DE102017011557A1 - Coating for a body part with an alloy of zinc and manganese, body part with such a coating and method for producing a coated body part with such a coating - Google Patents

Abstract

The invention relates to a coating (3) for a body part (1), wherein the coating (3) comprises an alloy, and wherein the alloy comprises zinc and manganese. In this case, the alloy has a concentration gradient (5) of manganese, wherein the proportion of manganese in the alloy in the direction of a side (7) facing away from the body part (1) of the coating (3) to a side facing the body part (1) ( 9) of the coating (3) decreases, and wherein the alloy has a proportion of manganese on the body part (1) facing away from the side (7) of at most 40 wt .-%.

Description

The invention relates to a coating for a body part with an alloy of zinc and manganese, a body part with such a coating and a method for producing a coated body part with such a coating.

To improve the durability of body parts, in particular body parts made of steel, the body parts are provided with a corrosion protection coating both for cold workability and for hot workability. In order to increase the corrosion resistance of body parts, in particular to ensure good corrosion protection properties, the body parts are usually coated with a metallic coating. Hot dip galvanized or electrolytically galvanized coatings have become established for body parts. These coatings provide cathodic corrosion protection because of the low corrosion potential based on a zinc-based layer compared to body parts without such a layer. In addition, good properties for the subsequent painting and joining processes can be achieved by this coating.

The advantage of zinc-based corrosion coatings is that they not only have a barrier effect with the formation of corrosion products, but also provide an active cathodic corrosion protection for the body part. However, pure zinc corrosion coatings also have disadvantages; In particular, it is known in direct press-hardening of zinc anticorrosive coatings that macro- and microcracks can occur in the steel.

Numerous zinc alloys for coatings are known, for example zinc-nickel, zinc-manganese, zinc-iron, zinc-aluminum, zinc-magnesium and zinc-aluminum-magnesium, which have better properties than pure zinc coatings. There are zinc-iron coatings known that are well suited for the joining technique. However, zinc-iron coatings have lower corrosion resistance than pure zinc coatings because the corrosion potential of zinc-iron coatings is increased compared to pure zinc. Furthermore, the high iron content in the coating leads to higher risks of red rust formation on the surface of the coating, which affects the optical quality as well as the long-term corrosion stability of the product. In the case of zinc-magnesium and zinc-aluminum-magnesium coatings, advantageous corrosion protection properties are to be expected owing to the formation of particularly stable corrosion products.

From the international patent application with the publication number WO 2015/027972 A1 Zinc-based corrosion protection coatings for steel sheets are known, which are applied by hot dip method, wherein the coating in addition to a zinc content of at least 75 wt .-% impurities of 0.5 to 15 wt .-% manganese and 0.1 to 10.0 wt. -% aluminum.

From the international patent application with the publication number WO 2015/149918 A1 are known components for a motor vehicle, comprising a made of a hot-forming steel base body, which is provided with a zinc-containing coating, wherein the coating of an alloy of zinc-cobalt-manganese, zinc-cobalt or zinc-manganese is formed, and a Method for producing such a component.

The invention has for its object to provide a coating for a body part with a zinc-based alloy, a body part with such a coating and a method for producing a coated body part with such a coating, said disadvantages do not occur, and in particular a Increasing the corrosion protection of the body part is achieved in comparison to conventional zinc-based coatings, wherein also preferably the paint adhesion, the phosphatability, the availability and the processability in the cold and hot forming compared to known zinc-based coatings are improved.

The object is achieved by the objects of the independent claims are created, advantageous embodiments will become apparent from the dependent claims.

The object is achieved in particular by providing a coating for a body part, wherein the coating comprises an alloy, and wherein the alloy comprises zinc and manganese. The alloy has a concentration gradient of manganese, wherein the proportion of manganese in the alloy in the direction of one of the body part side facing away from the coating toward a body part facing side of the coating decreases, and wherein the alloy has a proportion of manganese on the side facing away from the body part of at most 40 wt .-%.

