US2870051A

US2870051A - Method of heat treating aluminum bronze alloy and product thereof

Info

Publication number: US2870051A
Application number: US641457A
Authority: US
Inventors: John F Klement
Original assignee: AMPEO METAL Inc
Current assignee: AMPEO METAL Inc
Priority date: 1957-02-21
Filing date: 1957-02-21
Publication date: 1959-01-20
Anticipated expiration: 1976-01-20

Description

United States Patent i 2,870,051 Mnrnjon or HEAT TREATING ALUMINUM BRONZE ALLOY AND PRODUCT THEREOF John F. Klement, Milwaukee, Wis., assignor to Arnpco Metal, Inc., Milwaukee, WiSL, a corporation of Wisconsln No Drawing. Application February 21, 1957 Serial No, 641,457

5 Claims. c1. us -21.92)

This invention relates to an aluminum bronze alloy having an increased modulus of elasticity and to a method of producing the same. This application is a continuation-in-part of the application, Serial No. 371,192, filed.

Ju-ly 29, 1953, entitled Aluminum Bronze Alloy Struc ture and Methodof Making the Same of the same inventor, now abandoned.

It is an accepted engineering fact that the modulus of elasticity of a material cannot ordinarily be changed any appreciable amount by heat treatment. However, the present invention is based on the discovery that certain metallographic phases of aluminum bronze, namely the duplex (alpha and beta) structure or the beta structure, can be heat treated in a manner to alter the modulus of elasticity. For certain specific applications of aluminum bronze, such as shafting, bushings or machine members where an increase of rigidity is desirable,- the heat treat-. ment of the present invention can be most effectively used to substantially increase the modulus of elasticity.

An object of the invention is to provide an aluminum bronze alloy having a substantiallyincreased modulus of elasticity over the normally accepted value and which is particularly adaptable for use as shafting, rolls or bush-v ings requiring high rigidity. I

Another object is to provide a method of increasing the modulus of elasticity of an aluminum bronze alloy ,while also improving the other physical properties such as hard ness, yield strength and modulus of rigidity. 7

Another object is to provide a heat treatment for a duplex phase aluminum bronze alloy whichserves to substantially increase the modulus of elasticity of the alloy while retaining .3 sufficient ductility for structural design.

Other objects and advantages will appear in the course of the following descriptionz' i T o carry out the present invention the aluminum bronze alloy to be heat treated should have a certain metallographic structure, namely a duplex structure, consisting of alpha and beta phases, or a beta structure. I I

The me allog aphi st u of a p ticul r alum nu bronze is apt to vary depending on the alloying elements included therein. The ordinary aluminum bronze composed of aluminum and copper and substantially free of other alloying elements, will require above 9.5% aluminum in order to possess the preferred alpha and beta metallographic structure. An aluminum content in an ordinary aluminum bronze of below 9.5% will generally result in the alpha phase alone which will not bring about the desired change in modulus of elasticity when sub jected to thepresent heat treatment. I 7

An aluminum content of over 12% in the ordinary 2 aluminum bronze will result in the beta phase, which, as in the case of the duplex structure, is preferred. The aluminum concentration may be as high as- 20% in the normal practice.

When the chemicalcomposition ofthe aluminum bronze is altered by the addition of alloying elements, the proportion of aluminum required to obtain the duplex or beta structure may correspondingly vary. For example, it a metal having an aluminum absorbing power, such as iron, nickel, manganese or cobalt, is employed in the alloy, it may then be necessary to add as much as 16% by weight of aluminum to get the preferred alpha and beta structure. With the small amounts of these alloying additions normally employed, the necessary aluminum content may be in the neighborhood of about 10.5% by weight of the alloy.

A typical illustration of an alloy composition containing aluminum absorbing power ingredients and possessing a duplex structure is as follows:

Percentage by weight Aluminum t 10.5 Iron 7 3.5 Copper Balance In contrast to this composition, a lower aluminum content may be employed in order to obtain the duplex or beta structure when tin or silicon are present in the alloy. These materials tend to increase the formation of the beta constituent, and act very much like aluminum inproducing a second phase.

