DE1521148B2 - Ferrous metal article with an aluminum-zinc alloy coating and method for its manufacture - Google Patents

Description

The invention relates to zinc-aluminum coatings on iron surfaces by hot-dip metallization, in which the coating is formed in a weld pool which has both a high aluminum content and a high zinc content.

In FR-PS 7 07 035 it is indicated that zinc-aluminum alloys, for. B. steel that contains 70 to 99% zinc, the remainder aluminum. The steel workpieces are First provided with a coating of zinc, on the surface of which the zinc-aluminum alloy should adhere.

Similarly, from GB-PS 8 76 032 a method for improving the resistance of steel surfaces is known to the attack of hot or cold water, according to the first after is conventionally galvanized, whereupon the steel workpiece is immersed in a bath of molten zinc-aluminum alloy with a content of 0.1 to 2.5% aluminum and 0.01 to 0.05% silicon is immersed.

Furthermore, an attempt was made to carry out thorough analyzes of the effects of various components, normally used in the manufacture of such coatings without one however, had recognized the full importance of adding additives.

Thus, in the literature reference "Stahl und Eisen", 77, 1957, No. 7, p. 436, the effects are examined, which are suitable for an iron surface by adding zinc, silicon, beryllium or tin alone or in part result in combination. The effects of various other elements are also given. The problem addressed is that with aluminum alone on the iron side, one is strong toothed alloy layer is obtained. It is emphasized that the addition of zinc at 12% is a There is a clear limit because the alloy layer builds up at higher zinc concentrations changes significantly by creating a loosened alloy layer instead of a dense one, which has a lot thicker than even the dense alloy layer that is formed in pure aluminum melts.

From DT-AS 11 38 603 a method is also known which, among other things, increases the pulling speed of metals with aluminum or aluminum alloys, with certain amounts of alkali metals being added to the coating bath.

leads to be. In addition to iron, the metals that can be coated include chromium, cobalt, molybdenum, nickel and - various others .. When coating with aluminum alloys, the aluminum content can be between more than 99 and about 50%, with the remainder being beryllium, cerium, chromium, copper, Cobalt, magnesium, molybdenum, silicon, titanium, vanadium, zinc, etc. can be singly or in groups. In so far as the known ¹ "methods address the problem underlying the present invention, they give the impression that an intermediate layer of zinc must be created before a good coating of aluminum-zinc alloy can be applied to steel, or that the addition of more than a very limited amount of zinc leads to the difficulty that the intermediate layer is undesirably thick.

The teaching conveyed by the DT-AS 11 38 603 gives in its general nature considerations However, it gives no indication of how an improved coating could be obtained how to achieve tight adhesion of an aluminum alloy with more than 30% zinc content.

The object of the invention is therefore to create firmly adhering and corrosion-resistant aluminum

Zinc coatings with high levels of both components directly on objects containing iron.

The invention relates to the metal object specified in claims 1 and 2 as well the method characterized in claim 3 for its production.

The metal object according to the invention is characterized by a thin, uniform iron guide Interlayer at the interface between the ferrous substrate and the coating. That Silicon promotes the formation of an adherent coating, suppresses the formation of an iron-bearing coating Interlayer at the interface between the base body and the coating and ensures that the intermediate layer formed is thin and uniform. Depending on your requirements, more than 3% silicon can be obtained on the aluminum content. As far as it was found, the silicon content of the

3 4

Coating has no effect on the corrosion resistance is heated to ^{almost 65O 0 C.} The oven is powered by the

stand of the coated object. Combustion products from natural gas and air in

The process for making the metal is heated against a ratio of 1: 8. Behind the stove

The prior art according to the invention is in particular for the strip on a roller 11 through a cam

Coating of steel strips and wires useful. 5 mer 12 performed, in which the temperature of the strip on

A thick intermediate layer at the interface be- decreases approximately 427 ⁰ C. In the chamber 12 is

see the steel strip and a non-ferrous, an atmosphere of 99% hydrogen.

