US3617395A

US3617395A - Method of working aluminum-magnesium alloys to confer satisfactory stress corrosion properties

Info

Publication number: US3617395A
Application number: US814631A
Authority: US
Inventors: Francis P Ford
Original assignee: Olin Corp
Current assignee: Olin Corp
Priority date: 1969-04-09
Filing date: 1969-04-09
Publication date: 1971-11-02
Anticipated expiration: 1988-11-02
Also published as: BE763560A

Abstract

Providing an aluminum-magnesium alloy containing from 5.0 to 10.0 percent magnesium, heating said alloy to a temperature range of 650* to 800* F. for 1 to 16 hrs., cooling said alloy. heating said alloy to a temperature range from 225* to 375* F. for 15 mins. to 24 hrs., cooling said alloy to ambient temperature, cold reducing said alloy to 5.0 to 95.0 percent reduction, heating said alloy to a temperature range to 225* to 375* F. for 15 mins. to 24 hrs., and cooling said alloy.

Description

United States Patent Inventor Francis P. Ford Hamden, Conn. Appl. No. 814,631 I Filed Apr. 9, 1969 Patented Nov. 1, 1971 Assignee Olin Mathleson Chemical Corporation METHOD OF WORKING ALUMINUM- MAGNESIUM ALLOYS TO CONFER SATISFACTORY STRESS CORROSION PROPERTIES Claims, 1 Drawing Fig.

U.S. Cl 148/1 1.5 A, 148/ l 2.7 Int. Cl C22f l/04 Field ofSearch [48/] 1.5, 12.7

[56] References Cited UNITED STATES PATENTS 3,346,371 /1967 Jagaciak l48/l1.5 3,346,372 10/1967 Jagaciak l48/l 1.5

Primary Examiner-L. Dewayne Rutledge Assistant Examiner-W. W. Stallard Anorneys Robert H. Bachman, Richard S. Strickler, Donald R. Motsko and Thomas P. ODay EFFECT OF DlgPLEXSHB/L/ZMF TREATMENTOF WPE COLDROLL 1 2707' X dfiDl/R-f COLDROLL 1 27D! XII'DURS ONSTRESS CORROSDN PROPERTIES OFAL- 73m -Q2ZCR- aooaza ALLOY,

HEAf/NG 8 COOL/N6 RATES/N HEAT TREATMENTS JJ F/I-DUI? so 7 a g l u k g; 8 40 kt Q 1 o 1 a s 5 a a a s f: s fi E E '50 'tr 5 l w b g g Q 0 u u a o 55 8 f 7 g 8 5 E '1' '0 40 a 190 s Q E. t I 3 kn 8 e t --Z0 0 Q 50 75 02 l 8 09 a0 cowmr/amr can not 0 50 do STAB/HI TREATMENT. 0 I0 I a0 40 S TRLSS CORROSION LIFE -HOURS w w w M m H n a H M INVENTOR ATTORNEY am w FRANCIS I? FORD kco/vmv IOML com ROLL sma/uzz TREATMENT.

S TRESS- CORROSION. LIFE -HOUR$ PATENTED uuvz l97l EFFECT OF DQPLEX SHE/LUNG TREATMENTOF TYPE COLD ROLL f 270?" x 4HOUR COLD ROLL f 270/ x 4l-DURS 0N STRESS CORROSDN PROPERTIES OF AL- 776016 0.2% R- 0.00828 ALLOY, v HEAT/1V6 & cooulva RATES w HEAT TREATMENIS'. 33F/ HOUR OVERALL TEMPERS I 11-80 MNQ\QSPW QZOQMM MQOKMQ EORUDQHQ QQQU m METHOD OF WORKING ALUMINUM-MAGNESIUM ALLOYS TO CONFER SATISFACTORY STRESS CORROSION PROPERTIES The present invention relates to a new and improved method of producing aluminum-base alloys containing magnesium. More particularly, the present invention resides in aluminum-base alloys containing from about 5.0 to about percent magnesium and characterized by improved stress corrosion resistance due to the improved partitioning of a magnesium-rich phase between the grain boundaries and the grain matrixes, i.e., to a different volume ration thereof.

The advantages to be derived from alloying magnesium with aluminum-base alloys were recognized very early in the development of aluminum technology. Consequently, the aluminum-magnesium series of alloys is one of the oldest used commercially.

