US2381219A - Aluminum alloy - Google Patents

Description

Patented Aug. 7, 1,945

as smor Ira M. Le Baron, Arnold, pa, mm, to Aluminum Company of America, Pittsburgh, Pa, a corporation of Pennsylvania No Drawhlg. Application @ctobcr H2, 2042,

Serial No. 181,721

(oi. ssss) 6 Claims. This invention relates to aluminum base alloys and more particularly to aluminum base alloys containing substantial amounts of copper and small amounts of other specific alloying elements for improving the tensile properties oi the alloy in'the heattreated and precipitation hardened condition.

Aluminum-copper alloys, particularly those laluminum base alloys containing between 1 and 12 per cent copper. have found fiide application in industry and have been used in large quantiare, however, certain uses for which these alloys are employed, which require exceptionally high tensile properties together with good resistance ties. Although these alloys in either the as-cast per alloy refers to an aluminum alloy containing copper as thepredominant added alloying element. The terms heat treatment and solution heat treatment as used herein signi y a treatment wherein an alloy is heated to a temperature below the fusion point of the lowestmeltlng eutectic of the alloy .for a time sumcicntly long to dissolve a substantial portion of the soluble alloying constituents. Artificial aging is a treatment given to precipitation hardeningalloys, wherein the alloy' is heated to a temperature somewhat above room temperature but below the heat treating temperature to precipitate the alloying ingredients present in the aluminum in a supersaturated condition, a condition produced to corrosion and good working and machining characteristics. Furthermore, these high. properties whether in the cast or'wrought alloy must remain relatively stable over long periods of time under all operating conditions. A notable example of the uses requiring alloys having the foregoing properties is found in the fabrication of dustry are generally easily met and the properties remain within relatively narrow limits indefl-' nitely so that good performance of these light alloys'is obtained; however, constant effort is being madeto improve them in order that the current minimum requirements will be greatly exby rapidly cooling the alloy from the solutionheat treating temperature. The term tensile properties includes tensile and yield strength, elongationandoithealloy. The present invention is predicated on the discovery that the tensile properties and resistance to corrosion of. solution heat treated and arti-. flcially magnesium l'ree aluminum base alloys containing copper are greatlyimproved by the addition to those alloys of about 0.01 to 2.0 per cent of llthiumandat least one of the'ele-- ments selected from-the group, which for conveniencemay be called thocadmium group. con-' sisting of cadmium, mercury, silver, tin. indium and zinc, these elements being present in the proportion of about 0.01 to 1.5 per cent each of cadmium, mercury, silver, tin, indium, and about 0.01 to 0.5 per cent of zinc, the total of these elements not exceeding about 1.6 per cent. The combination of lithium and one or more of the elements "from the above group in the aluminum-copper It is an object of the present invention. to p o- 4 vide a heat treatable aluminum base alloycontaining appreciable amounts of copper, having high'tensile properties'and good resistance to properties by heat treating and aging. 'Still an other object of my invention is to provide aluminum base alloys containing appreciable amounts of copper, which possess good working and machining characteristics together with high ten silo properties and good resistance to corrosion.

The term aluminum base alloy as used throughaluminum by weight. The term aluminum-copcorrosion. Another object of the present invenalloys has the surprising eifect of improving the tensile properties and resistance to corrosion to.

. an extent much greater than the aggregatlve,

eflect of the same elements present separately in'the alloys. Lithium is not known to have any pronounced beneficial eiiect on the tensile properties or the alloy when not in combination with the elements'oi' this group and it is sometimes i even detrimental to the tensile properties; how-' ever, lithium with one or more elements from the cadmium group forms a combination which exerts an unexpected and profound influence on the properties of aluminum-copper alloys. and furthermore,-to achieve the obiects of the present invention lithium must be present in all combinaout the specification and appended claims refers to an alloy containing at least '10 per centmetallic tions of elements from the foregoing group. lithium should be present in the alloy in amounts not less than 0.01 per cent to consistently obtain any substantial lint in properties, and

easilyhandledduringproductionofthealloyand. it does not have any particular detrimental ef- 2 V I assure group. Bilver, however, which is founr? adjacent thisgroup ischaractericed by many-of the propertiescommcn tothemetalsofthisgroup. From the eifect displayed by the elements of the cadmium group on the aluminum-copper alloys and from the disclosurein Doanand Mahla,theseelements must necessarily be considered as a group.

