US2412045A - Zinc base alloy containing copper and beryllium and process for heat-treating the same - Google Patents

Description

Patented Dec. 3, 1946 zrNo Bass ALLOY CONTAINING COPPER AND .BERYLLIUM AND PROCESS on HEAT-TREATING THE SAME V Richards H. Harrington, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York No Drawing. Application June 28, 1943,

Serial No. 492,588

The present invention relates to zinc base alloys containing copper and beryllium and more particularly to precipitation hardened alloys of that composition.

Commercial zinc hardens only slightly by cold rolling since it tends to recrystallize rapidly at room temperature. Since zinc possesses an hexagonal lattice, its lattice orientation tends to line up with the direction of rolling. This results in a diflerent set of tensile properties for the direction of rolling as compared with the direction transverse to rolling. The transverse tensile strength is thus usually about higher than for the with-rolling direction. For purposes of comparison herein only the properties developed in the direction of rolling will be considered. Thus zinc containing 0.05% Pb,.0.0l Fe, 0.005 Cd, when cold rolled develops a tensile strength of 16,000 per square inch and an elongation of about to Certain commercial alloys of zinc have somewhat improved properties after cold rolling and recrystallize at slightly elevated temperatures in the range of -105 C. However these recrystallization temperatures are still too low to allow such zinc alloys to be compared with cold rolled brasses or aluminum alloys on any equivalent basis. For example, a typical commercial zinc base alloy, consisting of 1% Pb, 0.02 Fe, 0.35 Cd,

0.65-1.25 Cu, 0.025 Mg, when cold rolled, develops stress-strain curves from tensile tests generally show no ranges where the stress is proportional to strain and the alloys have essentially no practical elastic properties for uses such as springs. Moreover, these materials are characterized by such high rates of flow at low loads that, although a standard alloy may have a tensile strength of 35,000 per square inch, engineering usage is based on an empirical maximum stress of 10,000 per square inch.

It is one of the objects of the present invention to provide a zinc base alloy containing copper and beryllium and having high physical properties. It is a further object to provide a zinc base alloy which retains its work-hardened properties at higher temperatures.

taining copper and beryllium which hasv physical properties comparable with wroughtaluminum alloys and brasses having comparable elongation and ductility. A further object of the invention A further object' of the invention is the provision of a zinc basev alloy con- 18 Claims. (Cl. 148-115) is to provide a zinc base alloy containing copper and beryllium which is suitable for uses such as lamp and fuse bases, sockets, springs and electrical conductors as well as certain types of cartridges, shells etc. Other objects will appear hereinafter.

In carrying out the present invention I employ a zinc base alloy which contains from about .6 to about 3% copper, and from about 0.03% to about 0.35% beryllium, the remainder being substantially all zinc. Zinc will dissolvea maximum of 2.7% copper in'solid solution and to :be heat treatable the copper content of the alloy in-general should be in excess of 1%; Alloys of zinc and beryllium are very difiicult, if not impossible, to make by ordinary alloying processes. Berylwhile zinc melts at 419 C. and boils at 907 C. Solid' beryllium does not readily diffuse into molten zinc but copper on the other hand does dissolve readily in molten zinc. When copperberyllium master alloys normally containing about 3 to 12% beryllium are added in small quantitles to molten zinc the copper atoms dissolve rather rapidly in the melt and the beryllium atoms, perforce, must go along. Thus various ratios of copper to beryllium are made possible and the alloys are readily made by ordinary melting procedures. The presence of copper in excess of 2.7% and beryllium in excess of 0.3% re: sults in excess phases which are incapable oisolubility of heat treatment for subsequent precipitation, decreased ductility for fabrication and increased cost. The analysis of the zinc base alloy which I prefer contains 1.9 to 2.1% copper, and 0.05 to 0.15% beryllium. A zinc base alloy containing 1.25% copper and 0.07% beryllium yields slightly lower useful properties and a lower recrystallization temperature of 150 Qalthough these properties are still in excess of those for present commercial alloys.

