DE4438608C2 - Process for coating an aluminum substrate - Google Patents

Description

The invention relates to a method for coating an aluminum sheet with zinc and manganese through physical vapor deposition (PVD). An aluminum or steel substrate with one cracked accordingly The layer of a zinc-manganese alloy is from the patents abstracts of Japan C-601 May 29, 1989, Vol. 13 / No. 233 under No. 1-42572 (A) be knows. Furthermore, the expert knows from GB-PS 1187 802 a PVD-Ver drive to apply Zn-Mn layers to steel sheets, the one individual components from separate sources evaporated and the substrate one after the other through chambers with the corresponding steam sources is carried out.

To show how particularly advantageous coated substrates cheap in industrial way, d. H. can be produced in series production Object of the present invention.

To solve this problem, the characteristic features of the An Proposition 1 provided. Advantageous further training is the content of the Unteran claims.  

Aluminum sheets with the layer mentioned systems are particularly good for the construction of vehicles bodies suitable. The requirements regarding Weldability, corrosion protection and paint adhesion properties shaft are optimally fulfilled. It is by the Coating technology using vapor phase deposition as well due to the additional manganese content, especially the Zinc consumption compared to the usual, galvanic or melt-dipping coating techniques reduced. Furthermore, on sheets with Zn-Mn mix layers or corresponding multi-layer systems gere infiltration of the paint layer in case of injury, e.g. B. in the event of stone chips, scratches, etc. compared to pure zinc coated sheets observed. Also, the manganese is considered Cover layer or as part of a mixed layer manufacturing reasons advantageous because it elek is tric conductive and thus spot welding the accordingly coated substrate allowed, and also in a subsequent phosphating and a Subsequent dip painting does not interfere, especially especially since manganese is a minor component of the dip coating is. In particular, however, coating processes are un ter with the help of physical vapor phase separation dung, d. H. PVD technology (physical vapor deposi tion) in contrast to the usual galvanic Coating process or your usual Feuerver prong environmentally friendly processes. This in Beschich processing chambers performed in a high vacuum PVD process are largely waste-free and low-emission.

In a particularly simple manner, the zinc content in the applied layer of thermal evaporators, the also called sources are provided. Of the Manganese portion of the coating is made using conventional cher, usual in PVD coating technology, such as  Sputtering, by electron beam ver vapor or by arc evaporation, the can be carried out anodically or cathodically brings.

The presence of a plasma near the layer Education on the substrate has become particularly important for the Electron beam evaporation and thermal ver vaping proved to be advantageous. This plasma works supportive in the formation of an optimal layered layer tung. The additional plasma can be separated by a sepa rat attached ion source inside or outside arranged in a conventional coating chamber net can be generated.

Also with regard to an improved layer adhesion can in particular before applying a mixed layer a so-called adhesion promoter layer is vapor-deposited from Zn and Mn be the case with aluminum substrates made of aluminum consists.

The formation and the production of a Zn + Mn multilayer system is with reference to the Prin zipskizze of FIG. 1 and that of a Zn-Mn-mixed layer with reference to the schematic diagram of FIG. 2 explained.

As shown in FIG. 1, a zinc layer (Zn) and a manganese layer (Mn) are first applied to a substrate by vapor phase deposition. This can be done in two known, arranged one behind the other coating chambers. The so-called sources, which are loaded with zinc or with manganese, are arranged in these chambers. The zinc from thermal sources and the manganese are preferably produced from anodic or cathodic arc discharge sources.

Of course, a white on the manganese layer tere zinc layer and on top of this another manganese layer be applied. To do this, the substrate must be further Coating chambers are introduced. Is also through the type and positioning of the metal steam sources in the coating chambers the type of to be generated Layer or layers as well as the supported layer thickness influenceable. Another parameter, with the help of it The formation of the layer can be varied Dwell time of the substrate in the respective Coating chamber.