protective coating metal would prevent the formation of the strip before it enters an over-

Promote cracks in the coating if the coated draft vessel 13 protects against oxidation. With the help of

Object is deformed. In addition, an io submerged roller 15 and 15 'will run over the strip

strong alloy with the coating metal in the case of strips conveyed through a molten bath 14, which is at a temperature

from thin dimensioning made of iron to a ratio temperature of 570 ⁰ C is kept. When leaving the

moderately large loss of base metal, as a result of which the bath runs the strip through two lower smooth

Metal of the base itself is weakened. Rollers 16 made of (unalloyed) steel with low carbon

leads a strong alloy at the boundary layer 15 through it. When the strip is vertical too

sometimes to an uneven coating, so that a roller 18 continues to run, its coating of

Surface appearance leaves a lot to be desired. quenched an air blower 17, and then

The coated article according to the invention is wound onto a roll 19, the strip. the

and the method of applying this coating to an iron strip speed is approximately 13.7 m / min

Applying the substrate is 20 seconds and the immersion time in the coating bath is about 4 seconds.

explained in more detail in connection with the figures. The total thickness of the coating on both sides of the

F i g. Figure 1 is a photomicrograph of a cross-section coated strip averaging 0.05mm.
by means of a coated steel strip, the coating of which is attached. During the preparation of the weld pool, preferably approximately 25% aluminum and approximately 74% zinc are used, with a degree of purity of at least _; . contains; 25 at least 99.5% of the following composition made up *

F i g. 2 is a photomicrograph of a cross-section turned over:

by a coated steel band, the coating of which is aluminum ~~ 99 65 ° /

approximately 35% aluminum and approximately 64% zinc p; _c = n πΊ ο ° /

contains; Silicon 013 ° /

F i g. 3 is a photomicrograph of a cross section 30 Manganese 0Ό1 /

by a coated steel strip, the coating of which is zinc 0Ό1 /

approximately 54% aluminum and approximately 44.5% zinc vanadium · 001 ° /

contains; Cadmium · - · - · · r 0 * 02%

F i g. 4 is a photomicrograph of a cross section of sodium 0Ό0Ι ° /

by a coated steel band, the coating of which is an- 35 ' ^{/ o}

approximately 70% aluminum and approximately 28% zinc. The zinc used for the melt has a

contains; Purity level greater than 99.99%.

F i g. 5 shows schematically the device with which the silicon is added to the bath in the form of an aluminum

the object of the invention is produced. nium alloy having the following composition

In the preferred method of enrobing 40, added:

a ferrous pad, e.g. B. a steel strip, silicon 12 00 ° /

the strip is first cleaned by a cleaning iron 0 * 33 /

sung pulled through, the remainder of the aluminum from its surface

Removes grease and dirt. The cleaned strip

is then introduced into an oven and placed on a temperature heated temperature, which is roughly that of the coating bath. Implementation of the method according to the invention. The strip is then immediately combined by rens in such proportions that the bath is connected A protective gas atmosphere melted in a bath approached 35% aluminum, 64% zinc and 1% silicon Metal conveyed, which contains essentially from 25 to 70%.

Aluminum, the remainder zinc. The temperature of the 50 From the cross section of the after the procedure of the bath If the object is slightly above the melting point, the object is the microphotodes Metal held; the exact temperature depends on the graph of fig. 2 recorded. The alloy of the amount of aluminum and zinc in the bath. layer between the coating and the metal of the

In detail, according to FIG. 5 a Bd. 1 of the underlay is so thin that it is 500 times as thin

flanged steel of 0.711 mm thick with a Koh- 55 magnification is almost indistinguishable.

fuel content of 0.06% and a manganese content. The microphotograph of FIG. 1 shows in 500 times

of 0.31% and with other, usually forehand enlargement, a cross-section through another

nen elements from a supply roll 2 of a coated article according to the invention, the

Cleaning container 3 supplied, which is an aqueous Lö- as a strip of carbon steel (unalloyed steel)

Solution 4 of an alkaline cleaning solution for steel 60 according to the method explained above in a bath

strip in a concentration of 29.9 g / l, is coated, which is approximately 25% aluminum, 74%

which contains zinc and 0.77% silicon at a temperature of approximately 82 to 94 ° C. In this example

is held. The cleaned strip is made of is no visible alloying of the iron with

Brushes 5 scrubbed and present in a container 6 with the coating metal.

