US2472402A - Zinc-copper-titanium alloys - Google Patents

Description

Patented June 7, 1949 UNITED STATES PATENT OFFICE ZINC-COPPER-TITANIUM ALLOYS No Drawing. Application June 17, 1948, Serial No. 33,670

3 Claims.

This invention relates to zinc-base alloys and, more particularly, to. zinc-base alloys containing both copper and titanium in relatively small percentages.

The United States patent to Daesen, No. 2,317,- 179, describes zinc-base alloys containing copper and one or more relatirely high melting point metals such as titanium. The patentee found that when at least 2% copper was incorporated in zinc, from about 0.02 to 0.5% of such relatively high melting point metals could also be incorporated therein to produce alloys having high creep resistance. The patentee has pointed out, however, that when less than 2% copper was used, say 1% or less, he was unable to disseminate evenly therein more than about 0.05% of the relatively high melting point metals. The patentee further pointed out that the alloys containing 1% or less of copper and not more than about 0.05% of a relatively high melting point metal did not have the resistance to cold flow or creep resistance characterized by the alloys containing 2% or more of copper together with the high melting point metal.

I have found that zinc-copper-titanium alloys containing less than 2% copper can in fact be made, by conventional zinc alloying practice, to contain as much as 0.5% or more of titanium thoroughly disseminated therein. Moreover, I have found that such alloys, within definite ranges cf proportions hereinafter set forth are of a homogeneous quality in that the titanium is thoroughly disseminated therein and are characterized by a creep resistance markedly superior to the alloys containing 2% or more of copper.

The alloys of the present invention comprise zinc-base alloys characterized by a creep resistance such that structural articles made of the alloy retain their shape under static loads normal for the use for which the article is intended. The homogeneous zinc-base alloys of the invention comprise from 0.5 to 1.5% copper, from 0.12 to 0.5% titanium, and the balance zinc. These alloys, which appear to consist of two phases, are homogeneous in the sense that the titanium is thoroughly disseminated therein in conventional alloy fashion, as distinguished from the nonuniform dissemination reported in the aboveidentified Daesen patent, and are therefore true alloys composed of the recited composition. The recited ranges of copper and titanium in the alloys of the invention represent nominal compositions which have been found to be effective. Small deviations from these limits can be tolerated while retaining a large measure of the unusual creep resistance characteristic of the alloys of the invention. For example, as little as 0.10% titanium is effective, and an amount of titanium somewhat in excess of 0.5% may be used without rendering the alloys unworkable. Although 0.5% copper appears to be the minimum for more effective properties, as little as 0.4% copper may be used within the spirit of the invention. As the copper content of the alloys of the invention approaches 1.5%, the improvement in creep resistance approaches a maximum and stars to fall ofl rapidly as the copper content increases above 1.5%. Thus, alloys containing about 1.6% copper are useful although their creep resistance is materially impaired by this increased amount of copper. The use of still greater quantities of copper so lowers the creep resistance of the alloys that at 2% copper the creep resistance of the alloys is only a small fraction of the creep resistance characteristic of the alloys of my invention.

Within the aforementioned range of composition, I have found certain narrower ranges of composition.- which are particularly useful for difierent types of articles. For example, alloys containing from 0.5 to 0.75% copper, from 0.12 to 0.25% titanium, and the balance zinc, possess excellent drawing characteristics and high resiliency in addition to high creep resistance. For example, an alloy comprising about 0.5% copper, about 0.12% titanium, and the balance high grade zinc, has been prepared and tested for resiliency and creep resistance and has been found to be particularly satisfactory for the manufacture of weather strip. At any given copper content within the range of 0.5, to 1.5%, increasing amounts of titanium up to 0.5% titanium increase the creep resistance of the resulting alloy. On the other hand, the larger amounts of titanium make the alloy more diflicult to work, although even with the maximum amount of titanium (about 0.5%) the alloys of the invention may be satisfactorily rolled and worked into rather simple shapes. For example, alloys comprising from 0.75 to 1.5% copper, from 0.3 to 0.5;% titanium, and the balance zinc, are particularly useful for structural purposes. Thus, an alloy comprising about 1% copper, about 0.4% titanium, and the balance zinc, can be rolled and corrugated without difficulty to produce corrugated roofing sheets of sufiicient creep resistance to be mounted on purlins spaced the same distance apart as that conventional for galvanized iron roofing. Thus, it will be seen that the alloys containing the smallest effective amount of titanium have the greatest workability and that this workability decreases (although creep resistance increases) with increasing titanium content. Complementing this rationale,

