DE1521317A1 - Protective cover - Google Patents

Description

Inland Steel Company, Chicago, Illinois / V.St.v.A.

Protective cover

The invention relates generally to an improved protective magnesium-zinc alloy coating, and more particularly to a method for the production of an improved protective coating from a magnesium-aluminum-zinc alloy and an iron object that has a novel protective coating made of a magnesium-aluminum-zinc alloy wearing._

Zinc coatings have long been used to protect iron surfaces against corrosion. Various alloy metals were made added to the molten zinc to improve the properties of the metal coating or to improve the coating process. The alloy metals added to the zinc melt became common added in very small amounts, from a fraction of a percent to about 1 percent, and served limited improvement the corrosion resistance and the appearance of the coatings

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or to reduce the amount of intermetallic formed Links. The metals that have been added to a zinc bath include lead, tin, aluminum, cadmium, * antimony, and magnesium.

It has already been recognized that the coating has its best corrosion resistance when the magnesium concentration in the molten zinc is about 0.14-0.30 wt.%, Preferably 0.04-0.05%. It was also stated that the addition of more than about 0.1% by weight of magnesium to a zinc melt to be applied by immersion causes considerable processing difficulties, e.g. high loss due to large flux consumption and considerable ash formation on the surface of the bath so that an addition of aluminum up to a maximum of about 0.02 %, preferably about 0.005%, was recommended in order to reduce these losses and improve the appearance of the coating. Alloys increase the corrosion resistance to about 20-90%, on average by about $ 50, compared to normal zinc coatings An intermetallic layer is formed and annoying black particles are formed, which are disruptive during the coating process. Thus, there is still a need to improve a zinc alloy protective coating and the method for making it. ·

object

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The invention is an improved method for Coating a metal base with an improved protective zinc alloy coating.

Another object is a metal article bearing an improved protective zinc alloy coating.

Another object is an improved immersion bath made of magnesium-aluminum-zinc alloy for coating a metal substrate.

Further goals emerge from the following description and claims.

It has been found that a protective coating made of a metal alloy with considerably improved properties can be produced on a metal base, for example made of iron or iron alloy, by applying an alloy coating, which is about 1 - 4 wt .- ^ b magnesium and preferably about. 0.05 * ■ 5 »0 wt .- ^

Contains aluminum, the remainder zinc. If there is already an improvement te magnesium-zinc alloy with about 1 - 4 S ^ magnesium becomes when you add a very small amount of aluminum to the alloy bath It has been found that the corrosion resistance and other properties of the coating can be significantly improved when the alloy is about 1-4 wt.> 4 magnesium and preferably contains about 3-5 wt .- / o aluminum and the bed is made of zinc, f

if

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When the improved alloy coatings of the invention have If an iron base is applied, they have extremely good corrosion resistance. The values in Table I below show the significant improvement in the corrosion resistance of a relatively * thin material by immersion in alloy coating applied to the melt, which contains magnesium, aluminum and zinc within the concentration ranges, which were specified according to the invention, compared to a conventional zinc coating applied by immersion in the melt Similar strength to that with a known zinc alloy in the usual continuous process by immersion in the melt has been made "

Table I. Average overtime to disintegration

Toeammenwetting the Zugsgewioht each ' disturbance in 5 $ igem cover bath side (g / 929 cm) Salsnebel (hours)

1) Zinc alloy auditoriums

2) 3 * Mg + Zn

3) 4 i » Mg + 0.2 # Al + Zn

4) 2.5 # Mg + 4.4 ^ Al + Zn

Each of the magnesium-zinc alloys according to the invention melts well below the melting point of a conventional zinc coating alloy (421 ° C.). The melting point of the eutectic tremie before magnesium and zinc, date 3 Ί » magnesium contains, is, for example, 367 C, and a coating mass of 2.49 wt .- # magnesium,

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15.0 336 14.2 2028 14.2 2028 15.0 > 4000

Constitutes 4.39 wt. ° -f aluminum, balance zinc with a 338 ° G-melting eutectic. The other alloys within the range specified according to the invention have melting points between about 343 and 40 ° C. If so desired, it is possible to use a coating bath significantly below the normal operating temperature of a conventional zinc electroplating bath, which is between about 427 ^{and <} 455 ° C , to work.