If - as shown in FIG. 2 - a mixed layer ZnMn consisting of the components zinc and manganese are to be produced, the corresponding sources must be arranged in a single coating chamber and simultaneously evaporated. In order to obtain the desired individual proportions of zinc and manganese, ie the so-called mixture gradients, sources with different amounts of evaporation can be used. The desired setting of the gradient is also possible by varying the number and the positioning of the zinc or manganese sources. A suitable adhesion promoter layer HVS can be applied in front of the mixed layer.

How this coating method can be carried out particularly advantageously in an industrial manner, ie in series production, is explained below with reference to the schematic diagram according to FIG. 3, in which a system concept for carrying out the method described in subclaims 4 to 10 is outlined. Essential to the invention can be all specified features; in particular, however, it is provided that the metal sheet to be coated is lined up, partially sealed off from the processing zones, in which different pressure ratios correspond to the respective processing step, and between which pressure locks are provided. In this respect, this method works similarly to a coating system known from US Pat. No. 4,763,601, but in which chemical vapor phase deposition takes place. Furthermore, a working with physical vapor deposition coating system with partially similar features is known from US 5,236,509.

In detail, a still uncoated sheet 1 is delivered as a coil 2 and is continuously unwound at the beginning of the individual processing stations in area 3 . First, each developed section of the sheet 1 passes through a cleaning zone 4 , after which further transport according to the direction of the arrow 5 takes place through a pressure lock 6 a into a dry etching station 7 . From this water, the sheet 1 passes through a further pressure lock 6 b into a coating zone 8 , which is followed by a further pressure lock 6 c. Sluice from the pressure 6 c exiting passes the sheet 1 in a post treatment zone 9 and via a further pressure lock 6, finally, d in the area 10 where the sheet is rewound onto a coil 2. 1

Specifically, the sheet 1 me can be mechanically freed of dust, scale, etc. in the cleaning zone and is then cleaned wet-chemically with or without ultrasound support. In an aqueous solution, fats and oils are chemically removed or washed off the surface. In a warm-up stage which may be integrated in the cleaning zone 4 , the sheet metal 1 can then be heated to approximately 120 ° C. by inductive heating; the residual water from the cleaning zone 4 is evaporated from the sheet surface and the sheet 1 is preconditioned for the subsequent coating process. However, the sheet 1 can also come directly from an annealing furnace, the method according to the invention being carried out in a rolling mill. Then there is no coil 2 at the beginning, rather the sheet 1 is then quenched before wet-chemical cleaning, for example to 150 ° C. All of the treatment steps explained in connection with the cleaning zone 4 do not require any special atmosphere, ie they can be carried out under ambient pressure.

In contrast, in the dry etching station 7, the surfaces (top and bottom) of the sheet 1 are cleaned by means of plasma etching under vacuum and an inert gas atmosphere. This is a dry physical process that is carried out at pressures between 1 mbar and 1 µbar. If the sheet is an aluminum sheet, the surface of adhesion-inhibiting compounds, such as. B. alumina, - hydroxide and unwanted accompanying elements such as Na, Ca, K, etc. exempt. For this purpose, gases and / or gas mixtures are introduced into the dry etching station 7 designed as a chamber. The upper layers of the sheet surface are then removed using a plasma discharge between sheet 1 and the wall of the chamber. The plasma is generated by DC or high-frequency superimposed high voltage or by a microwave-induced discharge. The working gas can consist of argon, hydrogen, oxygen, typically a hydrogen-oxygen mixture is used at the beginning and argon at the end of the etching process. As already mentioned, oxide, hydroxide and hydride layers are generally removed, ie also in the case of steel sheets.

In the coating zone 8 , the sheet 1 with its generated in the dry etching station 7 , practically metallic clean surface on the metal vapor or metal atoms he generating sources, such as target, boat, evaporator block, crucible, etc. is passed. As a result, metals are deposited or deposited on the sheet surface. In order to ensure reproducible optimum adhesion, the sheet 1 can be charged negatively with respect to the chamber wall of the coating zone 8, which is also formed as a chamber. Typical values for this bias voltage are -100 to -400 V.

