US3680626A

US3680626A - Corrosion-resistant surface coating for use in the casting of aluminum and aluminum alloys

Info

Publication number: US3680626A
Application number: US876369A
Authority: US
Inventors: Kaneyoshi Kusunoki; Tatsumi Asakura; Masahiro Nakakawa; Noboru Komatsu; Tohru Arai
Original assignee: Toyota Motor Corp; Toyota Central R&D Labs Inc
Current assignee: Toyota Motor Corp; Toyota Central R&D Labs Inc
Priority date: 1969-04-15
Filing date: 1969-11-13
Publication date: 1972-08-01
Anticipated expiration: 1989-08-01
Also published as: FR2030720A5; GB1292625A; JPS4828537B1; DE2010323A1

Abstract

To prevent the corrosion of the surfaces contacting molten aluminum and aluminum alloy when such molten materials are being cast, a surface layer of boron impregnated ferrous materials is provided on the contacting surfaces of the containers and other conveying members used in the casting of the molten aluminum and its alloys.

Description

United States Patent Kusunoki et al.

[451 Aug. 1, 1972 1541 CORROSION-RESISTANT SURFACE COATING FOR USE IN THE CASTING OF ALUMINUM AND ALUMINUM ALLOYS Inventors: Kaneyoshi Kmunoki; Tatsuml Assignees:

Filed:

Appl. No.:

Asakura;Masah1roNakakawa,allof Toyota-shi; Noboru Komatsu; Tohru Aral, both of Nagoya-shi, all of Japan Toyota .Ildosha Kogyo Kabushiki Kaisha, Toyota-shi, Aichi-ken; Kabmhiki Kaisha Toyota Chuo Kenltyusho, Nagoya-shi, Aichi-ken, Japan Nov. 13, 1969 Foreign Application Priority pm April 15, 1969 Japan ..44/28689 US. Cl

Int. Cl.

....... ..l64/l38, 117/DIG. 10, 164/72,

...................... ..B22c l/00, B22c 3/00 Field of Search ..l48/3l.5; 164/72, 138;

1l7/D1G. 10, 5.3; l06/38.9; 249/116 REDUCTION IN THlCKNESSlmm) Primary Examiner-J.

Spencer Overholser Assistant Examiner-V. K. Rising Attorney-McGlew and Toren ABSTRACT To prevent the corrosion of the surfaces contacting molten aluminum and aluminum alloy when such molten materials are being cast, a surface layer of boron impregnated ferrous materials is provided on the contacting surfaces of the containers and other conveying members used in the casting of the molten aluminum and its alloys.

llClaimZDrawingflgures ORON IMPREGNATED DURATION OF IMMERSION (nouns) m uou'eu ALUMINUM ALLOYS PATENIEU 1'97? 3,680,626

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UNTREATED BORON IMPREGNATED l l l l DURATION OF IMMERSION (HOURS) IN MOLTEN ALUMINUM ALLOYS REDUCTION IN THICKNESS(mm) INVENTOR mmiyosm xusuuom 'rnrsum nsnkuan, nnsn'mo lnnnnnn;

, "301w KOHRTSu TON'RU HRnl BY 5 M ATTORNEY CORROSION-RESISTANT SURFACE COATING FOR USE IN THE CASTING OF ALUMINUM AND ALUMINUM ALLOYS SUMMARY OF THE INVENTION The present invention is directed to the prevention of corrosion in the contacting surfaces of containers and other members employed in casting and forming ingots of aluminum and aluminum alloys and also to the prevention of the mixing of impurities into the aluminum and its alloys during the casting operation. Moreover, the invention is directed to a boron impregnated ferrous material surface coating on the members in contact with the aluminum and its alloys during the casting operation.

Generally, pure aluminum is likely to combine with other elements and as a result to form various compounds. Similarly, aluminum alloys which may contain quantities of copper, silicon, magnesia, nickel, manganese, and the like, for the purpose of obtaining mechanical strength or for achieving other properties suitable for casting or working, does not exhibit the desired properties if impurities are mixed with the alloy elements. Moreover, the materials used in forming the containers and other members for casting pure aluminum and aluminum alloys and for forming ingots of the cast material must be such so as to prevent the mixing of impurities into the molten aluminum and its alloys and also to prevent corrosion of the surfaces of the vessels and other members contacting the molten metal.