The values in Table II below show how much intermetallic Connection is formed when coatings are immersed in Melts of the specified composition can be produced at the specified temperatures:

ί Mg zinc Zn O, the i> Tabel II Strength of inter W. Mg + Zn 0, ⁰ Io temperature metallic 12.7 Mg + Zn 0, Ί * the Schmel layer 1.01 r5 Mg + Zn + , 4 melt ze ( ⁰ C) 2.54 , 5 Mg + Zn + + , 4 460 under 5.08 Mg + Zn + 400 - 7.62 Mg + Zn + 2 417 1.01 ft ι + + Zn 2 438 1.01 Ig + Zn 2 '455 under 1.01 io mg 4th Al 400 under 1.01 4th Al 427 under 1.01 Al 455 under / oAl 400 under io Al 455 composition Heines 3 3 3 3 3 3 3 2, 2,

If the Söhntelze is kept at temperatures above 40 ° C, the addition of aluminum apparently inhibits the formation of intermetallics Links.

It was also observed that no significant intermetallic Layer on the contact surface between the alloy over-

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train and the underlying iron is formed if the invention Sinter immersion bath is maintained at a temperature between the melting point of the alloy and 455 C. The educated Protective coating has improved physical properties, e.g. better drawability and deformability, because it is practical does not contain a layer of brittle intermetallic compounds. .

Further savings can be made when applying the coating Immersion in the melt by increasing the aluminum content £, -> can be made in order to reduce the skimming losses that normally occur by oxidation of the bath 'arise on the surface,' especially at higher temperatures. The values in Table III show the results of skimming tests carried out in a vessel stainless steel at 455 C.

Table III

amount of

Duration of the educated

Temperature * static scoop composition of the bath of the bath (C) Try the product

jfo Mg + Ö _r 2 $ Al +. Zn 2.5 ^W / S Mg + 4.4 # -Al + Zn

It has also proven advantageous to use the improved Magnesium-zinc alloy coating according to the invention to cool rapidly when the coated article is removed from the coating bath to get a smoother and more appealing surface. Aenn the egg article with the inventive Do not remove the cover immediately after removing it from the immersion

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455 4th hours 145 G G 455 4th hours 39 , 5

bath is cooled rapidly, the surface becomes irregular and something speckled. These surface defects become essential reduced when a flowing coolant, e.g., gaseous nitrogen, is allowed to act on the surface of the alloy as soon as the object is taken out of the coating bath to thereby effect rapid cooling.

The following examples illustrate and limit the invention but not.

example 1

A row * of 10.2 20.3 µm steel specimens were made from 20 gauge fully hardened steel that was 0.86 mm thick and about 0.04 # G, 0.29-0.35 # Mn, 0 .01 0.011 i » P, 0.019-0.020 i» S and 0.04 i » Cu, the remainder being iron. All plates were pre-cleaned by oxidation according to the following process (1) cold greasing for 15 minutes with triohloräthylendaepf at 77 ° C. and (2) oxidation for 30 seconds in an oven at 899 ° C. The oxidized plates were then transferred to a drying chamber, ie a laboratory - Electroplating device included. The atmosphere in the chamber contained 10 $ hydrogen, the remainder nitrogen. The dew point in the drying chamber was kept below -26 ° C. The cleaned plates were preheated to 982 ° C. for 3 minutes and then cooled to the bath temperature for immersion.

An alloy containing 3% by weight magnesium and 97% zinc, was melted in a graphite crucible at about 400 g '· one

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BATH

Experiments were carried out with the zinc alloy, where the bath temperature was varied between 400 and 455 C »The Immersion time was about 5 seconds. The effect of the deeper The bath temperature on the thickness of the intermetallic layer can be seen from the following values:

Table IV * 01 , 35 J Bath temperature (θ) Strength of 54 .62 81 400 416 intermetallic layer 427 438 1, 455 2, 08 - 6 3, 35 · 5, ■ 7 6,

Table V shows the results of a series of spray tests with 5% saline solution with the zinc alloy coatings applied as above.