Rinsing water 7 rinsed off. From the rinsing container 6, 65 becomes. If the aluminum content of the coating is over 35%

the strip is increased by rubber squeegees 8 and beyond, a small amount of material occurs

Guide rollers 9 guided down through a furnace 10, as an alloy boundary layer in appearance. Self

in which the strip is at a temperature of- when the aluminum is 70% of the alloy coating

the intermediate iron-bearing layer at the Table I interface is uniform and thin. As uniform Let us denote an alloy layer that is almost even with a flat base, but the local one Projections in the zinc-aluminum coating can contain 5. This with larger amounts of aluminum Occurring uniformity of the intermediate layer can be seen in Figs. 3 and 4 see that in 500 times Enlargement show the cross-section through a similar steel, which according to the previously described ver io driving is overdone. When producing the sample according to FIG. 3 contains the bath with which the coated The article manufactured is approximately 54% aluminum, 44.5% zinc and 1.5% silicon while to produce the sample according to FIG. 4 approximately 15 70% aluminum, 28% zinc and 2% silicon are used.

In all examples according to FIGS. 1 to 4 is made with a solution of 95% amyl alcohol and 5% nitric acid Etched for 5 seconds.

The operating temperature of the coating bath is normally in the range of 524 to 678 ° C; depending on the amount of aluminum in the alloy, the temperature becomes with increasing Increased aluminum content.

Typical examples of the preferred bath temperatures, which change with the aluminum content are:

Type of coating Time in hours up to 1% rust 0.025 mm each Coating thickness 1. Hot-dip galvanized 325 2. Zinc-aluminum coating 2290 with approximately 25% Al 3. As 2. with about 35% Al 3234 4. As 2. with about 45% Al > 3805 *) 5. As 2. with about 54% Al > 3405 *) 6. As 2. with 70% Al 940

*) Attempt not completed.

Content of aluminum Approximate minium Bathroom tempera door in % in ⁰ C 25th 535 35 589 45 623 54 643 70 670

In the so-called exhaust test, the corrosion resistance of the products according to the invention is measured a content of 25 to 70% aluminum in the coating is far better than that of the hot-dip galvanized objects

so fulfilled.

In the exhaust test, two coated samples measuring 5.08 χ 10.1 cm ^{2 are} immersed for 8 s at a solution temperature of 82 ° C. in an aqueous solution of 0.05 η-sulfuric acid and 0.01 n-hydrobromic acid. At the end of the immersion time of 8 seconds, the samples are taken out and hung in the vapors of the immersion solution for 1 hour. This procedure is repeated every hour (a total of 20 times), after which the samples are held in a laboratory oven at 260 ° C. for 2 hours to complete the 24 hour cycle. The samples are then examined for the beginning of roasting *, rusting at the cut edges of the samples being disregarded. The entire experiment lasts 13 cycles of one day each.

The results of the exhaust test are in the tables listed:

Table II

The coatings produced by the process described above are metallurgically similar to the ferrous ones Document bound.

The coated articles according to the invention have numerous beneficial properties, such as the following Show data.

In the entire coating range from 25 to 70% aluminum results in the coated objects according to the invention, compared to hot-dip galvanized objects, superiority in a salt spray test, which was carried out according to A.S.T.M. method B 117-62, in the order of magnitude of approximately 3: 1 to 8: 1.