The coating has advantages over the prior art. Advantageously, due to the coating according to the invention, in particular due to the creation of a concentration gradient of manganese in the alloy, the proportion of manganese in the alloy decreases as intended in the direction of a side of the coating facing away from the body part to a side of the coating facing the body part, achieved an increase in corrosion protection, in particular, a local corrosion is reduced. Advantageously, improved coating adhesion and improved phosphatability of the coating are achieved by the coating according to the invention. The coating according to the invention permits improved cold working and / or hot working in the production, in particular in that less macroscopic and / or microcracks are produced in the coating according to the invention and in the substrate. The zinc and manganese alloy coating of the present invention is a zinc-based protective layer which provides cathodic corrosion protection, particularly by forming stable corrosion products with a low dissolution rate after the formation of zinc-manganese intermetallic phases compared to conventional zinc-manganese. based coatings, which are located by the inventive concentration gradient of manganese in the alloy advantageously on the side facing away from the body part of the coating. Thus, an improved anticorrosive effect can be obtained because the concentration gradient of manganese in the alloy is such that the content of manganese in the alloy of the coating is lowest on the body part and on the surface of the coating in contact with air. is highest. Advantageously, the coating of the invention allows the formation of a particularly thin coating, which leads to a saving of cost and weight in the corrosion protection of the body part. Preferably, a further coating comprising a different alloy can be applied to the coating according to the invention.

A body part is understood to mean, in particular, a part of the bodywork of a vehicle, preferably a passenger car, lorry, bus, motorhome, construction vehicle, commercial vehicle or rail vehicle, boat, ship or aircraft.

According to one embodiment of the invention, it is provided that the alloy has on the side facing away from the body part a proportion of manganese of at most 40 wt .-%, preferably of at most 35 wt .-%, preferably of at most 30 wt .-%, preferably from at most 25 wt .-%, preferably of at most 20 wt .-%, preferably of at most 15 wt .-%, preferably of at most 10 wt .-%, preferably from 10 to 40 wt .-%, preferably from 10 to 35 wt .-%, preferably from 10 to 30 wt .-%, preferably from 10 to 25 wt .-%, preferably from 10 to 20 wt .-%, or preferably from 20 to 30 wt .-%. In this area, the already mentioned advantages are realized in a special way.

According to one development of the invention, it is provided that the alloy has a proportion of manganese of not more than 5% by weight, preferably not more than 4% by weight, preferably not more than 3% by weight, preferably not more than 2, on the side facing the body part Wt .-%, preferably at most 1 wt .-%, preferably at most 0.8 wt .-%, preferably at most 0.6 wt .-%, preferably at most 0.4 wt .-%, preferably at most 0.2 wt. -%, or preferably at most 0.1 wt .-%. Particularly preferably, the alloy has no or almost no manganese on the side facing the body part. In these areas, the already mentioned advantages are realized in a special way.

The coating preferably has a proportion of manganese of at most 30% by weight, preferably at most 20% by weight, preferably at most 15% by weight, preferably at most 10% by weight, preferably 10 to 20% by weight. , preferably 5 to 15 wt .-%, preferably 1 to 15 wt .-%, preferably 1 to 10 wt .-%, or preferably 1 to 5 wt .-%. In this area, the already mentioned advantages are realized in a special way.

According to one development of the invention, it is provided that the coating has a proportion of zinc of at least 60% by weight, preferably at least 70% by weight, or preferably at least 75% by weight. In this area, the already mentioned advantages are realized in a special way.

• - mindestens 0,1 Gew.-% bis höchstens 10 Gew.-% Aluminium,
• - mindestens 0,1 Gew.-% bis höchstens 10 Gew.-% Chrom,
• - mindestens 0,1 Gew.-% bis höchstens 10 Gew.-% Eisen,
• - mindestens 0,1 Gew.-% bis höchstens 10 Gew.-% Kobalt,
• - mindestens 0,1 Gew.-% bis höchstens 10 Gew.-% Magnesium, und
• - mindestens 0,1 Gew.-% bis höchstens 10 Gew.-% Nickel.

According to one development of the invention, it is provided that the alloy has a proportion of at least one further element selected from the group consisting of:

• at least 0.1% by weight to at most 10% by weight of aluminum,
• at least 0.1% by weight to at most 10% by weight of chromium,
• at least 0.1% by weight to at most 10% by weight of iron,
• at least 0.1% by weight to at most 10% by weight of cobalt,
• at least 0.1% by weight to at most 10% by weight of magnesium, and
• - At least 0.1 wt .-% to at most 10 wt .-% nickel.