Table V Spray tests with steel coated with Mg-Zn alloy

- $> Al in number
look for the leather
alloy plates.

Thickness of the coating

0.20

4th
5
6th

19.3-25.4 22.9-25.4 22.9-40.6

18.8-50.5

Time to rust

Area \ Medium
(Hours)

1968-2616
2184-2496
I992-3OOO
1848 ^ 3000

2522
23OO
27OO
2610

Averages 2483

Normal GaI vanization

264 336

288 2Θ8

294

From the results of the Saizsprühveruche in Table V it can be seen that with a coating thickness in the range of 35.4 g

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BATH

for every 929 cm, the average durability of the plates coated with 3% Mg-containing zinc alloy was 230 hours compared to 300 hours for the normally galvanized steel plates. The alloy coatings according to the invention have almost eight times the resistance of normal galvanized coatings.

2 tensile strength was greater than 35 »4 g per 929 cm, the average durability was 2655 hours. The aluminum does not appear to have any effect on the durability of the salt spray. In experiment 3, for example, the average durability of the coatings made of aluminum-free alloy was 2700 hours, while that of the coatings made of an alloy of 3 ° β> Mg, 0.2% Al, best zinc, was 2610 hours. The latter coatings also had satisfactory adhesiveness and deformability when the coating was produced with baths of 400-455 ° C. Furthermore, the color properties of the coatings made from the ^{zinc alloy containing 3 J} ß> Mg are comparable to those of galvanized steel and are satisfactory.

Example 2

A common steel bath for a hot mill with a thickness of about 2.03 mm is cold on a five-section tandem mill to a thickness of about 0.6 mm (2-4 gauge). The completely hardened 0.6 mm thick strip, which has a Rookwell hardness (30-T scale) of about 80, is made by means of a continuous Cleaning line cleaned and then left in a chamber, to eliminate the loss of ductility in cold rolling

run.

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run. The tempered strip is then tempered by rolling sent to duroh a suitable surface for coating To create immersion.

The tempered steel strip is then put into a bath of a immersed in molten magnesium-zinc alloy of the following composition:

Mg 2.77 U ew. Fe 0.01 Il Pb 0.013 It Zn 97.207 Il

While the alloy bath was kept at 400 ° C., the Steel strips at a speed of about 8.54 m per minute sent into the bath at an angle of about 70 to the horizontal. The strip was about 5 seconds (no more than 10 seconds) left to linger in the bath and continuously removed at an angle of about 90 ° to the horizontal by coating rollers. ■ The coating rollers were covered by a flame in order to be carried away Retain oxide fractions from the bath. When taking out of the coated strip from the bath, the coating was rapidly cooled by blowing air below 1.05 kg / cm. The coating had a thickness of between about 23 and 53 u on each side of the strip The coating had the same improved properties as that of Example 1>

Example 3

A tempered steel strip processed as in Example 2 was placed in a molten bath of 400 g in the same way

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immersed as in Example 2, the bath having the following composition had

Mg 2.97 Wt .- / o Fe 0.07 "Il Pb 0.013 Il Al 0.12 Il Zn 96.827 Il

The coated strip obtained has the same properties like that of example 2. The skimming losses were smaller than in Example 2, presumably due to the addition of aluminum.

Example 4

A series of 10.2 χ 20.3 cm sample plates made of steel was made from 20 gauge Sterken fully cured ütahlplatten mm with a thickness of 0.86 and containing about 0.4 $> C, from 0.29 to 0.35 $ Mn, 0.01-0.11 ^ P, 0.019-0.020 AS and 0.04 # Cu, remainder iron. All panels were pre-cleaned by oxidizing for 30 seconds at 899 ° C, and the oxidized panels were then transferred to the drying chamber which contained a laboratory electroplating device. The atmosphere in the drying chamber contained 10% hydrogen, the remainder nitrogen. The dew point in the drying chamber was always kept below -26 ° C. The cleaned plates were preheated to 982 G for 3 minutes and then cooled to the jade temperature for immersion,

j3 an alloy of about 2.49 wt .-? S Mg, 4.39 # Al, remainder zinc, vkurde melted in a graphite crucible at around 400C. Three Experimental series of plates were carried out at a bath temperature of 400, 427

respectively.