Although I prefer to emplo an alloy consisting of zinc, copper and beryllium, the machinability of the alloy as well as its ductility in cold forming may be improvide without adverse effect on the. physical properties of the alloy by the presence of small quantities of one or more additional elements, for example 0.2 to 1.5% lead, 02 to 1% manganese and 0.2 to-1% aluminum. U

. In preparing the alloys the composltions na'y be formed by one or the other of the two-procedures; la) by direct-addition of the desired-copper-beryllium master alloy containing about-2 to 12 beryllium to molten zinc, or (b) byforming asecondary master alloy of 70% zinc and 30% lium melts at 1280 C. and oxidizes rapidly in air beryllium master alloy containing 2 t 121 31 beryllium is placed on the bottom ofa crucible and covered with 70% by weight of high purity zinc. As the zinc melts it will wet and coat the copper-beryllium master alloy andthus reduce to a minimum any losses due to oxidation. After the zinc is melted the temperature is increased and held in a range reasonably below the boiling point of zinc; for example a range varying from about 750 to 850 C. Within two to four hours the formation of the secondary master alloy containing about:70% zinc and 30% copper-beryllium, will be complete and it may be poured preferably into iron mold pigs of any convenient size although graphite or sandmolds may be employed if desired.

To obtain a desired alloy composition the proper pure zinc charge is melted and the tem-, perature raised to about 450 to 650 C. "The re quired amount of secondary master alloy, that is 70% zinc plus 30% copper-beryllium is then added and quickly alloyed with the zinc. 'The final alloy is then cast into the desired ingot or casting shape in sand, preheated graphite, or metal molds. Castings made in the metal ,molds will have a finer grain size and slightly better properties as cast but will not be essentially different after heat treatment and cold Working from the alloys which are cast in other forms BN0. 1. 2.11 Cu0.09 'Bebalance Zn No. '2. 1.96 Cu-0.06 Be-balance Zn No. 3; 1.66 Cu-0.07 Bebalance Zn No.4. 1.27 Cu-0.07 Be-balance Zn One inch diameter rods of each alloy were cast in graphite molds. 'cut from these rods, heated in the range, of 390-405 C. for one hour, and quenched in .water. Individual pieces were then heated for 2 hours at temperatures, with intervals of C.,

from 100" to 300 C. Maximum precipitationhardening (Rockwell B hardness) values resulted as follows: No. 1, 25 B for 200 C.; No. 2, 21 .B for 200 C.; No. 3, 15 B for 200 C.; No.4, 8 B for 150 C. An alloy of 2.47 Cu, 0.13 Be, remainder zinc treated similarly, gave a Rockwell B hardness of 26 B for 175 C. aging. The eifect of time at solution temperature up to 24 hours at 390 C. and .up to 24 hours for each aging temperature of 150. C., 175 C. and 200 C. indicated that the following heat treatments would be most satisfactory for the respective alloys:

Alloys 1, 2,3: 1 hr. at 390400 C. waterquench, age 4-hrs. 175 C. I I Alloy; 4: -1- hr. at 390-400" C. water quench, age Ah C. I The 1" diameter cast rods permitted cold swaging to diameter (about 40% cold reduction) for standard tensile bar stock. Standard tensile bars were machined from such stock Half-inch thick disks. were 1 after applying the above heat treatments in various combinations with 40% cold work. Results were as follows:

Standard tensile bar properties of rootstock Allo Prop. Tensile Percent No. Treatment limit strength elong.

As cast: 1 hr. 390 0., quench, 5, 000 12, 800 0 4 hr. 175 0. Cast, cold swaged 40%, heat 3, 700 20, 400 4 l treated.

Cast, 390 quench, swaged, 11, 500 38, 500 13 aged 4 hr. 175 0. Cast, heat treated, finally cold 11, 000 34, 500 7 swaged.

As cast: 1 hr. 390 0., quench, 8, 500 14, 850 0 4 hr. 175 0.

Cast, cold swaged 40%, heat 8,300 21,300 2 2 treated. 1

Cast 390 quench, swaged, 12,000 39, 800 23 aged 4 hr. 175 0. Cast, heat treated, finally cold 14, 500 38, 800 18 swaged. 7 As cast: 1 hr. 390 C., quench, 6, 500 I 15, 300 0 4 hr. 175 C. I Cast, cold swaged 40%, heat 4,900 19,300 2 3 treated.

Cast, 390 quench, swaged, 12, 000 35, 500 27 aged 4 hr. 175 0. Cast, heat treated, finally cold 13, 500 36, 400 19 swaged. I As cast: 1 hr. 390 C, quench, 3, 800 4,900 0 4 hr. 150 0. Cast, cold swaged 40%, heat 5,000 15, 400 1 4 treated. I

Cast, 390 quench, swaged, 13, 500 34, 200 14 aged 4 hr. 150 C. Cast, heat treated, finally cold 13, 500 34, 450 12 swaged.