To prevent corrosion and the mixing of impurities into the molten metal, materials having stable properties at high temperatures, for instance, refractory oxides such as kaolin, quartz, magnesia, lime and others, or carbonaceous materials such as graphite, are commonly used to line the containers and other members employed in the casting and molding operations. However, such surface linings are difficult to form and are easily damaged and displaced. Moreover, in the interest of improving the productivity and the strength of the cast products, continuous casting, low pressure casting and die casting operations have been used. In such operations, other conveying members of complicated shapes are immersed in the molten metal and molten metal is moved to other locations through transfer members or tubes. It is difficult and impractical to effect the surface coating on such other members or tubes employing the prior art surface coatings mentioned above.

Therefore, it is the primary object of the in vention to provide a corrosion-resistant surface layer for the containers and other members used in the casting of aluminum and aluminum alloys and in molding'the aluminum and its alloys into ingots and the like, Further, it is the intention of the present invention to provide a surface coating which is easily applied even to the contacting surfaces of containers or other members of complicated shapes or to the interior surfaces of tubular members. By employing the surface coating of the present invention, the inclusion of impurities into the aluminum and aluminum alloys being cast can be prevented and the life of the containers and other members being used can be prolonged.

Therefore, in accordance with the present invention, at least the contacting surfaces of containers and other members employed in the casting and molding ofaluminum and aluminum alloys is provided with a boron impregnated ferrous material layer. In addition, the present invention encompasses the application of boron impregnated layers on the surfaces of containers and other members used in casting and molding aluminum and aluminum alloys, which are formed of carbon steel, cast iron, cast steel, and. special purpose steels such as stainless steel.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a diagram illustrating the corrosion-resistant characteristics of two samples of a stainless steel, one with and one without a boron impregnated surface layer, immersed in molten aluminum alloy; and

FIG. 2 is a sectional view of a container used in casting aluminum having a surface coating in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 2, one example ofa container 10 is shown which is used in the casting and molding of aluminum and aluminum alloys. A surface layer 2 composed of boron-impregnated ferrous materials is formed on the surface of the container which contacts the molten aluminum and aluminum alloy.

It is well known to impregnate boron into structural steel and tool steels for obtaining increased hardness characteristics on the surfaces of wear-resisting articles and for machine tools. Various impregnating processes have been used including gas, solid, and liquid methods, and in certain instances the liquid methods may include an electrolytic operation. In the casting and molding operation, variouscontainers and members are used, such as smelting crucibles, ladles, gutters, pipes, molds and the like. Such containers and members are made from ferrous materials, such as chrominum stainless steel and 18-8 stainless steel, and, in accordance with the present invention, the entire extent of such containers or members or at least the surfaces which come in contact with the molten aluminum and its alloys are impregnated with boron.

- As exemplary of the advantages obtained in corrosion-resistance by virtue of the present invention, the

following examples are provided in which stainless steel samples were tested, certain of which were provided. with a boron impregnated surface coating.

EXAMPLE I ing of 90 percent by weight of borax and percent by weight of zirconium oxide maintained at 950C, and at the same time it was electrolyzed for 2 hours at a current'density of 0.5 A/crn' with the test sample acting as the cathode. In this procedure a boron impregnated layer of about 40 microns in depth was formed on the surface of the sample. The test samples, one with and one without the boron impregnated surface coating, were immersed into a molten JIS AC4B aluminum alloy of about 2kg maintained at 700C. The depth of the corrosion on the test pieces was measured and is set forth in FIG. 1. The test sample coated with the boron impregnatedlayer corroded only 0.1mm in depth after a period of 30 hours,however, the untreated test sample corroded to a depth of 0.8mm in about 5 hours and the corrosion reached a depth of 1.7mm after 30 hours.