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455 C coated. The duration of the dew was in each case

about 5 seconds and the mean coating weight was 18.7 g

2
929 cm each. These sample panels were then deformed by punching a 25.4 n ™ diameter hole and the area around each hole pressed into a tubular part protruding 12.7 mm above the surface of the ¹ panel. Table VI shows the results of testing the panels by the standard 570 salt spray tests.

Table YI

Mean over- Mean time to weight depending on the rusting through Composition of the bath side (g / 929cm) (hours)

Normal anodized xzinc alloy

(Comparative sample) 18.7 380.

2.49 / o Mg + 4.39% Al '+ 93% Zn 18.7> 4000 (before the

formj

2149% ^M g + 4 »39% Al + 93% Zn 18.7 74OOO (after deformation)

From the. Results in Table VI can be seen that the alloy coating of Example 1, even after deformation, about 10 times the corrosion resistance of a normal electroplated coating Has. This alloy coating also has very satisfactory adhesiveness, good deformability and good color properties.

In addition to the specified improved properties of the new coatings made of ternary alloys, these alloys also have the advantage »of being able to be processed much better in a hot coating bath , όο, for example, the annoying black particles that occur in a coating alloy made of 3% Mg, 0.2% Al and

" Zinc

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Zinc are not formed, and the suction losses are much smaller even at a higher bath temperature. The lower losses with increased bath temperature make it possible to work within a wider temperature range, for example at the relatively high temperature of -455 C, if this is desired.

Example 5

A series of plates were produced and coated as in Example 1 by immersion in a hot coating bath of 2 % Mg, 4 % Al and 94 ° / ° Zn with a coating with an average weight of 9.4 g / 929 cm per side. When sprayed with a 5% saline solution, these test panels were corrosion-resistant (against red rust) for 2000 hours, compared to 175 hours for panels which had an equally heavy zinc coating produced by immersion. -

Example 6 '

A series of plates was ergestellt 3 and as in Example 1 by immersing in a überztigsbad from 2.4 ° / o Mg, 3.8 fo Al and 93.8 g io Zn with a coating having an average thickness of 11.6 per 929 om coated on each side. The test panels were resistant to the same corrosion test for 2000 hours, compared to hours for panels with a conventional dew coating of the same weight

Example 7

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Example 7

A series of plates were prepared and as in Example 1 by immersion in a coating bath of 2.4 ° Mg, 3.2 ° β> Al and 94> 4% Zn with a coating having an average weight of 11.0 g / 929 cm covered on each side. Die.Platten were in the specified corrosion test for 1600 hours resistant to 200 hours in the case of plates with a conventional immersion coating of the same weight.

Example 8

A series of plates was produced and, as in Example 1, by immersion in a coating bath of 2.5 ° 7 ° Mg, 4 ° 5 ° Al and 93 ° Zn with a coating having an average weight of 12.2 g

Covered 929 cm on each side. The plates were at the specified Corrosion test resistant over 160 hours in comparison 228 hours for plates with a standard zinc immersion coating of the same weight.

From the above .examples and test results it can be seen that that it is now possible to use a strip of Sisen with the same resistance to corrosion as usual to produce galvanized strips by using the improved alloys of the invention in far less Thickness than the usual coating can be applied. In accordance with the invention it also becomes possible to obtain a much longer corrosion resistance for an iron object,

when

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if a coating of the same weight as conventional zinc coatings is applied.

Of course, the novel alloy coatings according to the invention on a metal surface or the like. Also in a different way than by immersion in the melt as described here are applied, especially when very thin coatings in the Order of magnitude of about 2.8 g / 929 cm should be applied » For example, a thin alloy coating can be applied by vapor deposition can be applied by passing a steel strip continuously through a chamber in which a pressure of about 10 torr prevails and in the vicinity of the surface of the moving Strip a reservoir for the alloy is located in the form of grass, the condenses on the surface of the moving strip. Thin Alloy coatings can also be electrolytically obtained from a suitable one Salt bath or by using certain wiping methods on the Strips are applied leaving a hot immersion bath. The alloy coating according to the invention can also be carried out by powder metallurgy Method are applied, wherein a powdered alloy of the specified composition to a suitable paste deformed and applied into a thin layer, which is then converted into Usually cold reduced, sintered, rolled and heat treated will. -

üas'erfindürigsgeraässer "method can be used within the scope of the invention be modified in every possible way.