it appears that optimum creep resistance at any titanium content results from the use of increasing amounts of copper with increasing amounts of titanium Within the broad ranges set forth hereinabove.

In all of the alloys of the invention, the zinc base of the alloys is preferably high grade zinc. Alloys of superior creep resistance and of fine grain size when cast result from the use, as the zinc base, of metal of high purity. Zinc analyzing at least 99.99% pure is thus preferred.

On the other hand,- satisfactory alloys are obtained with zinc of the grade normally used in the production of commercial rolled zinc, for example, zinc metal containing 0.10% 0.012% iron and 0.005% cadmium. The presence of 0.1% lead is sufficient, however, to impart to the alloys (as cast) a coarse} columnar grain structure similar to that of ordinary cast zinc.

If the alloy is rolled or otherwise mechanically worked, the coarse grain structure of the cast alloy disappears. Accordingly, the microstructure and properties of the rolled or worked zinc are substantially independent of the grade or purity of the zinc base within the range of grades hereinbefore mentioned provided the alloy is subjected to mechanical working.

The alloys of the invention may be produced by reasonable extensions of conventional zinc alloy practice. For example, the requisite amounts of titanium and copper maybe added to a bath of molten zinc at a temperature of at least about 600 C. and preferably about 800 C. until both metals have been dissolved in the molten zinc. This dissolution may require many hours, possibly twelve hours or more, depending upon the amount to be dissolved and the temperature maintained. An alternative method of incorporating the titanium and copper in the zinc is to prepare first an intermediate zinc-base alloy containing a relatively high proportion of titanium and then to add this intermediate alloy to a bath of molten zinc. For example, an intermediate alloy containing about 4% of titanium may be prepared conveniently by heating a mixture of 96 parts of zinc and 4 parts of titanium in a clay-carborundum crucible at a temperature of about 800 C. for about eight hours. The resulting intermediate alloy is then cast into a thin slab and crushed to a convenient size for alloying. The final titanium content of the cast intermediate alloy usually does not depart far from the contemplated 4%. Zinc and an amount of the intermediate alloy calculated to give the desired titanium content in the final alloy are melted together and are held at a temperature of about BSD-575 C. for an hour or'so. Very little titanium is lost in this heating. Copper in amount calculated to give the desired copper content in the final alloy is added in the form of a brass intermediate after the zinc and titanium intermediate alloys are melted. The melt is then cooled to the proper casting temperature (about 500 C.) and is cast into appropriate molds.

The alloys of the invention are particularly adapted for rolling. When transformed to sheet or strip by suitable rolling procedure, the alloys possess high creep resistance. The alloys may be hot rolled at metal temperatures of from 150 to 300 C., temperatures of from 200 to 240 C. giving very satisfactory results. The hot rolling may be a finishing operation consisting of say three or more passes through the rolls, and may be applied to metal either hot or cold rolled prior to the hot finishing. Cold rolling tends to decrease the creep resistance, but the characteristic high creep resistance can be substantially restored by subsequent heat treatment such, for example, as annealing for a short period at a temperature of from 150 to 400 C., annealing in oil for about five minutes at a temperature of about 275 C. giving very satisfactory results. Cold rolling, at least in the final stages, followed by annealing for short periods of time at temperatures from 150 to 400 C., imparts to the alloy certain advantages, especially with respect to lead,

drawing. Alloys of the invention are to be considered cold rolled when the rolling (or other mechanical working) is carried out under thermal conditions resulting in a temperature of the rolled strip or sheet after the final rolling pass (final coil temperature) due simply to the mechanical working, and are to be considered hot rolledwhen the rolling is carried out under thermal' conditions resulting in a final coil tempera ture of from to 300 C., and preferably from 200 to'240 C. Maximum creep resistance of all alloys of the present invention appears to be obtained by annealing the alloy, then fa ricating, and finally reannealing.