' Lithium which flils in the "light metals M fectsonthealloyifthemaxlmumlimit'iseb' ceeded. Cadmiummaybepresentinthealloy in amounis from 0.01 to 1.5 per cent but-the most pronounced increase in tensile properties 'occurswhenitlspresentin amcimtsbetween0m and0.5percent,andaboveaboutl.5percent thereispracticallyncincreaseinpmerfl thegroupususllyhavethe greatestinnu: onthetensile' properties. 'l'he.lithium-cad-- combination is the only exception to Whenmorethan'onemetalfromthegroup The elements of the group which form Moll! with lithiumandim I 4 I. prove propertiesof aluminum-copper alloys are also a natural in which are elements g a number of similar chemical and physical properties, as

for example, densiiy'melting point, strength andamnity for omen. is shown in the periodic 0." Here all the metals in my group. except silver. are mm in the flow melting hea y'metals" [of this periodic system is definitely diiierent in many of its physical and chemical properties from ,the elements in the low melting heavy metalsgroup, and therefore cannot be considered in the class with the elements in'that group."

The alloysto which the addition of lithium and one or more of the elements of the aforementioned group is particularly beneficial are those containing 1 to 12 per centicopper, not

more than 1 per cent each of silicon and iron present as lm ties, and with or without a'total of 0.01 to 1.5 cent of one or more of the hardening elementsmanganesechromium, titanium, molybdenum, tungsten, vanadium, nickel, cobalt, beryllium and boron within the following'proportions for each of said elements: manganese, 0.05 to 1.5 per cent: chromium, 0.05

1 per cent; titanium, 0.03 to 0.5 per cent; molybdenum, 0.05 to 1 per cent; tungsten, 0.05 to 1 per cent; vanadium, 0.01 to 1 per cent; zirconium,

0.05to 0.5 per cent; nickel 0.05 to 1 per cent; cobalt, 0.05 to l per cent; beryllium, 0.01 to 0.5 per cent; and boron, 0.01 to 0.5 per cent. The foregoing hardeningelements constitute a group of substances all but the last two ofwwhich are in the "high. melting heavy metals" group of the table in the book by Dean and Mahlapreviously,

referred to, and which. for the purposesof my invention, are alike inrespecttotheirhardening f effect upon the alloys of aluminum copper-lithium and one or more metals from the cadmium group. Although beryllium and boron arefnot found in the high melting heavy metals group of this-table, they have high melting points together witha number of characteristics similar to the metalsin the high melting heavy metals group. All the above named elementsserveto enhance particular properties -oi the alloy without substantially altering its fundamental characteris- -,tics. 'lhe'pieferredrangeforcopperinthesealloys isbetween 8 and 5 per cent.

The term magnesium-free alloys as herein employed refers to those alloys which have less than 0.01 per cent magnesium present as animpurity. Since magnesium has a definite detrimental eifecton thetensile properties of my allow. it is desirablein commercial practice to keep this-impurity below a maximum of 0.00.5

per cent. g

.lhe solution and aging treatments for alumihum-copper 'alloys containing lithium and one or more metals from the cadmium group arenot materially different from the convenflonal treatments given to aluminum-copper alloys, i. e., a solution treatment wherein the alloy is heated to a temperature suillcientiy highand for a period of time suillciently long to dissolve the soluble constituents. This heat treatment is conventionally carried out for aluminum-copper alloys at a between 550-1000 I". for a period of timehetween 15 minutes and 8 home. The alloy isthenquenched'andsrtiflcialiy'aged. In the aging treatmait the quenched alloy is'held at a temperature between250and400' l'.for4t o20 hours. No special conditions or equipment are requiredto heat treat and age myali ya The lmprovementinaluminum-copper alloys addition of lithium and one or more metals from the cadmium group occurs in either the cast or wrought alloys and in addition to the high tensile properties and resistance to corrosion, these alloys possess good machining and workingc'haracteristics. v