, heat treatment. However, maximum elastic or Tensile properties always increase .with decrease'in cross section of the test piece. For this.

reason, standard strip tensile specimens (strip .04-06" thick). give tensile properties from 20 to 30% higher than are obtained for standard tensile bars, .505" in diameter) Hence, the tensile strengths from heat-treated and coldswaged bars of these new compositions are equal to (or slightly better than) the tensile properties of commercial alloy strip and it follows that strip material of the new compositions should be considerablybetter. v

The cast material, with practically no. ducti1-' ity, can be cold rolled only slightly without cracking even though it can be cold swaged fairly satisfactorily. These alloys do hot forge and hot roll easily in the temperaturerange of 300-350? C. The proper way to produce .high quality strip is to break down the structure of the cast billet by hot forging or hot rolling to a convenient intermediate oversize. The hot-worked material is then readilyhot or cold-rolled to the desired oversize previous to final heat treatment. The amount of final cold working, after complete precipitation treatment, determines the specific oversize previous to heat treatment- Thus to produce 60 mil strip with final cold reduction of 40%, the cast billet is hot worked and then hot or cold rolled to mils. The strip is then completely precipitation-hardened by the. spe cific heat treatment for its composition, and then the heat treated 100 mil strip is cold rolled 40% reduction to 60 mils.

Strip of fine quality is readily produced in this way. It is also possible to apply the final cold re-.

'duction to the strip after the 390 C. solution treatment and before the precipitation-aging treatment in the range of ISO- C. Good properties can also be achieved by cold rolling, strip after hot working and without any'further spring properties and maximum temperature stability as well as most efficient production nandling are conferred on these compositions by aperties of the treated and rolled strip of the four alloys, hereinbefore designated as alloys 1, 2, 3 and 4. Column 1 gives the alloy number. Columns 2 and 3 give the heat treatment previous to the final cold reduction shown in column 4. Column 5 states the second aging treatment, after final cold reduction, to determine the temperature stability of the developed properties. Columns 6, 7, 8, 9 give the resulting tensile properties.

in Cu content, is least aifected by heat treatment, softens at 150 C. and recrystallizes below 175 C.

5. Commercial alloys with similar Cu contents,

but lacking Be, are markedly inferior, particu larly in elastic properties and temperatures of recrystallization. The excellent properties of these new alloys are duetothe Be associated with In the table for strip properties, the materials, cold reduced by 40%, finished as strip 60 mils thick; those cold reduced by 60%, finished as strip 40 mils thick.

' These strip materials, in fully treated form will readily bend through 90 either with or transverse to the direction of rolling and will take an almost complete 180 bend without cracking. This indicates good formability for fabrication purposes. These materials in strip form, particularly alloys 1 and 2, possess spring properties. As a cantilever beam spring (supported at one end), a 4" length of 40 to 60 mil stock will with- Tensile properties of strip material Reference to the above table of tensile properties for strip material shows the following to be true:

1. Alloys 1 and 2 which have essentially the same composition do not recrystallize below 175 C. In fact, aging at 150 C. or 175 C. actually effects slight improvement in the proportional limits and yield strengths, With aging at 150 C. also resulting in an increase in ductility.

2. Alloy 3, containing 1.6% Cu (as compared with about 2% Cu in alloys 1 and 2), shows stability after aging at 150 C. but softens slightly after aging at 175 C. Fracture showed that it had not recrystallized at 175 C.

3. Alloy 4, containing 1.27% Cu, is quite stable up to 150 C. but has actually recrystallized at 175 C.

4. Alloy 4, cold rolled without heat treatment (line 17), possesses properties slightly better than those for present commercial alloys. The data for alloy No; 4 (lines 19 and 21) show the improvement in proportional limit and yield strength due to heat treatment. Alloy 4, lowest Allo Cold re- 1 hr. sec- Prop. 0.5% yield Tensile Per cent No. 1 S0111 treatment age duction 0nd aging limit strength st. elong.