The mechanical properties of the alloys of the invention, including their inverse creep rate, are illustrated by Table I. Mechanical properties are given in this table for five different alloy compositions A through E, each of the composi-- tions containing about the same amount of copper but varying in the amount of titanium. The rolling treatment to which each of these slabs was subjected is indicated in the column having the headingYT. The alloys were produced in 110 pound batches and three slabs having the dimensions 7" x 14 x 1 were cast from each alloy batch into conventional bottom cooled-top heated open molds. The slabs whose final coil temperatures are designated Cold under the T column were finish cold rolled with 50% reduction and had a final coil temperature brought about simply by the mechanical working. The rolling schedule for this treatment was as follows: slab heated to C., roughed on hot rolls to 0.09" in 11 passes, intermediate rolled on hotrolls to 0.036" in 3 passes, and cold finish rolled to 0.018" in 3 passes. The other specimens were finish hot rolled and the temperatures in the T column are the temperatures of the rolled strip after the final rolling pass. The rolling schedule for this treatment was as iolows: slab heated to ISO-200 C., roughed on lot rolls to 0.09" in ll passes, strip pre-heated to 150 C. and finish hotrolled to 0.018" in 3 passes with coil temperatures in the range of 210-227" C. In the table, G is the test gauge in inches; 11" is scleros'cope hardness; D. D. is dynamicductility and is measured as the max mum depth in inches of a cup that can be formed by a standard plunger in an uncut sheet of the metal without fracture; B is the cold bend value represented by the diameter of uncracked 180 bends in multiples of gauge (sheet thickness), and thus the lower values indicate better bending properties: Tem. is the per cent temper; T. S. is tensile strength in pounds per square inch; T. E. is tensile elongation, per cent in 2 inches; and C. R1 is the creep rate or creep resistance of the rolled alloy. This creep resistance is expressed in the table as the inverse creep rate. The inverse creep rate is the measured number of units of time (days) actually required to produce an elongation or creep (with the grain) of 1% in a standard test piece when subjected to a dead load indicated by the three subheadings of 12,000, 15,000 and 18,000 pounds per square inch at constant room temperature (25 C.). This inverse creep rate is therefore expressed in units of days'/%, and it will be seen that the alloys of greatest creep resistance have the highest inverse creep rate. At the bottom of Table I there also appears the" mechanical properties, including creepr'esistance, of one of these alloys (alloy A) whichha'd been cold rolled and subsequently an- 75 nealed for five minutes at 275 C.

Table I Analyzed O. 11., Days/%, ata Composition 1 o H 1). D. B Tem. T. s '1. E 000 000 Pelbcuent g p. s. l. p. s. l. p.'s.l.

