US2023512A - Duplex metal article - Google Patents

Description

DUPLEX METAL ARTICLE Filed 001;. 20. 1933 INVENTOR R obs/ff). Bro wn BY Patented Dec. 10, 1935 'UNITED- STATES PATENT OFFICE" DUPLEX METAL ARTICLE Robert H. Brown, New Kensington, Pa., assignor to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania Application October 20, 1933, Serial No. 694,445

Claims. (01. 29-181) This invention relates to duplex metal articles, and it is particularly concerned with the production of an improved duplex metal comprising a base of aluminous metal (aluminum or aluminum 5 alloy) provided on one or more of its surfaces with an aluminous metal coating resistant to deep pitting by corrosion.

It has heretofore been proposed to produce aluminous duplex metals, particularly of the type comprising a core of strong aluminum alloy provided with a coating consisting of pure aluminum or an aluminum alloy more resistant to corrosive attack than the core metal. The coating in these duplex metals is formed of a, single layer of metal of substantial thickness which constitutes an appreciable part. of the total thickness of the duplex metal. Upon exposure of such material to corrosive conditions, a local action takes place which may cause relatively rapid penetration through the coating to the base metal, forming pits which are relatively deep and of small circumference. The surface appearance of the duplex metal is materially impaired by this type of corrosion and the protection afforded the base metal is often .25 partially destroyed.

It is an object of the present invention to overcome the difiiculty of pitting in duplex metal surfaces and to provide an improved duplex metal article in which corrosive attack is distributed 30 over a relatively wide surface area before penetrating to a substantial depth. A further object of my invention is to provide an improved duplex metal article having an aluminous metal base provided with an aluminous metal coating sub- 35 stantially resistant to pitting which retains a relatively smooth, even surface appearance under corrosive conditions. More particularly, it is an object of my invention to provide an improved duplex metal article consisting of ari aluminous 40 metal base provided with a coating composed of a plurality of aluminous metal layers or laminations. 1

I have discovered that if an aluminous metal base be provided with a laminated coating con- 45 sisting of two or more layers of aluminous'metal in which each layer possesses an electrode potential greater than that of the base metal and in which. the successive layers of the laminated coating are so arranged that the electrode po-' 50 tential of the coating increases progressively from which penertatethrough the coating to the base metal, the corrosive attack'spreads laterally after penetrating the first layer of the laminated coating and does not penetrate the second or successive layers of thecoating material until the layer 5 first penetrated is extensively corroded in a lateral direction. This effect is the direct result of the selection and arrangement of the materials of the successive layers of my improved duplex metal article with regard to the electrode poten- 10 tial of the aluminous metal employed in each layer. The electrode potential of the surface or other layer being always greater than that of the layer next below it, at any point where any two of these layers are exposed in contact with a 15 corroding medium, the voltaic action set up causes a: preferential attack of the metal of higher electrode potential, thus protecting the layer of lower electrode potential. v

In forming the duplex metal articles of my in- 20 vention the proper choice and arrangement of the aluminous metals to be used'in combination depends upon a predetermined knowledge of the electrode potential of the various aluminous metals. These difierent potentials are readily measured, in accordance with the methods long known in the art, against a standard electrode. If the electrode potentials of the layers of the aluminous metal coating are electronegative with respect to the standard electrode, it is not neces-. sary that the base metal be electropositive withrespect to the'standard electrode, but only that the base metal be less electronegative than the coating metal, and that the layers of the coating be successively, more electronegative than the base metal. Therefore, throughout this speciflcation and claims, when I say that the electrode potential of the various layers of the coating should be higher than that of the base metal, I