1 1 405 C 175 C... 40 Room 15,000 32, 700 41, 750 15 2 175 C. 15, 000 32, 800 41, 600 15 3 60 Room. 14, 250 34, 000 46, 500 24 4 175 C 12,000 34, 000 42, 400 20 5 2 390 C 175 C. 40 Room.. 14, 500 31, 300 40,000 21 0 150 C 16, 000 33, 000 39,000 7 175 C... 15,000 32, 000 38, 200 20 8 60 Room 13,100 31,500 43, 500 18 9 150 C 14, 600 '31, 000 41, 500 27 10 175 C 14, 100 32, 650 40.000 7 ll 3 390 C 175 C Room... 14,500 30, 800 38,000 22 12 150 C 15,000 30, 700 35, 300 0 l3 175 0 11,300 28, 500 35,000 20 14 60 Room 12, 750 30, 000 43, 000 23 15 150 C 12, 800 26, 600 l 33 16 175 C 9, 700 24, 4.00 34, 600 28 17 4 Hot rolled at 300 C. 1. Room 9, 700 25,000 37,000 37 18 75" C. 7, 400 16, 400 26, 300 54 10 390 C 150 C 40 Room 11, 000 27, 500 35,000 20 20 175 C 6, 200 17,200 25, 000 5 21 Room 12, 400 26, 700 38, 500 32 22 150 C 12, 000 24,000 33, 700 34 23 175 C. 7, 800 16,000 25, 400 40 stand about 1" in deflection at the free end without permanent set or the marked flow characteristic of the present commercial alloys. The electrical conductivities of the new alloys are relatively high, for example in the range of 20 to 28% of that of pure copper, and are comparable with the conductivity of -30 brass. The cost of casting, heat treating and rolling the present alloys should be about the same as the cost for casting, annealing and rolling brass.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An alloy containing about .6 to 3% copper, .03 to .35% beryllium with the remainder substantially all zinc.

2. An alloy containing about 1 to 2.7% copper, .05 to .3% beryllium with the remainder substantially all zinc.

3. An alloy containing about 1.9 to 2.1% copper, about .05 to .15% beryllium with the remainder substantially all zinc.

4. A precipitation hardened alloy containing about 1 to 2.7% copper, .05 to .3% beryllium with the remainder substantially all zinc.

copper, about .05 :to .3% beryllium with the re mainder substantially all zinc.

8. A zinc basealloy containing more than .6% but less than 3%., copper, about .05 to .3% beryllium with the remainder substantially all zinc,

said alloy being characterized by a recrystallization temperature in excess of 175 C.

9. A zinc base alloy containing more than .6% but less than 3% copper, about .03% to 35% beryllium with the remainder substantially all zinc, said alloy being characterized by a .5% yield strength in excess of 30,000 pounds per square inch and a tensile strength in excess of 40,000 pounds per square inch.

10. A zinc base alloy containing more than .6% but less than 3% copper, about .05 to .3% beryllium with the remainder substantially all zinc, said alloy having been hot' worked and finally cold reduced about to 90%.

11. A method for improving the physical properties of a zinc base alloy containing copper and beryllium which comprises heat treating the alloy to effect a condition of precipitation therein and cold working the alloy.

12. A method for improving the properties of a zinc base alloy containing about 2% copper, about 0.1% beryllium with the remainder substantially all zinc which comprises precipitation hardening and subsequently cold reducing the alloy.

13. A method for improving the properties of zinc base alloys containing about 1.0 to 2.7% copper, about 0.05 to .3% beryllium with the remainder substantially all zinc which comprises reheating it at a lower :temperature to efiect precipitation in the alloy. r

14. Amethod for improving the properties of zinc base alloys containing about 1.0 to 2.7% copper, about .05 to .3% beryllium with the re:

mainder substantially all zinc which comprises heating the alloy from 1 to 24 hours at about- 350 to 405 C., quenching the alloy and reheat ing it for 1 to 24'hours at a temperature in the range of 100170 250 'C. i v

15. The process for improving the properties of a zinc base alloy-containing .6 to 3% copper, .03 to .35% beryllium with the remainder sub-- stantially all zinc which comprises hot working the alloy and thereafter cold reducing it about 10 to 16. The process for improving the properties of a zinc base alloy containing 1.0 to 2.7% copper, .05 to 3% beryllium with the remainder substan-. tially all zinc which comprises heating the alloy 1 to 24 hours at about 350 to 405 C., quenching the alloy, cold' reducing it about 10 to 90% and reheating it about to 250 C. for 1 to 24 hours.

17. The process for improving the properties of a zinc base alloy containing 1.0 to 2.7% copper, .05 to .3% berylliumwith the remainder substantially all zinc, heating the alloy 1 to 24 hours at 350 to 405 C., quenching the alloy, reheating at about 100 to 250 C. for 1 to 24 hours and thereafter cold reducing the alloy 10 to 90%.

18. The process for improving the properties 50f a zinc base alloy containing 1.0 to 2.7% copper, .05 to .3% beryllium with [the remainder sub-