In this area, the already mentioned advantages are realized in a special way. Other elements may be sulfur, lead, copper, molybdenum, titanium, zirconium or manufacturing impurities, in particular unavoidable impurities. Unavoidable impurity preferably occurs in a proportion of at most 0.2% by weight, preferably at most 0.1% by weight.

According to a development of the invention, it is provided that the coating has a layer thickness of at most 200 μm, preferably at most 100 μm, preferably at most 80 μm, preferably at most 60 μm, preferably at most 50 μm, preferably at most 40 μm, preferably at most 30 μm at most 25 μm, preferably at most 20 μm, preferably between 1 and 100 μm, preferably between 1 and 80 μm, preferably between 1 and 50 μm, preferably between 1 and 40 μm, preferably between 1 and 30 μm, preferably between 1 and 20 μm , preferably between 10 and 100 μm, preferably between 10 and 80 μm, preferably between 10 and 50 μm, preferably between 10 and 40 μm, preferably between 10 and 30 μm, or preferably between 10 and 20 μm. In the embodiments mentioned here, the advantages already described are realized in a special way.

According to a development of the invention, it is provided that the coating has at least two layers with different proportions of manganese. The coating preferably has at least 3 layers with different proportions of manganese, preferably at least 4 layers, preferably at least 5 layers, preferably at least 6 layers, preferably at least 10 layers, preferably at least 20 layers, preferably at least 50 layers, or preferably at least 100 layers. Preferably, the layers have different layer thicknesses. In the embodiment mentioned here, the advantages already described are realized in a special way.

The proportion of manganese in the alloy preferably decreases from at least 5% by weight, preferably by at least 8% by weight, from one layer of the coating in the direction of the side of the coating facing away from the body part to an adjacent layer of the side facing the body part. %, preferably by at least 10% by weight, preferably by at least 15% by weight, preferably by at least 20% by weight, preferably by 1 to 50% by weight, preferably by 5 to 50% by weight, preferably by 10 to 50 wt .-%, preferably by 1 to 30 wt .-%, preferably by 5 to 30 atomic%, or preferably by 10 to 30 wt .-%, wherein the indication wt .-% based on the total amount of metals in the alloy. In the embodiment mentioned here, the advantages already described are realized in a special way.

According to one embodiment of the invention, it is provided that the proportion of manganese in the coating decreases continuously from the side facing away from the body part to the side facing the body part. A continuous decrease in the proportion of manganese in the coating is preferably understood to mean that the proportion of manganese does not change abruptly, but rather curvilinearly, in particular steadily, preferably continuously and differentiably, more preferably linearly, over the layer thickness embodiment mentioned above realize the advantages already described in a special way.

According to one embodiment of the invention, it is provided that the proportion of manganese in the coating decreases discontinuously from the side facing away from the body part to the side facing the body part. Preferably, the proportion of manganese changes abruptly from one layer in the direction of the side of the coating facing away from the body part to a layer in the direction of the body part facing side of the coating. Preferably, the proportion of manganese in the coating gradually decreases from one layer in the direction of the side of the coating facing away from the body part to a layer in the direction of the side of the coating facing the body part. Preferably, a layer between two layers adjacent to the layer may have a higher or a lower amount of manganese compared to the adjacent layers.

The object is also achieved by providing a body part with a coating according to the invention, in particular according to one of the previously described embodiments. In particular, the advantages which have already been explained in connection with the coating result for the coated body part.

According to a development of the invention, it is provided that the body part is made of steel, for example high-strength steel without interstitial atoms (HSIF), high-strength low-alloy steel (HSLA), dual-phase steel (DP), complex phases steel (CP), deformation-induced hardening steel ( TRIP), bake-hardening steel, ultra high-strength steels 22MnB5, or a similar steel grade.

According to a preferred embodiment of the invention, it is provided that the body part is completely coated with the coating according to the invention. According to a further preferred embodiment of the invention, it is provided that the body part is coated in regions, preferably on one side, with the coating according to the invention.