It is therefore possible to employ as little as 3% aluminum by weight when using substantial amounts of tin or silicon and obtain the duplex structure. An illustration of an aluminum bronze alloy containing small amounts of aluminum and having the duplex metallographic structure is as follows:

Percentage by weight 3 The presence of alloying elements in a duplex or beta aluminum bronze structure will not greatly alter the reaction of the bronze alloy during heat treatment. However, in some cases, it may take a longer period of time to produce the necessary metallographic change in the alloy during heat treatment to produce a satisfactory increase or decrease in the accepted modulus of elasticity.

The present invention is directed to a heat treatment to be applied to a duplex or beta phase aluminum bronze alloy to obtain the gamma constituent in suflicient proportions and distribution to give a substantial increase in the modulus of elasticity.

For commercial feasibility, the gamma constituent should be present in the range of about 3 0% to by weight of the alloy. A gamma content outside of this range will adversely affect the physical properties of the alloy and decrease the usefulness of the alloy for commercial and structural purposes.

Examples of aluminum bronze alloy compositions in weight percent to which the heat treatment of the invention can be applied to increase the modulus of elasticity are as follows:

C D E F G balance "fiifi' balance balance balance The heat treatment consists of initially heating the alloy to a temperature of over 1050 F. and preferably in the neighborhood of about 1450 F. The alloy is maintained at this elevated temperature for a period of about one hour and generally for a period of about minutes to 30 minutes per two inch section of the alloy.

After the heating treatment, the alloy is quenched at a rate of 500 F. to 1000" F. per minute per two inch section to a temperature in the range of about 200 to 400 F. It is necessary that the quench be made at the above rate for if thequench is slower than 500 F. per minute, too much alpha is obtained which will not transform to the gamma constituent during the subsequent treatment. Conversely, if the rate of quench is faster than 1000 F. per minute, too much beta is obtained in the metallographic structure which results in too great a proportion of the gamma constituent in the final alloy. This results in the alloy being extremely brittle. It has been found that a cooling range of about 600 F. per minute is satisfactory for most applications.

The cooling may be accomplished by means of oil or water quenching or any other suitable fluid to produce the above mentioned cooling rate.

The resulting structure after cooling when using a duplex phase structure, is generally alpha face centered cubic crystal with a beta matrix which is a martensitic structure. This phase has a body centered cubic lattice.

After the alloy has been conditioned properly by the elevated temperature treatment and cooled, it is necessary to reheat the alloy in av series of temperature increments to a temperature of about 850 F. to 950 F. to obtain the gamma constituent in the desired proportions and distribution to provide the increased modulus of elasticity.

In the reheating treatment, it is necessary to heat the alloy from the quenched temperature to at least one intermediate temperature below the range of 850 to 950 F. and to hold the alloy at this temperature for a substantial period of time in order to produce a uniform gamma;, distribution in the alloy. It has been found that low temperature heating substantially below the 850 to 950 F. range causes nucleazation of the gamma and produces a uniform distribution of gamma throughout the structure. It has also been found that the greater the number of temperature increments involved in the reheating, and the accompanying holding period at these temperatures, the more homogeneous the gamma constituent becomes.

As an example of the reheating treatment, the alloy, after quenching, is heated to a temperature in the range of 490 F. to 550 F. and held at that temperature for a period of 45 minutes to 90 minutes per two inch section of the alloy. After this holding period is completed, the alloyis further heated to a temperature in the range of 675 F. to 725 F. and held at this temperature for a period of 45 minutes to 90 minutes per two inches of section.

After this second increment of heating, the alloy is then further heated to a temperature in the range of 850 to 950 F. and held at this temperature for a period of one to two hours per two inches of section of the alloy. As previously pointed out, there should be at least one increment of heating or soaking before reaching the 850 to 950 F. temperature range and preferably two or more increments of heating and holding at that temperat re.

After the reheating operation, the alloy is furnace cooled to a temperature in the range of 550 to 650 F. and held at this temperature for 20 to 45 minutes per two inches of section. The alloy is then cooled to room temperature.

