally ammonium bifluoride. Additional fluoride (in the form of hydrofluoric acid and optionally ammonium bifluoride) is advantageously added to complex the Al generated during treatment with the conversion solution. The pH of the conversion solution is advantageously adjusted upwardly to a pH of from about 2.5 to about 4.5, preferably from 3.5 to 4, by the addition of a base, such as ammonium hydroxide or ammonium bifluoride. In an advantageous embodiment, the conversion solution is continuously treated with an exchange resin to maintain defined amounts of Al and Mg ions in the solution. Preferably, the conversion solution contains less than about 80ppm of aluminum ions and magnesium ions.

The conversion solution may be applied by spraying the solution onto the sheet or by dipping the sheet into a bath of molten metal. Preferably, the conversion solution is applied by spraying the aluminium alloy sheet with the conversion solution, preferably using at least 5 spraying ramps. The application of the conversion solution according to the invention by roll coating is not good, since the Ti/Zr ratio on the sheet will be the same as in the conversion solution.

The next step is to optionally rinse the surface of the converted aluminum alloy sheet with deionized water.

The final step is drying the surface of the aluminum alloy sheet. The drying step removes all water from the surface of the panel. The drying step may be performed using an air dryer or an infrared dryer. The drying step may be performed for a period of up to five minutes. The drying step can also be used for metallurgical purposes, if desired, in particular for 6xxx alloys, so that the coil temperature is advantageously from 50 ℃ to 120 ℃ or preferably from 60 ℃ to 100 ℃.

Examples

The surface of the aluminium alloy sheet is treated on a continuous line according to the process described herein. The plate material includes 5182 aluminum alloy plate and 6016 aluminum alloy plate. The panels were cleaned and, for tests 1 and 2, by melting the bath (H) with thiofluoro-hydrogen₂SO₄Etching was carried out by spraying with 0.4g/l HF, 8g/l, 50 ℃ C., or by using a sulfuric acid bath (H) for tests 3-6₂SO₄43g/l 70 ℃ C.) was sprayed for etching. SEM micrographs of the 6016 alloy surface etched with a bath of hydrogen-thio-fluoride (run 2) and 6016 alloy surface etched with a bath of sulfuric acid (run 6) are shown in fig. 1a and 1b, respectively. The inventive etch provides a smoother surface with much less pitting than the prior art etches would be advantageous. After etching, the plates were rinsed with deionized water and treated by spraying with a Ti/Zr conversion surface treatment comprising hexafluorotitanic acid, hexafluorozirconic acid, hydrofluoric acid and ammonium bifluoride at a pH of 3.8. The contact time, concentration and temperature are shown in table 1.

The amounts of Zr and Ti deposited on the surface were measured by XRF at three positions in the width direction, and six samples were measured. The average values of the measurements are provided in table 1.

TABLE 1

The conversion coating using the molten bath C is according to the invention. Using the process of the invention, Zr/Ti ratios between 0.8 and 1.3 can be obtained with a single bath for 5XXX and 6XXX alloys, and an advantageously smoother surface is obtained.

Claims

1. A continuous coil surface treatment process suitable for use with a coil of 5XXX and 6XXX aluminum alloy sheet having a surface, comprising the following successive steps:

a) optionally cleaning the surface of the aluminum alloy sheet;

f) and drying the surface of the aluminum alloy plate.

2. The process of claim 1, wherein the conversion solution comprises titanium and zirconium, wherein the titanium content is from about 20 to about 200mg/l and preferably from 60 to 140 mg/l.

3. A process according to claim 1 or claim 2, wherein the conversion solution comprises hexafluorotitanic acid, hexafluorozirconic acid, hydrofluoric acid and optionally ammonium bifluoride.

4. The method of any one of claims 1-3, wherein the fluorine-free acidic solution comprises sulfuric acid, nitric acid, phosphoric acid, or a mixture thereof.

5. The process according to any one of claims 1 to 4, wherein the concentration of sulfuric acid of the fluorine-free acidic solution is from about 2g/l to about 60g/l, preferably from 15g/l to 50 g/l.

6. The method of any of claims 1-5, wherein the aluminum alloy sheet is made from an aluminum alloy selected from the group consisting of: AA5754, AA5182, AA6451, AA6005, AA6605, AA6005A, AA6016, AA6116, AA6022, AA6013, AA6056, AA6156, AA6111 and AA 6014.

7. The method according to any one of claims 1-6, wherein the applying in step (d) is performed by dipping the aluminum alloy sheet into a conversion solution.

8. The method according to any one of claims 1-6, wherein the applying in step (d) is performed by spraying the aluminum alloy sheet with a conversion solution.

9. The method according to any one of claims 1 to 8, wherein the etching in step (b) is performed by spraying the aluminum alloy sheet with a fluorine-free acidic solution.

10. The method of any one of claims 1-9, wherein the fluorine-free acidic solution in step (b) comprises less than about 2g/l of aluminum ions and magnesium ions.

11. The method of any one of claims 1-10, wherein the fluorine-free acidic solution includes a surfactant additive or accelerator and is used at a temperature of about 55 ℃ to about 85 ℃ for about 5 to about 30 seconds.