■ - ■ "-. ■ '- · - · ■■""-" -. "■■ -. ■ claims.

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Claims (15)

Claims 1. Method of coating a metal surface, thereby characterized in that a protective coating of a zinc alloy is applied to the surface, which is about 1 to 4 wt .- $ Magnesium contains 2. Method of coating an iron surface by Immersion in an alloy melt to increase corrosion resistance, characterized in that the iron surface is immersed in a bath of molten zinc containing about 1-4 wt .- ^ Magnesium contains, while the remainder consists essentially of zinc, to form a protective coating of magnesium-zinc alloy on the surface that has good corrosion resistance. 3 · Method of coating an iron surface, thereby characterized in that the metallic iron surface is immersed in a bath of molten zinc clay containing about 3 wt .- ^ magnesium contains, while the rest of the bath consists essentially of zinc 4 · Method of coating a metal surface, thereby characterized in that a protective coating is applied to the metal surface, which essentially contains about 1-4% by weight of magnesium and contains about 0.05-5 wt. $ aluminum, with the remainder im consists essentially of zinc » 90983 A / 05 3 2 BATH 5. A method for coating an iron surface duroh immersion in a hot alloy melt, characterized in that the metallic iron surface is immersed in a bath of a molten metal alloy containing about 1-3 wt .- $ magnesium und'etwa 3 * ^A 5 wt. -ji contains aluminum, while the rest of the bath consists essentially of zinc in order to produce a protective coating with good corrosion resistance on the surface. 6. Method of coating by dipping in a hot Alloy melt according to claim 5 »characterized in that the bath is kept at a temperature between approximately 343 and 455 ° C. 7 · A process for coating an iron surface by Eintauohen in a hot Legierungssohmelze, daduroh in that immersing the metallic surface in a molten iron bath containing about 2.5 parts by weight j6 magnesium, about 4.4 wt -. ^A / o aluminum and contains about 93 parts by weight of zinc. Θ. Object consisting of a base made of iron or an iron alloy and a coating made of a magnesium-zinc alloy, which contains about 1-4 wt .- ^ magnesium, during the It consists essentially of zinc 9 Object consisting of a base made of iron or an iron alloy and a coating made of a magnesium-zinc alloy, which contains about 3 wt .- ^ magnesium, while the Best consists essentially of zinc 10. 909834/0532 10. item) consisting of a base made of iron or an iron alloy and a coating of a Magn * »ium ~ Alumi« · nium-zinc alloy, which is about 1—4 ßew. »« § & magnesium and about 0 »05 - 5 wt .- $ aluminum contains» essential during the heat consists of zinc » 11. Object consisting of a base made of iron or an iron alloy and a coating made of a magnefium-aluminum-zinc alloy, which are about 1-4 Grew. $ Magnesium and about 5-5 Contains wt .- ^ aluminum, while the reads off essentially Zinc is made. 12. Object consisting of a base made of iron or an iron alloy and a coating made of a magnesium-aluminum-zinc alloy, which contains about 2.5% by weight & magnesium, about 4 »4% by weight of aluminum and about 93% by weight Weight ~ 9 & contains zinc. 15 »Plating bath made of a zinc alloy, approx. 1 - 4 Wt .-% contains magnesium, while the remainder consists essentially of Zinc is made. 14 · Coating bath made of a zinc alloy, which contains about 1-4% by weight of magnesium and about 0.05 "· 5% by weight of aluminum, while the remainder consists essentially of zinc. 15. Coating bath made of a zinc alloy, which contains about 2.5% by weight of magnesium, about 4 »4% by weight of aluminum and about 93% by weight of zinc. 909834/0532 bad original '