mean that the aluminous metals of the various 40 layers of the coating should be more electronegative with respect to the standard electrode than is the base metal. While no fixed potential difference is required between the electrode potential of the aluminous metal base and the coating, or between any two adjacent layers of the coating, it is desirable that there be a relatively wide difference in the electrode potential of any two adjacent layers, since I have found that with greater difierence in electrode potential corrosive attack proceeds laterally to a greater extent and spreads the corrosion over a wider surface area, thus producing a material with greater resistance to penetration by pitting. A convenient standard electrode for measuring may be readily produced. In general, the followthe potentials above mentioned may be readily structural, properties, may be any aluminum .alselected from those now in regular use for simloy having the properties which it is'desired to ilar measurements. For the-purposes of this deobtain inthe finished article. scription'of the invention a. calomel electrode it is desired that the article, have high strength has been selected as a standard. In measuring and hardness, an alloy 0. the duralumin type alloy to be tested is made one element of an elec- 0 below mentioned; or if it is desired to obtain trolytic cell. The calomel electrode is made the an article which combines the properties of exother element. The electrolyte a normal solution of sodium chloride containing 0.3 per cent by D, E, or F below mentioned maybe used. Also, weight .of hydrogen peroxide. The circuit is other alloys possessing known combinations of closed and the potential dificerence of the eleproperties may be employed, such as any of the ments is measured on a potentiometer. The calfollowing: omel electrode used is made up in the usual way w f mercury 11! Contact W h 11181121110115 011101111 Alloy Composition-Percentage byweight-Bslancealuminum and in contact with this a normal potassium chloride solution saturated with mercurous chlo- Mapper,1258mmojmanganesemsmagnesmm A ride 3 efipper, silicon,. 0.75 manganese, 0.5 magnesium.

8 con, magnesium. The aluimnous metals to be used in forming Commercial aluminum the laminations of the composite coating metal E 1.25 manganese. may be aluminum or substantially any of its 5;; mganesell-omagnesmm- 0.7 s ilicon, 1.25 magnesium, 0.25 chromium.

5 silicon.

4.0 copper, 0.5 magnesium, 2.0 nickel.

4.5 copper, 0.8 silicon, 0.8 manganese.

0.8 copper, 0.8 nickel, 12.5 silicon, 1.2 magnesium.

alloys of suitable electrode potential. For the purpose of forming'laminations of suitably graded electrode potentials I have found it particularly convenient to use alloys of aluminum and one or ffi figf more of the metals silver, tin,indium,bismuth, cal- N.- 10 silicon. I

0.- 4.5 copper, 5.0 silicon.

cium, barium, strontium, cadmium, zinc, platinum, and gallium in varying amounts. As is described Q-- in my copending U. S. Patent application, Serial No. 694,444, filed October 20, 1933, these metals have the property of increasing the electrode potential of aluminous metals without otherwise modifying their desirable properties, when added thereto in relatively small amounts. Consequently, by the addition of progressively increasing amounts of these metals to successive layers of the composite coating metal a coating material having the desired electrode potential properties l4 silicon, 2.0 nickel, 1.0 magnesium.

6.0 copper, 1.0 tin.

7.0 copper, 7.0 nickel, 7.0 silicon.

. 6.0 magnesium, 1.5 nickel, 1.0 manganese.

In some cases the composite coating metal prepared as above described may possess sufiicient ed application. In such case a composite laminated structure may be produced in which there is no single layer from which the structure derives its physical properties. In fact, it has been found that for certain applications a coating metal prepared as above described is useful without application to a base. It is to be understood, therefore, that the duplex metal articles of my invention contemplate articles which derive their strucing amounts of metals of the class'above de scribed best serve the general purpose of this invention in producing the electrode potential desired without materially impairing other detural properties from the properties of the alushfable properties of the aluminuma'noys' minous metals forming each of the layers, as well Percent"'---. as such duplex'metal articles as derive their structural properties for the purpose of its intend- If, for examp'e,