It is well known, however, that magnesium in aluminumbase alloys if present in an amount more than about 3 percent sensitizes the alloy to stress corrosion. Retention of magnesium in solid solution is readily achieved by annealing the alloy at a temperature above the solvus temperature and cooling at a rate rapid enough to prevent precipitation of a magnesiumrich second phase. The alloy may then be cold worked to final gauge. However, due to natural aging at ambient temperature magnesium retained in solid solution in excess of about 5.0 percent by the rapid cool tends to precipitate preferentially in the grain boundaries as an aluminum-magnesium intermetallic .compound thus sensitizing the alloy to stress corrosion.

Furthermore, the mechanical properties of the cold-worked alloy tend to degrade during service due to thermal recovery, which also occurs at or near ambient temperature.

In order to prevent degradation of the mechanical properties, it is necessary to stabilize the alloy after the final coldworking step at a temperature somewhat above that which it will be subjected to in service. Thus, the alloy will not undergo subsequent change of mechanical properties at temperatures significantly below the stabilizing temperature.

As is well known, some improvement in resistance to stress corrosion may be obtained if the alloy is slowly cooled, i.e., less than 500 F. per hr., after the finalanneal prior to cold working to promote heterogeneous nucleation of the equilibrium magnesium-rich phase in the grain matrix as well as in the grain boundaries, rather than solely or predominately in the grain boundaries as will occur upon aging of the alloy. The stabilizing treatment, however, in those alloys containing more than 5.0 percent magnesium causes additional heterogeneous nucleation of the equilibrium magnesium-rich beta phase, or a metastable beta modification, in the grain boundaries and, should the alloy be highly cold worked, at points of threedimensional disregistry in deformation bands.

Precipitation of the aforementioned magnesium-rich phase preferentially in the boundaries causes susceptibility to stress corrosion which increases with increasing magnesium content. As a result, the magnesium content of the aluminum-magnesium alloys is generally limited to about 5.5 percent magnesium, thus precluding favorable strength properties at magnesium contents in excess of 5.5 percent.

Accordingly, it is a principal object of the present invention to provide a new and improved process whereby stress corrosion susceptibility in the aluminum-magnesium alloys is substantially reduced, and the alloys produced thereby.

lt is-a still further object of the present invention to provide a convenient and expeditious process as aforesaid at reasonable cost.

Further objects and advantages of the present invention will appear hereinafter.

The process of the present invention comprises; (A) providing an aluminum-magnesium alloy containing from about 5.0 to about l0.0 percent magnesium, balance essentially aluminum, (B) heating said alloy to a temperature range of from about 650 to 800 F. for from about 1 to 16 hrs., wherein the rate of heating from about 350 F. is not greater than about 50 F. per hr., (C) cooling said alloy wherein the rate of said cooling is not greater than about 50 F. per hr. to about 350 F., (D) prestabilizing said alloy in a temperature range of about 225 to about 375 F., for about 15 min. to 24 hr., (5) cooling said alloy to ambient temperature, (F) cold reducing said alloy to about 5.0 to about 95.0 percent reduction, (G) stabilizing said alloy in a temperature range of about 225 to about 375 F. for about 15 min. to 24 hr., and; (H) cooling said alloy.

Normally, the heating up and cooling-down rate to and from the prestabilization and stabilization treatments is about l5 to 50 F. per hour in commercial practice. The present invention however is not restricted in this respect and higher or lower heating rates may be readily employed. It is to be further noted that the alloy preferably is provided in cold-reduced form in step A.

Although the heating range for the thermal stabilization temperature is generally in the order of 275 to 300 F. the present invention is applicable to other temperatures as may be dictated by conventional mill practices,'i.e., 225 to 375+ F.

In an alternative embodiment of the present invention an additional cold reduction may be provided prior to step D. Thus, the alloy may be cold reduced from about 5.0 to about 95.0 percent reduction prior to the prestabilization treatment.

The drawing shows that for the overall tempers of H-34, H- 36 and "-38 corresponding to 40 percent, 60 percent and percent cold reduction respectively, that the stress corrosion properties are greatly improved from the unsatisfactory values obtained when a conventional full anneal followed by a cold roll and stabilization is employed.