The following layers are preferably applied at ^negative pressures in the range from 10 ^-3 mbar to 10 ^-6 mbar:

• - Zn layer in the thickness of 0.5 to 10 microns and a Mn layer in the thickness of 0.1 to 3 µm in Kombina tion, d. H. it becomes a multi-layer and / or mixed layer system manufactured.
• A preferred layer combination is a Zn Layer in the thickness of 2 to 7 microns and a Mn Layer in the thickness of 0.5 to 2 microns.
• - A preferred mixed layer system consists of ZnMn with Zn / Mn = 70/30 to 50/50 atomic percent.
• - A typical single-layer system or monolayer stands from Zn in the thickness of 0.1 to 1 µm and / or Mn in the thickness of 0.1 to 0.5 µm.

The layer system Zn + Mn is thermal Evaporate the zinc layer and then apply it the Mn layer preferably by anodic arc discharge or electron beam evaporation. The system ZnMn is - as already explained - preferably by means of Combination of standing coating sources shown, d. H. the evaporator sources become serial and / or arranged in parallel and thereby create a mix layer. Suitable sources are thermal, electrons blasting and anodic arc discharge sources.  

Overall, the use of physical vapor phase deposition, ie PVD technology (physical vapor deposition), makes it possible to coat almost any material with any material and its combinations. PVD techniques, especially vapor deposition in a high vacuum and cathode sputtering, are particularly suitable for the coil coating. Under the term "vapor deposition in a high vacuum" should include the process of thermal vapor deposition, vapor deposition using an electron beam and anodic arc discharge. The term "cathode sputtering" includes processes such as sputtering and cathodic arc discharge. An additional plasma discharge should be formed, in particular in the method "vapor deposition in a high vacuum", in which no plasma stains the metal vapor ion. The type of metal steam generation, ie the type and the positioning of the metal steam sources, is determined by the type of layer or layers to be produced and the required layer thickness. Furthermore, the throughput speed of the sheet 1 unwound from the coil 2 passes through the coating zone 8 , ie the speed must also be taken into account when selecting the metal vapor sources.

In the aftertreatment zone 9 , the layer applied in the coating zone 8 can be thermally stabilized. This is particularly necessary if the layer (s) consists of more than one component. This is realized by induction heating of the sheet 1 to an adjustable temperature which is dependent on the material of the sheet. A typical temperature value is in the range from 130 ° C to 180 ° C. In this post-treatment zone, which is of course again or can be designed as a chamber, there is still negative pressure.

Furthermore, the sheet 1 can be continuously cooled to about 60 ° C. in this treatment zone. Ar gon and / or nitrogen can be blown into the chamber, as a result of which the reactive particles become saturated in the sense of a residual reaction.

Furthermore, a further protective layer can be applied to the sheet 1 in the aftertreatment zone 9 , but then preferably under ambient pressure, ie following the pressure lock 6 d, which may also be omitted. It is possible to apply a layer of lacquer by spraying, this special lacquer layer should be thermoformable and suitable for use in adhesive bonds. A further possibility is the application of an electrically conductive layer consisting of polymers, which is formed by means of plasma polymerization, in order to enable subsequent cathodic acid treatment, ie electrolytic cathodic coating.

The individual pressure locks 6 a, 6 b, 6 c and possibly 6 d un support the maintenance of the desired pressure level in the respective adjacent processing zones formed as chambers that are isolated from the environment. In or at the pressure locks 6 a to 6 d, corresponding pump stages or pumps can then be connected, which produce the desired pressure level.

In general, the process sequence described is particularly suitable for sheet metal coating using a PVD process. The system described can of course not only be loaded with a quasi-endless sheet metal strip that is unwound from the coil 2 , but short sheet metal sections can also be sent through the system outlined. All of the layers mentioned, which can be produced using the method according to the invention, are much better than the prior art in terms of adhesion to the sheet, in terms of reproducibility, in terms of high electrical conductivity and good formability.