6 v the electrode potential in question, the aluminum may be used as the base, such as alloys A, B, or

treme ductility with workability, alloys of the type sflver Q02 to principal structural properties from a single base Cadmium 0.05 to 5.0 layerv m gnu (mg to In forming the duplex metal articles of my in- Caloium (L1 to L0 vention, in which a relatively thin laminated coat- Barmm {M to 2 ing is applied to a metal base having desired strucs m to L0 .tural properties, any of the known methods of Gallium 0.02 to 2.0 forming such duplex metal articles may be used. Indium 0.02 to 29 One method which I have found particularly Bismuth mg to L0 satisfactory is to cast the base alloy against the Tin (m2 to 05 I formed laminated coating metal, as described in zinc 02 to 101) the patent of E. H. Dix, No. 1,865,089, issued June 28, 1932.. The article may then, if desired, be mechanically worked, as for example by rolling or drawing or other suitable operation, to form the particular type of duplex metal article desired, such as sheet, rod, or other form of material. The working with intermediate heating incident by the use of a greater number of laminat1ons A to such forming operations tends to improve the suitable method of forming such a material is bond between th1aminafins coating and to first form a pack of superimposed sheets of between the coatmg the base metalthe various aluminous metals which are to con- The duplex metal articles of my invention may stitute the individual laminations, and then by a b Provided on any Or all of their exlwsed rolling operation reduce the thickness of the pack surfaces with Protective mposite coating to the desired thickness. This reduction produces m For example there is Shown in the drawextremely thin laminations in the finished coating a duplex metal article wmprising base of ing metaL I an aluminum structural alloy provided on its The base or core metaL-that is to say the layer p and bottom S ac with a laminated Coator body of metal irom which the duplex metal ing metal 2 and The ba e I may e d.

The composite coating metal may be formed of any desired number of laminations of any desired thickness. In' general, however, the surface appearance is better retained if the individual laminations are extremely thin and the desired thickness of the coating metal is built up articles of my invention derives its principal for example, of an alloy consisting of aluminum The layer 3 may consist of an alloy of aluminum and 0.05 per cent tin, the layer 6 being formed of analloy of aluminum, 0.05 per cent tin, and 0.05

per cent bismuth. I

I claim as my invention:

1. A duplex metal article consisting of a base of aluminous metal provided with a coating consisting of a plurality of aluminous metal layers, each of said layers having an electrode potential greater than that of the base metal and having said layers arranged in the order of increasi electrode potential from the base metal to the surface of said article.

2. A duplex metal article consisting of a base of aluminous metal provided with a laminated aluminous metal coating composed of a plurality of aluminous metal layers, each of said layers having a diilerent electrode potential and all of said layers having electrode potentials greater than that of the base metal, said laminated coating having an electrode potential which increases progressively through successive layers from the base metal to the outer surface of said article.

3. A duplex, metal article consisting of a base of aluminous metal provided with a laminated aluminous metal coating having an electrode potential which increases throughout its thickness iii-om the base metal to the outer surface of said article, said coating being resistant to pene= tration by corrosion.

4. A duplex metal article consisting of a base of aluminous metal provided with a laminated aluminous metal coating having an electrode po- 5 tential which increases throughout its thickness from the base metal to the outer surface of said article and being resistant to penetration by corrosion, said coating being composed of a plurality of extremely thin aluminous metal layers, each 10 of said layers consisting predominantly of aluminum and at least one of the class of metals silver, cadmium, zinc, platinum, calcium, barium, strontium, gallium, indium, bismuth and tin, each of said layers having an electrode potential greater than that of the base metal.

5. A duplex metal article consisting of a base of aluminous metal provided with a lated aluminous metal coating having an electrode potential which increases throughout its thickness from the base metal to the outer surface of said article and being resistant to penetration by corrosion said coating being composed of a plurality of extremely thin aluminous metal layers, each of said layers consisting predominantly of aluminum and at least one of the classof metals silver,

cadmium, zinc, platinum, calcium, barium, strontium, gallium, indium, bismuth and tin, each of said layers having an electrode potential greater than that of the base metal and greater than that of substantially pure aluminum.

. ROBERT H. BROWN.

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