EXAMPLE n In this example, a test sample of stainless steel having the same dimensions and similarly impregnated with boron as in Example I, and an untreated test sample of HS FC cast iron having the dimensions of 20 mm in diameter and 30mm in length were immersed into about 3kg of molten aluminum maintained at 750C. From past experience it has been determined that of the various ferrous metals, cast iron has the highest resistance to corrosion in molten aluminum. However, the results obtained in this test indicated that the sample of cast iron had corroded to a depth of about 2mm after 20 hours immersion, while the boron impregnated sample of stainless steel had corroded only to a depth of 0.1mm. Since the time period in which the molten aluminum or its alloy are in contact with the surfaces of the containers or members in the casting or molding operation is much less than the time periods involved in the test examples, the amount of impurities mixed into the ingots or cast products can be ignored. The useful life time of the containers and other members having the surface layer of boron impregnated ferrous materials is prolonged and any inclusion of impurities into the aluminum or aluminum alloys will be decreased.-

In view of the various methods available forefl'ecting boron impregnation, such as gas, liquid and solid methods, themost effective and efficient method of impr'egnation can be selected based on the shape of the articles to be coated. Further, mixing of boron into aluminum and aluminum alloys is preferable since it tends to improve the quality of the castings because the addition of boron to aluminum and its alloys serves to refine the metallurgical structure.

We claim:

1. Method of corrosion and preventing the absorption of impurities in the, manufacture of aluminum castings subject to corrosion and absorption of impurities therein, which comprises:

a. heating the aluminum eating material and bringing the aluminum material to a molten state,

b. preparing a ferrous receptacle for receiving the molten aluminum casting material by coating the innersurfaceofsaidreceptaclewithathinlayerof boron metal,

c. placing the molten aluminum casting material into the ferrous receptacle whose inner surface has n coa 'th boron metal, and owing uminum casting to cool, separating and recovering the cooled aluminum casting from the receptacle.

2. Method according to claim 1, wherein said receptacle is a mold.

3. Method according to claim 1, wherein said receptacle is selected from stainless steel, chromium stainless steel, and cast iron.

4. Method according to claim l, whereinthe boron metal'is coated on said receptacle to about 40 microns in depth.

5. Method according to claim 1, wherein the boron metal is coated on said receptacle at a temperature of about 950C.

' 6. Method according to claim 1, wherein said receptacle consists of stainless steel.

7. Method according to claim 1, wherein said receptacle consists of cast iron.

8. Method according to claim 1, wherein said coating of boron metal is effected by electrolysis.

9. Method according to claim 8, wherein said electrolysis is carried out in a molten salt bath comprising an alkali metal borate.

10. Method according to claim 9, wherein said metal borate is sodium borate.

11. Method according to claim 10, wherein the receptacle is prepared by dipping in a molten salt bath consisting of (i) about percent by weight of borax and (ii) about 10 percent by weight of zirconium oxide, maintaining the bath at a temperature of about 950C., electrolyzing the bath for about two hours at a current density of about 0.5 A/cm', the receptacle being the cathode.

Claims

2. Method according to claim 1, wherein said receptacle is a mold.
3. Method according to claim 1, wherein said receptacle is selected from stainless steel, chromium stainless steel, and cast iron.
4. Method according to claim 1, wherein the boron metal is coated on said receptacle to about 40 microns in depth.
5. Method according to claim 1, wherein the boron metal is coated on said receptacle at a temperature of about 950* C.
6. Method according to claim 1, wherein said receptacle consists of stainless steel.
7. Method according to claim 1, wherein said receptacle consists of cast iron.
8. Method according to claim 1, wherein said coating of boron metal is effected by electrolysis.
9. Method according to claim 8, wherein said electrolysis is carried out in A molten salt bath comprising an alkali metal borate.
10. Method according to claim 9, wherein said metal borate is sodium borate.
11. Method according to claim 10, wherein the receptacle is prepared by dipping in a molten salt bath consisting of (i) about 90 percent by weight of borax and (ii) about 10 percent by weight of zirconium oxide, maintaining the bath at a temperature of about 950* C., electrolyzing the bath for about two hours at a current density of about 0.5 A/cm2, the receptacle being the cathode.