The data in the drawing indicates that in general the improvement in stress corrosion resistance increases, in the case of metal provided in cold-reduced form as in the alternative embodiment, with the amount of the final cold roll, i.e., step F, for any given temper. It is also seen that optimum increase in stress corrosion resistance is achieved in accordance with the preferred embodiment, omitting the cold roll just prior to the prestabilization treatment. In this illustration the prestabilization and stabilization treatments were both conducted at a temperature range of 270 F. for 4 hr., and with the heating and cooling rates at about 33 F. per hour to simulate actual commercial practice wherein coil annealing furnaces are employed.

Naturally other elements may be present in the aluminummagnesium alloys as alloying additions or impurities. Common alloying additions may include but are not limited to the following: boron in an amount from 0.001 to 0.35 percent; chromium in an amount from 0.05 to 0.3 percent; indium in an amount from 0.002 to 0.80 percent; gallium in an amount from 0.0l to 0.50 percent; cadmium in an amount from 0.03 to 0.50 percent; thorium in an amount from 0.005 to 0.350 percent; misch metal in an amount from 0.005 to 0.30 percent; tellurium in an amount from 0.005 to 0.30 percent; lithium in an amount from 0.0l to 0.80 percent; germanium in an amount from 0.0l to 0.55 percent; cobalt in an amount from 0.10 to 0.80 percent; copper in an amount from 0. l0 to 0.60 percent.

Naturally small amounts of elements may also be present in the aluminum-magnesium alloys as impurities. Impurities may include but are not limited to the following; iron up to 0.50 percent; silicon up to 0.50 percent; copper up to 0.25 percent; manganese up to 0.35 percent; zinc up to 0.2 percent; titanium up to 0.l5 percent; beryllium up to 0.02 percent; and others in total up to 0.2 percent.

The present invention is of considerable commercial importance in relation to high magnesium containing alloys. As shown in the drawing conventional fabrication of such wrought alloys gives unsatisfactory stress corrosion resistance while the method of the present invention provides for a satisfactory stress corrosion life with an adequate safety margm.

The present invention will be more readily apparent from an consideration of the following illustrative examples.

EXAMPLE I An alloy having the following composition was prepared from a charge of commercial purity aluminum, master alloys of iron-aluminum, chromium-aluminum, beryllium-aluminum, titanium-aluminum and the other alloying additions in elemental form. The alloy was cast in the form of 45Xl6 l20- inch ingots.

TABLE I Mg Cr Fe Si Cu Mn Zn Ti Be B Alloy. 7.47 0.19 0.26 0.10 0.06 0.01 0.01 0.002 0.005 0.007

EXAMPLE ll EXAMPLE Ill This example shows the results obtained in accordance with the present invention and shown in the drawing.

Following hot rolling to the intermediate gauges the alloys were cold rolled to 0.060 inch, employing various amounts of reduction prior to the prestabilization and stabilization treat-v ments. It may be seen however that all the alloys in the 40, 60, and 80 percent cold-reduced condition obtained the greatest resistance to stress corrosion when the alloys were cold rolled directly from the intermediate gauges to the final gauge of 0.060 inch prior to the stabilization treatment, i.e., when the additional cold roll prior to the prestabilization treatment was not provided, in accordance with the preferred embodiment of the present invention. It is seen that significant improvement was still obtained, however, with the prior cold roll at various reductions when contrasted with the conventional cold roll and stabilizing treatment although the improvement was not as great as in the aforementioned preferred embodiment.

EXAMPLE IV Stress corrosion testing of the alloy of example I after the treatments of examples ll and Ill was conducted in the following accelerated manner:

Samples 0.060X2.0X0.25 inch were stressed at 80 percent of their yield strength in a 6 percent solution of NaCl +0.005M' NaHCO,. An anodic current of 11 ma./sq. in. was applied via platinum gauze cathode. A failure time of 13 hr. in the accelerated tests corresponds to a failure time for preformed U-band specimens in a marine environment of greater than 3 years, a limit which normally signifies a stress corrosion resistant condition.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.

What is claimed is:

A. Providing an aluminum-magnesium alloy containing from 5.0 to l0.0percent magnesium.

B. heating said alloy to a temperature range of 650 to 800 F. for 1-6 hr., the rate of said heating not greater than 50 F. per hr. from 350 F.