The layers are chromate-free and can be produced in all layer thicknesses, no changes in the MAK value sheet processing are necessary, since no chromate is processed. There are also no waste problems with regard to sludges, water, etc., as they occur in the known prior art. The aforementioned electrical conductivity is a prerequisite for the welding applications of today's manufacturing techniques. This is now possible because of the absence of aluminum oxide skin, which was removed in the dry etching station 7 and no longer forms in previously known dimensions under an inert gas atmosphere. From today's point of view, thin layers with a layer thickness of less than 1 µm are considerably more advantageous than conventional layer thicknesses of more than 2 µm; in particular, the undermining of the coating has not been observed when using a PVD technique. The morphologies of the PVD layers differ from those of galvanically or melt-immersed coatings as follows. Zn layers produced using vacuum technology have hexagonal platelet structures. In contrast to galvanic layers, the crystals are approximately parallel to the substrate surface and, depending on the coating temperature or deposition temperature, are 0.1 to 2 µm in size. Chemical analyzes show traces of organic components in galvanic coating, which are caused by the addition of e.g. B. nucleating agents, leveling aid fen and the like. To be installed in the layer. Zn layers made from the melt are significantly coarser than Zn layers produced by vacuum technology (by a factor of 2 to 20). In the case of mixed deposits produced using melting technology, disadvantageous bluish cabbage structures can arise.

In general, the PVD process, i.e. H. through the Be layers from the physical vapor phase a defi nier layer or several layers can be applied, wherein both the layer thickness and layer combinations and layer composition are variable. Compared to the known prior art, namely wet chemical Ver there are no driving or tribochemical processes Change in the structure or morphology of the sheet metal upper surface by chemical etching or physical deforma tion by rays. Also arises compared to the be knew prior art an increased reproducibility availability, for example with regard to liability. As already mentioned, there is a significantly lower order world pollution (waste water problem) especially against over chromate layers. They also still deliver today Chen coating process insufficient results in With regard to electrical conductivity, in particular in subsequent welding applications. Since similar Problems even with hot-dip galvanizing occur, a PVD coating is demge compared to much cheaper. As a special advantage adhesive PVD coating in series production Aluminum sheet can be applied described in the present invention.

Claims (8)

1. A method for coating an aluminum sheet with zinc and manganese by physical vapor deposition, characterized in that the sheet is dry-etched by means of plasma etching in an inert gas atmosphere at a negative pressure of 1 mbar to 1 µbar, that aluminum is subsequently vapor-deposited as an inorganic bonding agent layer and then a zinc -Man gan mixed layer or a multilayer with manganese as a top layer is applied, the zinc component being provided by thermal sources and the manganese component by anodic or cathodic arc discharge sources, by cathode sputtering or by electron beam evaporation. 2. The method according to claim 1, characterized in that in connection with the on vaporize the manganese portion near the substrate a plasma is produced. 3. The method according to any one of the preceding claims, characterized in that the sheet ( 1 ) lined up, partially sealed off from the environment processing zones ( 4 , 7 , 8 , 9 ) in which different pressure ratios prevail according to the respective processing step, and between which pressure locks ( 6 a, 6 b, 6 c, 6 d) are provided, the first processing zone a cleaning zone ( 4 ), the second a dry etching station ( 7 ), the third the coating zone ( 8 ) and the fourth processing zone a post-treatment zone ( 9 ) is. 4. The method according to any one of the preceding claims, characterized in that in the post-treatment zone ( 9 ), the layer applied in the coating zone ( 8 ) is thermally stabilized and the substrate (sheet 1 ) is cooled in an argon or nitrogen mixed with th atmosphere. 5. The method according to any one of the preceding claims, characterized in that in the aftertreatment zone ( 9 ) a further protective layer is sprayed on, for example, or is applied to form by plasma polymerization. 6. The method according to any one of the preceding claims, characterized in that the sheet ( 1 ) before or when entering the dry etching station ( 7 ) is heated in particular inductively. 7. The method according to any one of the preceding claims, characterized in that the sheet ( 1 ) coming from a solution annealing furnace is deterred before entering the dry etching station ( 7 ). 8. The method according to any one of the preceding claims, characterized in that in the coating zone ( 8 ) to the sheet metal ( 1 ) a negative voltage is applied relative to the chamber sealing off the coating zone from the environment.