The object is also achieved by providing a method for producing a coated body part with a coating according to the invention having a concentration gradient of manganese, wherein in the process an alloy comprising zinc and manganese by a hot dip process, an electrolytic process, a PVD Method (Physical Vapor Deposition), a CVD (Chemical Vapor Deposition) method and / or an IVD (Ion Vapor Deposition) method for forming the coating is deposited on a body part, wherein the proportion of manganese in the alloy during deposition of the alloy increases, so that the coated body part with the coating with the concentration gradient of manganese is obtained. In particular, the advantages which have already been explained in connection with the coating and / or the body part with the coating according to the invention result in connection with the method.

Preferably, the alloy of at least one master alloy and / or the chemical elements is obtained by melting.

Preferably, the alloy is deposited in an electrolytic process from an aqueous electrolyte solution, in particular from a sulfate or chloride solution.

Preferably, an electric current density or potential is varied during the deposition, so that the proportion of manganese in the alloy can be varied. Incidentally, an increase in the current density leads to an increase in the proportion of manganese in the alloy and a reduction in the current density leads to a reduction in the proportion of manganese in the alloy.

• 1 eine schematische Darstellung eines Stahlsubstrats mit einer Beschichtung mit Konzentrationsgradienten; und
• 2 ein schematisches Diagramm des Anteils an Mangan in der Legierung in Abhängigkeit von einer elektrischen Stromdichte.

The invention will be explained in more detail below with reference to the drawings. Showing:

• 1 a schematic representation of a steel substrate with a coating with concentration gradients; and
• 2 a schematic diagram of the proportion of manganese in the alloy as a function of an electric current density.

1 shows a schematic representation of a steel substrate, in particular a body part 1 , with a coating 3 with a concentration gradient 5 of manganese. The body part 1 according to the embodiment shown here has a coating 3 with an alloy, the alloy comprising zinc and manganese. The alloy points inside the coating 3 a concentration gradient 5 on manganese, with the proportion of manganese in the alloy in the direction of one of the body part 1 intended side facing away 7 the coating 3 containing 20 to 30% by weight of manganese, to one of the body part 1 intended side facing 9 the coating 3 which has 0% by weight or nearly 0% by weight of manganese. By such a concentration gradient 5 of manganese in the coating 3 provides improved corrosion protection compared to pure zinc or zinc-manganese alloys without concentration gradients 5 receive.

In the present embodiment, the body part 1 opposite side 7 the coating 3 the highest proportion of manganese from 20 to 30 wt .-%, by the layer thickness down to the body part 1 facing side 9 the coating 3 decreases to a proportion of manganese of 0 wt .-% or nearly 0 wt .-%. The use of higher levels of manganese in the body part 1 opposite side 7 the coating 3 leads to a preferential corrosion of manganese-rich phases, which leads to an increase in the pH value and the formation of stable corrosion products. This significantly improves the corrosion protection compared to pure zinc. The use of a lower proportion of manganese in the body part 1 facing side 9 the coating 3 On the other hand, it leads to a low corrosion rate compared to zinc-based alloys with a high manganese content. By using an alloy with different proportions of manganese in the coating 3 optimal corrosion protection properties can be achieved.

In such a zinc-based alloy with a concentration gradient 5 on manganese behaves the body part 1 opposite side 7 the coating 3 as a sacrificial anode and protects the steel substrate, in particular the body part 1 , before the loss of functional properties, in particular against mechanical loads, for example in a crash. The manganese-rich phases of the coating preferably oxidize due to the low corrosion potential of manganese compared to zinc. The oxidation of manganese leads to the formation of Mn ²⁺ ions, which lead to an increase in the pH by hydrogen evolution. Due to the higher pH, corrosion products form at a low dissolution rate, resulting in the formation of a dense, stable and poorly soluble protective layer. This protective layer of corrosion products prevents or slows down the corrosion mechanisms on the body part 1 and the underlying layers. The coating according to the invention provides improved corrosion protection, at the same time the paint adhesion and the phosphatability are improved in comparison to known zinc-based coatings.

In this embodiment, the alloy has a continuous concentration gradient 5 of manganese in the coating 3 but the alloy may alternatively have a discontinuous concentration gradient 5 respectively. The use of a continuous concentration gradient 5 of manganese in the coating 3 is advantageous in that such coatings have good adhesion properties, thereby reducing the risk of delamination, adhesion defects, and lack of compatibility between metallic layers.