Ordinarily the modulus of elasticity of commercial aluminum bronze alloys is shown at 15,600,000 p. s. i. With the treatment of the present invention it is possible 1 to increase the modulus of elasticity above 20,000,000

p. s. i. to a value of 24,000,000 p. s. i.

To obtain a substantial increase in the modulus of elasticity and yet retain an appreciable ductility, the alloy should contain the alpha and beta duplex phase. The beta phase or martensitic structure present after the quenching operation acts to bring about an increase ir the modulus of elasticity during the subsequent aging, while the alpha phase serves to give the treated alloy the necessary ductility for structural purposes.

If the alpha phase alone is present in the alloy, the modulus of elasticity will not be altered by the heat treatment. Conversely, if only the beta phase is present the modulus may be substantially increased but the elongation isappreciably reduced. Thus, for the most purposes the duplex phase is preferred with the proportion of the alpha phase to the beta phase depending upon the elongation desired in the treated alloy.

With a duplex structure and a properly controlled chemical composition of alloying elements and the controlled heat treatment of the invention, it is also possible to have attractive other properties when the modulus of elasticity is changed. For example, by employing the present treatment with a selective chemical analysis, comprising 10.6% aluminum, 3.6% iron, 2.5% nickel and the balance. copper, the modulus of elasticity can be substantially increased to 24,000,000 p. s. i. and the alloy will have a tensile strength of over 100,000 p. s. i., a yield strength of over 60,000 p. s. i., an elongation of a 4% minimum, and a Brinell hardness of approximately 235. Thus, it is possible by employing the described heat treatment and the proper alloying elements to produce a substantially increased modulus of elasticity together with improvements of other physical properties, when so desired. An alloy exhibiting these properties would be particularly adaptable for use as shafting, bushings or machine members requiring high rigidity.

While the above described heat treatment is directed to maintaining the alloy at given temperature ranges for specified periods per two inch section of the alloy, it is intended that the time period is to be proportionately increased for sections greater than two inches and pro portionately decreased for sections less than two inches.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

1. A method of increasing the modulus of elasticity of an aluminum bronze alloy having from 3% to 20% aluminum and having a beta constituent in the metallographic structure, which comprises heating the alloy to a temperature of over 1050 F., cooling the alloy at a rate of 500 F. to 1000 F. per minute per two inch section to a temperature below 400 F., and reheating the alloy with at least one increment of temperature to a temperature in the range of 850 F. to 950 F., said alloy being held at the temperature of the increment and at the temperature in the range of 850 to 950 F. for a sufiicient period of time to obtain the gamma constituent in the range of about 30% to by weight of the alloy and thereby produce a substantial increase in the modulus of elasticity.

2. A method of increasing the modulus of elasticity of an aluminum bronze alloy containing from 3% to 20% aluminum and having at least some beta phase in the metallographic structure, which comprises heating the alloy to a temperature of over 1050 F., quenching the alloy at a rate of 500 F. to 1000 F. per minute per two inch section to a temperature in the range of 200 F. to 400 F., and reheating the alloy from the quenched temperature to at least one intermediate temperature below the range of 850 F. to 950 F., holding said alloy at said intermediate temperature for a period of 45 minutes to 90 minutes per two inch section of the alloy continuing the reheating of the alloy from the intermediate temperature to a temperature in the range of 850 F. to 950 F., holding said alloy at the temperature in the range of 850 F. to 950 F. for a period of one hour to two hours per two inch section ofthe alloy, said reheating serving to produce the gamma constituent in the alloy in the range of 30% to 70% by weight of the alloy and thereby produce a substantial increase in the modulus of elasticity of the alloy.