C. cooling said alloy, the rate of said cooling not greater than 50 F. per hr. to 350 F D. heating said alloy to a temperature range of from 225 to 375 F. for 15 min. to 24 hr.,

E. cooling said alloy to ambient temperature,

F. cold reducing said alloy from 5.0 to 95.0 percent reduction,

G. heating said alloy to a temperature range of from 225 to 375 F. for 15 min. to 24 hr.,

H. cooling said alloy.

2. A process according to claim 1 wherein said alloy is cold reduced from 5.0 to 95.0 percent reduction following step C and prior to step D.

3. A process accordingto claim 1 wherein said alloy contains an alloying substituent selected from the group consisting of 0.001 to 0.350percent boron, 0.05 to 0.3 percent chromium, 0.002 to 0.80 percent indium, 0.01 to 0.50 percent gallium, 0.03 to 0.50 percent cadmium, 0.005 to 0.350 percent thorium, 0.005 to 0.30 percent misch metal, 0.005 to 0.30 percent tellurium, 0.01 to 0.80 percent lithium, 0.01 to 0.55 percent germanium, 0.10 to 0.80 percent cobalt, 0.10 to 0.60 percent copper and mixtures thereof.

4. A process according to claim I wherein said alloy contains as an impurity an element from the group consisting of iron up to 0.50 percent, silicon up to 0.50 percent, copper up to 0.25 percent, manganese up to 0.35 percent, zinc up to 0.2 percent, titanium up to 0.15 percent, beryllium up to 0.02 percent, total all others up to 0.2 percent, and mixtures thereof.

5. A process according to claim 1 wherein said alloy contains 6.0 to 8.0 percent magnesium, 0.001 to 0.350 percent boron, 0.05 to 0.3 percent chromium and as impurities iron up to 0.5 percent, silicon up to 0.5 percent, copper up to 0.25 percent, manganese up to 0.35 percent, zinc up to 0.2 percent. titanium up to 0.25 percent, beryllium up to 0.02 percent, total all others up to 0.2 percent.

* i i i i UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 617,395 Dated November 2, 1971 ln fl Francis P. Ford It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading, line 5, after Nov. delete "l" and insert 2 Golunm 2, line 19, after 375 delete and insert Column 2, line 47, after "5 insert O Column 3, line 21, after "produce" insert alloys Column 4, line 17, delete "6" and insert l6 Signed and sealed this 18th day of April 1972.

(SEAL) A ttest:

EDWARD I LFLETCHIUR ,JR ROBERT GOT'ISCHALK Attesting Officer Commissioner of Pfitents RM PO'WSO H069) USCOMM-DC scam-s69 n U 5 GOVERNMENT FHINING OF'ICE 1969 0-356-334

Claims

2. A process according to claim 1 wherein said alloy is cold reduced from 5.0 to 95.0 percent reduction following step C and prior to step D.
3. A process according to claim 1 wherein said alloy contains an alloying substituent selected from the group consisting of 0.001 to 0.350percent boron, 0.05 to 0.3 percent chromium, 0.002 to 0.80 percent indium, 0.01 to 0.50 percent gallium, 0.03 to 0.50 percent cadmium, 0.005 to 0.350 percent thorium, 0.005 to 0.30 percent misch metal, 0.005 to 0.30 percent tellurium, 0.01 to 0.80 percent lithium, 0.01 to 0.55 percent germanium, 0.10 to 0.80 percent cobalt, 0.10 to 0.60 percent copper and mixtures thereof.
4. A process according to claim 1 wherein said alloy contains as an impurity an element from the group consisting of iron up to 0.50 percent, silicon up to 0.50 percent, copper up to 0.25 percent, manganese up to 0.35 percent, zinc up to 0.2 percent, titanium up to 0.15 percent, beryllium up to 0.02 percent, total all others up to 0.2 percent, and mixtures thereof.
5. A process according to claim 1 wherein said alloy contains 6.0 to 8.0 percent magnesium, 0.001 to 0.350 percent boron, 0.05 to 0.3 percent chromium and as impurities iron up to 0.5 percent, silicon up to 0.5 percent, copper up to 0.25 percent, manganese up to 0.35 percent, zinc up to 0.2 percent, titanium up to 0.25 percent, beryllium up to 0.02 percent, total all others up to 0.2 percent.