United States Patent Office 3,146,096 Patented Aug. 25, 1964 3,146,096 WELDABLE HIGH STRENGTH MAGNESIUM BASE ALLOY George S. Foerster, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich, a corporation of Delaware No Drawing. Filed Nov. 23, 1962, Ser. No. 239,829 4 Claims. (Cl. 75-168) These alloys combine moderate strength, good Workability in the wrought form, and are usable both for sheet and extrusions. Certain of these alloys have good weldability but in many applications must be stress relieved after welding to avoid stress corrosion cracking. Other alloys such as, for example,

ZelOA (l.3Zn+0.2mischmetal) and AZlOA (1.25Al+0.4Zn) have been employed as substitutes where weldability without stress relief was required, but only at a sacrifice of other desirable properties such as, for example, tensile and compressive yield strength.

The principal object of the present invention therefore, is to provide a magnesium base alloy having in community the properties of weldability without the need.

for stress relief, good workability, and desirable strength.

Known art teaches in general that if the concentration of the non-magnesium constituents in a magnesium base alloy system of the magnesium-aluminum-zinc type containing manganese is increased, properties such as, for example, tensile and compressive strengths are, within limits, correspondingly increased. It has now been surprisingly and unexpectedly discovered, however, that by reducing the aluminum and zinc concentrations of the alloys of magnesium base-aluminum-zinc-type containing manganese, below those conventionally employed and by adding small amounts of calcium thereto, alloys are obtained possessing the above and other advantages in a combination heretofore not available in any one of the known magnesium base alloys within the aforementioned alloy system.

The present invention, then, resides in a magnesium base alloy consisting by weight essentially of from about 0.1 to about 1.75 percent aluminum, from about 0.05 to about 0.6 percent zinc, from about 0.2 to about 1.0 manganese, and from about 0.05 to about 0.6 percent calcium, the balance being magnesium, wherein the maximum concentration of calcium to be employed is in an inverse relationship with the concentration of zinc used according to the formula:

Wt. percent Ca=1.42 (zinc percentage) Although the aluminum concentration in the alloy need not be maintained in any relative proportion with any of the other alloy constituents, if high extrusion speeds are desired, suchas, for example, 50 to 100 f.p.m., generally the aluminum content must be limited in an inverse relationship with calcium; that is, if either the aluminum or calcium concentration within the above respective ranges is high, the other of the two must be in a relatively low concentration. For example, it was found desirable to limit the aluminum content to about 0.5 percent in order to obtain high extrusion rates when calcium was at a concentration of about 0.3 percent. To obtain optimum extrudability, that is, high strength at high extrusion speeds, in the alloy of this invention it was found that the aluminum content should be 0.2 to 0.5 percent, the zinc content about 0.2 to 0.5 percent, the calcium content from 0.2 to 0.4 percent, and the manganese content about 0.5 percent, the balance being magnesium.

The amount of aluminum relative to calcium in the alloy under this invention, however, has little effect on hot rollability and can be as high as about 1.75 percent, whereas the amount of zinc relative to calcium must be maintained according to the aforementioned equation. However, good rollability can be obtained where the alloy contains relatively high amounts of calcium if the zinc content does not exceed about 0.3 weight percent, but at higher zinc concentrations, calcium must be limited by the said aforementioned equation to avoid cracking during hot rolling.

Good creep resistance in the alloy of the invention was found to be obtainable, along with good workability, in the combination wherein the concentration of the constituents in weight percent are about 0.4 for aluminum, about 0.3 for zinc, about 0.5 for manganese, and about 0.3 for calcium.

On the other hand, the alloy of this invention exhibits good workability and ductility when the alloy composition consists essentially of about 1.2 percent aluminum, about 0.3 percent zinc, about 0.5 percent manganese, and about 0.2 percent calcium, the balance being magnesium.

Manganese is added to the alloy of the present invention to enhance strength. The so added manganese also enhances corrosion resistance.

The present invention provides an alloy of flexible utility useful in applications requiring an alloy of moderate to high strength plus weldability without the need of stress-relief, possessing good workability such as, for example, in extruding and rolling, and in addition, being dilute in alloying constituent concentrations, it thereby offers economy along with utility.

The following examples serve to illustrate further the present invention:

A number of magnesium base alloys in accordance with the present invention and others as blanks for comparison were prepared using conventional foundry alloying and melting techniques as practiced in the magnesium art and tested in various ways as shown hereinafter. Some of the so-prepared alloys were cast into 3 inch diameter billets, and others into 2 by 4 by 8 inch rolling slabs. The billets were extruded into a 1A by inch strip at varying speeds from a 3 inch container at about 700 F. Samples of the extrusions were tested both asextruded and after having been aged for 24 hours at 350 F.

