US3388987A

US3388987A - Cathodic protection alloys

Info

Publication number: US3388987A
Application number: US495321A
Authority: US
Inventors: Bailey Ronald Ernest
Original assignee: British Aluminum Co Ltd
Current assignee: British Aluminum Co Ltd
Priority date: 1964-10-21
Filing date: 1965-10-12
Publication date: 1968-06-18
Anticipated expiration: 1985-06-18
Also published as: GB1118302A

Description

United States Patent 3,388,987 CATHODIC PROTECTION ALLOYS Ronald Ernest Bailey, Ickenham, Uxbridge, England, as-

signor to The British Aluminium Company Limited, London, England, a company of Great Britain N0 Drawing. Filed Oct. 12, 1965, Ser. No. 495,321 Claims priority, application Great Britain, Oct. 21, 1964, 42,969/ 64 4 Claims. (Cl. 75146) This invention relates to improvements in cathodic protection alloys.

Various aluminum-base alloys have previously been proposed for use as sacrificial anodes for the cathodic protection of metal structures against corrosion by contact with sea water and related electrolytes such as estuarine waters. One such alloy includes tin 0.01 to 2%, zinc 0.5 to copper 0 to 0.015%, magnesium O to 0.05%, silicon 0 to 0.25%, iron 0 to 0.35%, titanium 0 to 0.01% and manganese 0 to 0.1%, the tin being dispersed throughout the alloy matrix, the balance being aluminum and inconsequential impurities. The aluminum used in the manufacture of such an alloy would generally be 99.8% commercial purity aluminum and gallium would normally be present as an inconsequential impurity in the proportion of not more than 0.02%, being derived from the bauxite from which the aluminum is produced. The tin would generally be dispersed throughout the alloy matrix by a suitable form of heat treatment, thi being desirable in order to avoid uneven attack and hence low efficiency and to avoid undesirable variation in potential of the alloy when used as a sacrificial anode.

It is to be understood that the percentages referred to in this specification are all by Weight.

In the prior proposal referred to above, the preferred upper limit for titanium is set out as being 0.005%. We have found that, contrary to expectation, the upper limit of 0.01% for titanium may be exceeded without deleterious effect, and, indeed, certain advantages result from such increased titanium content. Thus, the appearance of the casting is improved Wherecast anodes are used, a more uniform structure of the alloy results which is beneficial to both cast and extruded anodes, and there is also achieved a better contact with and minimising of voids at the steel core of anodes cast from the alloy.

According to the present invention, there is provided for use as a sacrificial anode material an aluminum base alloy including 0.5 to 10% zinc, 0.01 to 2% tin, 0 to 0.015% copper, 0 to 0.05% magnesium, 0 to 0.25% silicon, 0 to 0.35% iron, 0 to 0.1% manganese and titanium in excess of 0.01% but not more than 0.1%, the tin being dispersed throughout the alloy matrix and the balance being aluminum and inconsequential impurities.

3,388,987 Patented June 18, 1968 ice Preferably, the titanium content of the alloy is in the range of from 0.02 to 0.06%.

An aluminum-base alloy material according to the present invention which has been found to be particularly useful has the following composition::

Percent Zinc 5.5 Tin 0.10 Iron 0.10 Silicon 0.10

0.04 Copper 0.005 Manganese 0.005 Magnesium 0.005

Balance aluminum and inconsequential impurities. The aluminum used was 99.8% commercial purity. The tin was dispersed throughout the alloy matrix by a suitable heat treatment which involved heating the alloy for 8 hours at 470 C. and quenching in water and with no artificial ageing.

The alloy had an efiiciency of 785% as measured by an impressed current technique and a potential measured on the saturated Calomel scale of -1.100 v. The efficiency is defined for present purposes as the ratio of the metal dissolved in producing current to the total Weight of metal dissolved.

I claim:

1. An aluminum base alloy for use as a sacrificial anode material consisting essentially of 0.5 to 10% zinc, 0.01 to 2% tin, up to 0.015% copper, up to 0.05% magnesium, up to 0.25% silicon, up to 0.35% iron, up to 0.1% manganese and titanium in excess of 0.01% but not more than 0.1%, the tin being dispersed throughout the alloy matrix and the balance being aluminum and inconsequential impurities.

2. An alloy according to claim 1 wherein the titanium content is in the range of from 0.02 to 0.06%.

3. An aluminum base alloy for use as a sacrificial anode consisting essentially of 5.5% zinc, 0.10% tin, 0.10% iron, 0.10% silicon, 0.04% titanium, 0.005% copper, 0.005% manganese, 0.005% magnesium, the tin being dispersed throughout the alloy matrix, and the balance being aluminum and inconsequential impurities.

4. An alloy according to claim 1 in which the aluminum is 99.8% commercial purity aluminum.

References Cited UNITED STATES PATENTS 3,321,305 5/1967 Hine -146 HYLAND BIZOT, Primary Examiner.

RICHARD O. DEAN, Examiner.

Claims

1. AN ALUMINUM BASE ALLOY FOR USE AS A SACRIFICIAL ANODE MATERIAL CONSISTING ESSENTIALLY OF 0.5 TO 10% ZINC, 0.01 TO 2% TIN, UP TO 0.015% COPPER, UP TO 0.05% MAGNESIUM, UP TO 0.25% SILICON, UP 0.35% IRON, UP TO 0.1% MAGANESE AND TITANIUM IN EXCESS OF 0.01% BUT NOT MORE THAN 0.1%, THE TIN BEING DISPERSED THROUGHOUT THE ALLOY MATRIX AND THE BALANCE BEING ALUMINUM AND INCONSEQUENTIAL IMPURITIES.