Gold .018 29. 5 285 7 48 25. 800 85. 3 0044 I 0012 Cold 0185 80 280-90 5-7 45 29, 200 48. 8 017 0048 A 1.0 .12 215 .0205 25 .285 8-4 45 82,100 29.2 1.51 .074 210 .020 25 .275 8-4 40 82,400 88.2 2.05 .15 210 021 25 285 4 40 81,800 87. 5 4. 54 215 0185 280 4% 48 81, 800 82. 2 8. 77 .88 B 1.0 .84 210 .0195 25.5 .280 3% 48 82,200 35.0 4.78 .21 214 020 25. 5 280 4 5 48 32, 500 82. 8 19. 5 .88 217 0185 25 250-70 514-5 48 82, 200 27. 7 4. 95 .32 o 1.0 36 218 .0185 25 .250-70 5 49 82, 000 24.7 4.50 .17 221 0195 25 270 5-594 49 82. 000 85. 7 25. 0 25 221 0195 25 255 435-5 49 82, 700 17. 5 12. 9 29 D 1.1 .44 228 0175 25 .285-50 5-7 48 82,400 28.5 15.0 .84 227 0185 25 .250 4%5 48 88,200 28. 5 18. 1 .59 221 0195 25 .240 5-5 50 88,200 27. 5 22. 5 54 E 1.0 .47 220 0195 25.5 .240-50 45 49 85,200 80.8 88.2 .88 219 0175 25 240-50 5-7 49 88, 500 29. 2 22. 8 48 PROPERTIES 4s ANNEALED 5 MINUTES AT 275 o.

A 1.0 .12 c010 .0175 19.5 .290 4 50 27,000 44.2 1.18 .022 Cold 0180 20 290 8-4 45 25, 200 29. 7 79 018 Rolling treatments:

7 A-Finish rolled cold, 50% reduction.

B-Finish rolled hot, final coil temperature in range 210-227 C.

The effect of Working and annealing on the Table II creep resistance of a cold rolled alloy of the invention is shown in Table II. The alloy used for Inverse Creep Rate, this comparison comprised 1.0% copper, 0.12% T m Days/'73 titanium, and the balance high purity zinc. The tea 12 000 15 000 18 000 As rolled treatment comprised cold rolling to a test gauge of 0.0185 inch with a final coil temperature elevated only by the mechanical work- 28 01180 0.17 0.017 0.0048 ing of the specimen. The As drawn treatment igfiggdgg gfig 313 refers to specimens out circum-ferentially from AS annealed drawn, and 157 drawn cups. The As drawn and annealed treatment was represented by specimens cut circumferentially from drawn cups and annealed for five minutes at 275 C. The Annealed, drawn and reannealed treatment comprised annealing of the specimen for five minutes at 275 0,, followed by drawing into the form of a cup, cutting a specimen circumferentially from the drawn cup, and reannealing this specimen for five minutes at 275 C. Table II shows that a significant increase in creep resistance is obtained after annealing the cold rolled. alloy and that the combination of annealing, drawing and reannealing produces a phenomenonally high creep resistance. Additional tests have shown the alloys to be susceptible to marked improvement in creep resistance by annealingat lower Although the creep resistance of the alloys of the invention varies with the type of treatment given the alloy during fabrication, the alloys of the invention have a creep resistance superior to that of zinc-copper-titanium alloys containing at least 2% copper when the two types of alloys are given identica1 treatment. is ofiered by Table III in which there are compared the mechanical properties of six specimens Alloy F The headings in Table III are the same as those temperatures such as 150 and 200 C. in Table I.

Table II! Per Cent 0 R Specimen T G H D. D Tom. B T. S T. E. (15,000 Ti Cu p. s. 1.)

0.18 1.0 Gold .0175 .290 48 434:5 24,900 75.8 .0021 0.18 1.0 0010 .018 80 .800 47 4% 24,400 95.0 .0021 0.18 1.0 154 .018 80 .2725 45 5 28,100 71.8 .0054 0.18 1.0 189 .020 27. 5 .285 45 4:5 80,900 88.2 .088 0.18 1.0 208 .0195 25 .275 47 4% 29,800 84.8 .81 0.18 1.0 240 .019 28 .275 45 3% 29,500 1. 0.19 2.2 Gold .020 80 .220 45 7 22.000 88.7 .00057 0.19 2.2 Gold .019 20 -2175 45 7 22,800 107.0 .00085 0.19 2.2 158 .020 80 .220 48 9 25,400 70.8 .0021 0.19 2.2 158 .0185 80 .280 40 7:8 27,800 52.0 .0024 0.19 2.2 210 .0195 20.5 .255 45 5:535 28,700 49.0 .0075 0.19 2.2 248 .017 25 .250 48 5% 80,000 85.0 .088

1 Broke outside gauge length.

Such a comparison I The cold rolled specimens F-l, F-2, G-1 and (L2 were annealed in oil for five minutes at 275 C1 and then tested. The properties of the an- 'neale'd specimens are given in Table IV.