3. A method of increasing the modulus of elasticity of an aluminum bronze alloy containing from 3% to 20% aluminum to produce at least some beta phase in the metallographic structure, which comprises heating the alloy to a temperature of over 1050 F., cooling the alloy at a rate of 500 F. to 1000 F. per minute per two inch section to a temperature below 400 F., reheating the alloy to a temperature in the range of 490 F. to 550 F. and holding the alloy at said last named temperature range for a period of 45 minutes to 90 minutes per two inch section of the alloy, heating the alloy to a temperature in the range of 675 F. to 725 F. and holding the alloy at said last named temperature range for a period of 45 minutes to 90 minutes per two inch section of the alloy, and heating the alloy to a temperature in the range of 850 F. to 950 F. and holding the alloy at said last named temperature range for a period of one to two hours per two inch section of the alloy, said reheating treatment producing the gamma; constituent in the range of about 30% to 70% by weight of the alloy to thereby substantially increase the modulus of elasticity of the alloy.

4. A method of increasing the modulus of elasticity of an aluminum bronze alloy containing from 3% to 20% aluminum and having at least some beta phase in the metallographic structure, which comprises heating the alloy to a temperature of over 1050 F., quenching the alloy at a rate of 500 F. to 1000 F. per minute per two inch section to a temperature in the range of 200 F. to 400 F., reheating the alloy from the quenched temperature to a temperature in the range of 850 F. to 950 F. in a series of temperature increments, said alloy being held at each temperature increment for a period of minutes to 90 minutes per two inch section of the alloy and said alloy being held at the temperature in the range of 850 F. to 950 F. for a period of one hour to two hours per two inch section of the alloy, cooling the alloy to a temperature of 550 F. to 650 F., maintaining the alloy at said last named temperature range for a period of 20 minutes to 45'minutes per two inch section of the alloy, and further cooling the alloy to room temperature.

5. An aluminum bronze alloy containing from 3% to 20% by weight of aluminum and having a modulus of elasticity in the range of 21,000,000 p. s. i. to 24,000,000 p. s. i. and being characterized by having from 30% to by weight of the gamma constituent in the metallographic structure, said alloy being produced by heating the alloy to a temperature of over 1050 F., quenching the alloy at a rate of 500 F. to 1000 F. per minute per two inch section to a temperature in the range of 200 F. to 400 F., and reheating the alloy from the quenched temperature to a temperature in the range of 850 F. to 950 F. in a series of temperature increments, said alloy being held at each temperature increment for a period of 45 minutes to minutes per two inch section of the alloy and said alloy being held at the temperature in the range of 850 F. to 950 F. for a period of one hour to two hours per two inch section of the alloy, said reheating serving to produce the gamma constituent in the alloy in the range of 30% to 70% by weight of the alloy and thereby increase the modulus of elasticity to the aforementioned range.

References Cited in the file of this patent Aluminium Bronze, issued by the Copper Development Assoc. (London), N0. 31 (1939), pages 31-60.

Metal Progress, vol. 38, July-Dec. 1940, pages 791, 793, 794, 797.

Claims

1. A METHOD OF INCREASING THE MODULUS OF ELASTICITY OF AN ALUMINUM BRONZE ALLOY HAVIG FROM 3% TO 20% ALUMINUM AND HAVING A BETA CONSTITUENT IN THE METALLOGRAPHIC STRUCTURE, WHICH COMPRISES HEATING THE ALLOY TO A TEMPERATURE OF OVER 1050*F., COOLING THE ALLOY AT A RATE OF 500*F. TO 1000*F. PER MINUTE PER TWO INCH SECTION TO A TEMPERATURE BELOW 400*F., AND REHEATING THE ALLOY WITH AT LEAST ONE INCREMENT OF TEMPERATURE TO A TEMPERATURE IN THE RANGE OF 850*F. TO 950*F., SAID ALLOY BEING HELD AT THE TEMPERATURE OF THE INCREMENT AND AT THE TEMPERATURE IN THE RANGE OF 850 TO 950*F. FOR A SUFFICIENT PERIOD OF TIME TO OBTAIN THE GAMMA2 CONSTITUENT IN THE RANGE OF ABOUT 30% TO 70% BY WEIGHT OF THE ALLOY AND THEREBY PRODUCE A SUBSTANTIAL INCREASE IN THE MODULUS OF ELASTICITY.