The slabs were hot rolled to about a 0.1 inch thickness at about 850 F. in a multitude of passes (with reheating as necessary to avoid cracking). The so-rolled sheet was then annealed for one hour at 900 F., quenched in water, and cold rolled close to the cracking limit. The sheet was then heat treated one hour at 300 F. and 700 F. Further, some of the same and other specimens were hot rolled and heat treated one hour at 950 F., quenched in Water, and aged 24 hours at 350 F.

Samples of all of the above preparations were tested 4 properties obtained when the hot holled sheet was subsequently solution heat treated, quenched, and aged as indicated showing improved ductility and tensile strength.

TABLE IV Creep Extension 1 Extension (in percent) subsequent to loading was measured at periodic intervals of time. The values of creep extension in Table IV were determined after a time of 100 Example Percent Percent Percent Percent Percent A Zn Ca Mn Creep hours.

1 In 100 hours at 300 F., stress at 5 kilo-pounds per square inch.

TABLE I Die x strip extrusions at 700 F. from a 3 billet 20 rpm. 7100t.p.m. Percent Percent Percent Percent Percent Percent Example Al Zn Ca Mn E IYS CYS TS Percent CYS TS TYS (Blank). 0. 5 4v 0 0.39 0. 6 Cracked at f.p.m. (Blank) 0. 5 2.0 0.40 0. 0 Cracked at 10 f.p.m (1) 0. 5 0. 5 0.33 0. 6 14 25 19 38 12 27 20 39 (2) n 0. 3 0. 5 0. 34 0. 6 14 26 20 39 10 19 15 35 (3) 0. 3 0. 2 0.29 0.0 12 27 21 40 14 25 19 38 (4) 0. 2 0. 4 0.20 0.0 13 27 18 39 13 78 19 40 1 Aged 24 hours at 350 F.

In Table I where Example Number 1 is compared with the examples therefollowing, it is clearly shown that good extrudability is, in general, obtained in the alloy of the present invention when the relative amounts of either zinc or aluminum, within their respective ranges, are inversely related. That is, Example Number 1 shows that excessive zinc causes cracking at low extrusion speeds, whereas, when the concentration of zinc is within its specified range and in a proper amount with respect to aluminum, the extrusion process can be carried out at a relatively rapid Table IV illustrates the good creep resistance of the alloy of the present invention, particularly when calcium with respect to aluminum is low.

I claim:

1. A weldable high strength magnesium base alloy consisting by weight essentially of from about 0.1 to about 1.75 percent aluminum, from about 0.05 to about 0.6 percent zinc, from about 0.2 to 1.0 manganese, and calcium in an amount of from about 0.05 to about 0.6 percent but not greater than 1.4 minus 2 times the percentage of zinc concentration, the balance being magrate without cracking of the extrude. nesium.

TABLE II 1 300 F.1 hour 700 F.1 hour Percent Percent Percent Percent Example Al Zn Ca Mn Pcrltcnt TYS CYS 'IS Percent TYS CYS TS (Blank) 0. 5 4.0 0.39 0.0 (Blank) 0. 5 2v 0 0. 40 0. 6 Cracked during hot rolling (Blank) O. 5 1. 0 0. 31 0. 6 (5) 0. 3 0. 2 0.29 0. G 2 38 34 44 18 22 19 35 l. 0 0. 6 0. 15 0. 6 4 37 34 44 22 23 18 35 0. 5 0. 2 0. 32 0. (i 2 41 30 47 13 24 18 36 0. 5 0. 5 0. 33 0. 6 4 41 36 48 12 25 19 3G 0. 5 0. 2 0. 56 0. 6 2 43 40 20 24 20 37 1 Hot rolled at 850 F., annealed 1 hour at 900 F., quenched, cold rolled, then heat treated as indicated.

TABLE I11 Per- Per- Per- Per- Per- Example ecnt cent cent cent cent TYS CYS TS Al Zn Ca Mn E 1 Hot rolled at 850 F., solution heat treated 1 hour at 950 F., quenched, aged for 24 hours at 350 F.

Table III also representatively shows the excellent 2. An extrudable and weldable high strength magnesium base alloy consisting by weight essentially of from about 0.2 to about 0.5 percent aluminum, from about 0.2 to about 0.5 percent zinc, about 0.5 percent manganese, and calcium in an amount of from about 0.2 to about 0.4 percent, the balance being magnesium.

3. A creep resistant and weldable magnesium base alloy consisting by weight essentially of about 0.4 percent aluminum, about 0.3 percent zinc, about 0.5 percent manganese, and about 0.3 percent calcium, the balance being magnesium.

4. A workable and weldable magnesium base alloy consisting by weight essentially of about 1.2 percent aluminum, about 0.3 percent zinc, about 0.5 percent manganese, and about 0.2 percent calcium, the balance being magnesium.

References Cited in the file of this patent UNITED STATES PATENTS 2,185,452 Wood Jan. 2, 1940