The use of other elements in the alloy, such as aluminum, chromium, iron, cobalt, magnesium and / or nickel, is conceivable. This allows further specific properties of the zinc-based alloy with concentration gradients 5 to be obtained.

2 shows a schematic diagram of the proportion of manganese in an alloy as a function of an electric current density in the deposition of the alloy on a body part 1 , in particular a body part 1 from steel. The coated body part 1 with a coating 3 with a concentration gradient 5 of manganese in the alloy (see 1 ) is obtained by depositing an alloy comprising zinc and manganese. The alloy is made by an electrolytic process on the body part 1 deposited. In particular, the alloy is deposited from aqueous electrolytes such as sulfate and chloride solutions, for example, chloride electrolytes having the following composition are used: 2.8 M KCl, 0.6 M MnCl ₂ , 0.075 M ZnCl ₂ , 0.32 MH ₃ BO ₃ , 0.5 gl ^-1 4-HB and 6.5 mM NH ₄ SCN.

The proportion of manganese in depositing the alloy depends on the current density used, the potential, the electrolyte composition and the deposition process. The profile of the manganese content in the alloy can be varied according to the application requirement and freely selected by using the above-mentioned deposition techniques, if the current density, the potential or the electrolyte is varied during the deposition of the alloy. Increasing the current density leads to an increase in the proportion of manganese in the coating. As a result, the proportion of manganese in the alloy during the deposition of the alloy increases while increasing the current density, so that the coated body part 1 with the coating 3 with the concentration gradient 5 is obtained on manganese. In this embodiment, the coating 3 with the concentration gradient 5 with a layer thickness of 50 μm, preferably of 20 μm, preferably of 7 μm, on the body part 1 deposited.

Overall, it turns out that with the coating proposed here with an alloy comprising zinc and manganese, the proportion of manganese has a concentration gradient 5 has, advantageous corrosion properties can be obtained.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2015/027972 A1 [0005]
• WO 2015/149918 A1 [0006]

Claims (10)

A coating (3) for a body part (1), wherein the coating (3) comprises an alloy, and wherein the alloy comprises zinc and manganese, characterized in that the alloy has a concentration gradient (5) of manganese, the proportion of manganese in the alloy in the direction away from a side (7) of the coating (3) facing away from the body part (1) towards a side (9) of the coating (3) facing the body part (1), and wherein the alloy contains a proportion of manganese on the side facing away from the body part (1) (7) of at most 40 wt .-%. Coating (3) after Claim 1 , characterized in that the alloy on the body part (1) facing away from side (7) has a content of manganese of at most 30 wt .-%. Coating (3) according to one of the preceding claims, characterized in that the alloy has no or almost no manganese on the side (9) facing the body part (1). Coating (3) according to one of the preceding claims, characterized in that the coating (3) has a zinc content of at least 60% by weight. Coating (3) according to one of the preceding claims, characterized in that the alloy has a proportion of at least one further element selected from the group consisting of: - at least 0.1 wt .-% to at most 10 wt .-% aluminum, - At least 0.1 wt .-% to at most 10 wt .-% chromium, - at least 0.1 wt .-% to at most 10 wt .-% iron, - at least 0.1 wt .-% to at most 10 wt. -% cobalt, - at least 0.1 wt .-% to at most 10 wt .-% magnesium, and - at least 0.1 wt .-% to at most 10 wt .-% nickel. Coating (3) according to one of the preceding claims, characterized in that the coating has at least two layers with different proportions of manganese. Coating (3) according to one of the preceding claims, characterized in that the proportion of manganese in the coating (3) from the body part (1) facing away from side (7) to the body part (1) facing side (9) decreases continuously , Body part (1) with a coating (3) according to one of Claims 1 to 7 , Body part (1) after Claim 8 , characterized in that the body part (1) is formed of steel. Method for producing a coated body part (1) according to one of Claims 8 or 9 with a coating (3) with a concentration gradient (5) of manganese according to one of Claims 1 to 7 , characterized in that an alloy comprising zinc and manganese is deposited on a body part (1) by a hot dip method, an electrolytic method, a PVD method, a CVD method and / or an IVD method, the proportion of manganese in the alloy increases during the deposition of the alloy, so that the coated body part (1) with the concentration gradient (5) coating of manganese is obtained.

Images