Typical results (average of four samples of size 10.1 × 15.2 cm ² with protected edges) are given in the following table for the salt spray tests on a hot-dip galvanized steel sheet and on steel sheets according to the invention with zinc-aluminum coatings are provided.

In terms of their external appearance, the coated articles according to the invention are small in size Tinsel on. This peculiarity is extremely desirable in numerous jobs, if an additional one Surface treatment, e.g. B. the application of paint is necessary. In the coating area with 25 to 45% aluminum, the surface of the object has an exceptionally smooth, white appearance.

Art of the coating Cycles by Start of roasting _:. the steel base *) ⁴⁵ 1. Galvanized 6th 2. Zinc-aluminum coating 12 to 13 with about 25% Al 3. Like 2. with about 35% Al 13th 4th Like 2. with about 45% Al 13th 5 ° c Like 2. with about 54% Al 13th 6th Like 2. with about 70% Al 13th

*) The rusting of the cut edges of the samples is not taken into account.

The objects according to the invention, the coating of which contains 25 to 70% aluminum, meet bending tests the requirements of A.S.T. M.-Norm A 93-59 T. Furthermore, show the objects according to Invention of flanging the edge flat in a corresponding standard test at all aluminum concentrations no peeling in the coating from 25 to 45%. The 70% aluminum coating shows some local flaking.

Furthermore show the objects according to the invention

dung, the coating of which contains 25 to 45% aluminum, only slight cracking when it is flat by 180 ° to be bent back on itself.

The suppleness and the adhesion of the coatings

are with the objects according to the invention an aluminum content of 25 to 70% in such a way that this allows for the customary deformation, e.g. B. the training of beading, bending, etc., without forming significant cracks or scales.

In summary, the ferrous objects that are coated with zinc-aluminum, with an aluminum content of 25 to 70% of the entire coating has a corrosion resistance similar to that of the hot-dip galvanized items is superior. The coatings and their aluminum content stand out within the wide range 25 to 45% due to its suppleness and freedom from flaking or flaking off when they are subjected to severe deformation processes; the coatings with an aluminum content draw from 40 to 60% of the total coating

are distinguished by their remarkable resistance to corrosion, that of the coatings by hot-dip galvanizing is far superior, although the ductility is at the upper end of the aluminum content range something is lost.

. Examples of articles to which the zinc-aluminum coatings described above can be easily applied are wires, fittings and forms of construction.

ίο Even if the covers for the items are in accordance with the invention consist essentially of the metals zinc and aluminum, so the coating also contain up to 0.3% chromium in order to influence the corrosion between the grain boundaries.

All percentages related to the components of the bath or coating relate look at the weight.

For this purpose 3 sheets of drawings

509 538/298

Claims (3)

Patent claims: 1. Ferrous metal object with an aluminum-zinc alloy coating consisting of 25 to 70 percent by weight aluminum and the remainder consists essentially of zinc and between the and an intermetallic intermediate layer is formed on the ferrous core, characterized in that that the intermediate layer at the lowest value for the aluminum content in the coating is so thin that it is at 500X magnification of the cross-section of the metal object remains invisible and that silicon in the coating in an amount of not less than 0.5%, preferably about 3%, by weight the aluminum content. 2. Metal object according to claim 1, characterized in that the coating for influencing the intergranular corrosion contains up to 0.3% chromium. 3. Process for the production of a metal object coated by hot metal plating according to Claim 1 or 2, according to which the surface of the object to be coated optionally of Grease and dirt are freed, the object to be coated is preheated and through a protective gas atmosphere through into the melt bath of the composition maintained at a temperature of 524 to 678 ° C 25 to 70% aluminum, the remainder - in addition to other alloy additives such as chromium and silicon - essentially zinc and- is immersed for a few seconds,. 'characterized in that the on approximately Bath temperature preheated object for about 4 s in that not less than 0.5% and especially about 3% silicon, based on the aluminum content, and optionally up to 0.3% Chromium-containing weld pool is immersed.