Itwill be seen from Tables III and IV that the alloys of the" present invention have creep resistance consistently superior to th'at'of the known alloys containing at least 2% copper when" finished under substantially similar conditions. which may ormay not be the optimum treatments for either type of alloy. The same superior creep resistance of the alloy of the invention is dislayed by the cold rolled specimens after annee-ling in oil for five minutes at 275 C. In comparing the creep resistance of diiierent alloys it must be borne in mind that a difierence in the static load makes a tremendous difierence in the measured creep rate. The inverse creep rate tends to decrease approximately at a logarithmic rate as the static load is increased, as can be seen clearly in Tables I and II. Inverse creep rates under static loads as low as 10,000 pounds per'square-inch' are so high withthealloys of the present invention that their measurement would generally require days or even years. Thus, in order to accelerate the tests, static loads of at least 12,000 pounds per square inch have been used in preparing the data reported herein.

The high creep resistance of the alloys of the invention makes possible their successful use in application's where zinc and zinc' alloys have heretofore been unsatisfactory. For many such applications there is no arbitrary minimum creepresistance which determines whether or not an alloy'is suitable. In such cases, the suitability of the" alloy can only be ascertained by making the desired article with the alloy in question and testing it under normal conditions of use; In a few such instances as sheet roofing material, a reasonable indication of the suitability of an alloy maybe obtained by a simulated test. For example, a corrugated sheet of an alloy may be supported on purlin's spaced at the desired space with additional sheets lapped over the edges and ends of the test sheet to approximate the mutual support of adjacent sheets on a roof. When such a sheet is supported on purlins' having a conventional span of 5% feet and is subject to a uniform load of pounds per square foot, this being the estimated maximum roof' stress due to snow and wind in northeastern United States, the criterion of success is that the sheet should not sag more: than 0.75% of the. span in 30 days during cool weather. An alloy of the present invention, comprising 1% copper, 0.4% titanium, and the balance zinc, when? hot rolled to 0.032" gauge and annealed both before and after corrugating (the corrugation being 2%" from crest to crest and. 1" deep), is the only zinc-base alloy which I have ever found to pass this test in such fabricated form.

This application is a continuation-in-part of my copending application Serial No. 533,791, filed May 2, 1944, now abandoned.

I claim:

1 A homogeneous zinc-base alloy comprising from 0.5 to 1.5% copper, from 0.12 to 0.5% titanium, and the balance zinc, said alloy having a creep rate such that when the alloy is finish cold rolled to 0.018 inch strip with reduction the'resulting'strip requires at least 0.0044 day for 1% elongation when subjected to a dead load tension of 15,000 pounds per square inch.

2. A homogeneous zinc-base alloy comprising from 0.5 to 0.75% copper, from 0.12 to 0.25% titanium, and the balance zinc, said alloy having a creep rate such that when the alloy is finish cold rolled to 0.018 inch strip with 50% reduction the: resulting. strip requires at least 0.0044 day for 1% elongation when subjected to a dead load tension of 15,000 pounds per" square inch.

3. A homogeneous zinc-base alloy comprising from 0.75 to 1.5% copper, from. 0.3 to 0.5% titanium, and the balance zinc, said alloy having a creep rate such that when the alloy is finish cold rolled to- 0.018 inch strip with 50% reduction the resulting strip requires at least 0.0044

day for 1% elongation when subjected to a dead load tension of 15,000 pounds per square inch.

EDWARD J. BOYLE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Metals Handbook, 1939 edition, pages 1737, 1765' published by American Society for Metals, Clevelan'd, Ohio.