The effect of the combination of lithium and an element selected from the cadmium group on the tensile properties of aluminum-copper alloys may be illustrated from the following observations. An aluminum base alloy nominally containing 4.5 per cent copper, 0.8 per cent manganese, 0.25 per cent silicon and 0.15 per cent iron was melted and divided into three portions, one

portion being used as a standard of comparison, 1 and lithium and cadmium being added to one of the remaining portions, and lithium, cadmium and silver being added to the other remaining portion. The amounts of lithium, cadmium and silver in these portions areindicated in the table below. The ingots from each portion were poured under similar conditions and then rolled into sheet about 1 inch in thickness, Six standard test specimens were machined from each sheet and all were heat treated at 980 F. for minutes, quenched in cold water :and then artificially aged 12 hours at 320 F. The tensile properties of the alloys from each portion as shown by the average results from tests made on the specimens are listed in the following table:

Per cent Per cent Per cent Percent Tensile Yield 1 Alloy oi Ll of Cd of Ag elon ain alloy in alloy in alloy m l. None None .None 57, 000 35, 000 18. 0 2 1.0 0.15 None 82.195 75,900 ,7.8 3 1.0 0.15 0.15 80,650 74.500 7.5

from all three portions, the beneficial eifect of lithium-cadmium and lithium-cadmium-silver combinations on the tensile properties of heat treated and artificially aged aluminum-copper alloys is apparent.

' The claims whereinv thephrase the balance substantially all aluminum" is employed include the elements, particularly the hardening elements, which are frequently added to aluminum base alloys toimprove certain specific properties and also the usual impurities of iron and silicon.

I claim:

1. A magnesium-free aluminum base alloy conot the testsmade onthe specimenstaining from 1 to 12 per cent copper, from 0.01

to 2 per cent lithium, from 0.01 to 1.5 per cent to 2 per cent lithium,

zinc.

0.01 to 2.0 per cent lithium,

characterized by a higher tensile and yield strength in the 'heat treated .and aged condition than the same alloy not containing both lithium and cadmium.

2. A magnesium-tree aluminum base alloy containing from 1 to 12 per cent copper, from 0.01 from 0.01 to 0.5 per cent zinc and the balance substantially all aluminum, said alloy being characterized'bya higher tensile and yield strength in the heat treated and aged condition than the same alloy not containing both lithium and zinc.

3. A magnesium-nee containing from 1 t6 12 per cent copper, from 0.01 to 2 per cent lithium, from 0.02 to 1.5 per cent total of cadmium and zinc, the zinc not exceeding about 0.5 per cent, and the balance substantially all aluminum, said alloy being characterized by a higher tensile and yield strength in the heat treated and aged condition than the same alloy not containing lithium, cadmium and 4. A magnesium-free aluminum base alloy containing from 3 to 0.01 to 2.0 'per cent lithium, at least one of the elements selected from a group consisting of cadmium, mercury, silver, tin, indium and zinc, these elements being present in the proportion of about 0.01 to 1.5 per .cent each of cadmium, mercury, silver, tin, indium, and about 0.01 to 0.5 percent of zinc, the total of these elements not exceeding about 1.5 per cent, and the balance substantially all aluminum, said alloy being characterized by a higher tensile and yield strength in the heat treated and aged condition than the same alloy not containing both lithium and at least one of the metals from said group.

5. A magnesium-tree aluminrn base alloy containing from 3 to 5 per cent copper, from 0.01 to 2 per cent lithium, from 0.01- to 1.5 per cent cadmium and the balance substantially all aluminum, said alloy being characterized by a higher tensile and treated and aged condition than the same alloy not containing .both lithium and cadmium.

6. A magnesium-tree aluminum base alloy containing from 1 to 12 per cent copper, from at least one of the selected from a group consisting of mercury, silver. tin, indium and zinc, these elements being present in the proportion of about 0.01 to 1.5 per cent each of cadmium, mercury, silver, tin, indium, and about 0.01 to 0.5 per cent 01' zinc, the total of these elements not exceeding about 1.5 per cent, and the balance substantially all aluminum, said alloy being tensile and yield strength in the heat treated and aged condition than the same alloy not containing both lithium cadmium,

and at least one of the metals from said group.

m M. LE BARON.

aluminum base alloy 5 per cent copper, from yield strength in the heat'