US2023366A

US2023366A - Rolling extruded magnesium alloy

Info

Publication number: US2023366A
Application number: US609279A
Authority: US
Inventors: John E Hoy
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1932-05-04
Filing date: 1932-05-04
Publication date: 1935-12-03
Anticipated expiration: 1952-12-03

Description

Dec. 3, 1935. J. E. HOY 2,023,366

ROLLING EXTRUDED MAGNESIUM ALLOY Filed May-4, 1952 57 [7 iEy .5

INVENTOR JbhrLl Z Hay ATTORNEY Patented boo. s, 1935 UNITED; STATES PATENT ."OFFICE.

ao'umo' n'x'rnunnn MAGNESIUM ALLOY John a. Boy, Midland, Mich, assignor to m Dow Chemical Com corporation of Michigan Application May '4, 1932, Serial No. 609,279

In a copending application Serial No. 281,54 8, med May 29, 1928, now Patent No. 1,878,240, I

have described a method of, producing fabricated parts of um'or alloys thereof in which -um is a predominating constituent, by first-casting an-ingot of said metal followed by extruding the same in heated condition and then furthen shaping the extruded part by compresof the aforementioned method for the production stituent.

' Heretofore the production of flat metal stock alone? One example of the application of the method described therein shows the formation of a money propeller in which a cast ingot of thealloy is extruded from a die to form a blank and then the blank 18 0118110111170 the finished shape between compression dies in a forging press. Certain especial advantages of this procedure are the improved tensile strength and yield point obtained in the finished product;

The present invention relates tea-modification of fabricated magnesiumgor magnesium alloy 1 metal in the form of sheets'or plates or the like wherein the shaping operation is carried out by rolling anextrudedbillet of the metal. The terms mam m y a herein and in the appended claims to mean notoniy pure magnesium, but also alloys of the same wherein magnesium is the predominating consuch as sheets and plates of magnesium and its alloys has been based upon the method employing the well known steps of flr'stforming a rolling billet of'asuitabie volume of metal by casting and then rolling the same in heatedcondition inanumberofpassesaccordingtotheusualpractice of hot rolling metals. "While such a procedure may be'satisfactory for roiling'metals which I crystallize in the-cubic system, such as aluminum, iron, copper, etc., it is not wnouy satisfactory for metals which in the hexagonal system, such as magnesium and alloys thereof.

For example, when the magnesium or magnesium alloy rolling billet is heated to the temperature at which the metal reaches a suitable degreeof 7'plasticity, and rolling is commenced, the billet is liable to develop superficial cracks under the pressure of the rolls. In some instances these cracks are plainly visible while'in others the cracks are quite minute and are not evident on a visual inspectioni Orr-continuing the rolling operations, the cracks once formed in the metalremain therein, thusproducing sheets or plateswhich, due to such flaws, lack proper mechanical properties such as-tensile strength. Said cracks also pro- 'mote' corrosion where rolled metal is exr scum. (cuss-11.9

posed to atmospheric or other corrosive influences: During the rolling a certain amount of splitting or cracking also occurs at the edges of the rolled stock. These cracks vary in depth. measured from to a foot or more, and, once such a crack has formed,

the edge of the sheet, from about 0.5 inc further rolling usually results in'incre'asing the depth thereof. In order tominimize the tendency for such cracks to increase ell! depth, itisr customary to trim off the cracked edges prior to m each rolling pass. I These trimming operations notonly entail increased labor costs, but also resalt in a considerable wastage ofmetal, besides reducing the ultimate width of the sheet.

At present the only available method for over- 15 coming cracking and attendant defects is .to pro.-

- duce' relatively small percentage reductions in fllm'formed upon. the heated metal. Furthermore, each additional pass promotes further cracking at the edges, thus necessitating further 7 trimming which decreases the eflective width of sheet. Even when employing carefully regulated reductions at' each pass and the optimum working temperature, the ultimate mechanical properties of the resulting rolled metal-are not always equal to those obtainable by other methods of shaping magnesium and its alloys by compressive forces. In addition to such difficulties, it is generally necessary to machine off or otherwise obtain a smooth surface of cast billet before rolling in order to avoid producing an imperfect surface on the rolled product.

One object ofthe present invention is to provide a process of producing sheets orfplat'es of mafiie ium and its alloys in which. the aforementioned tendency to develop cracksis avoided. 45

Another obiect is to provide a rollingprocess in,

which the percentage thickness reduction per pass is greater than heretofore obtained. Other objects and advantages will appear as the description proceeds. To the accomplishment of 6 the foregoing andrelated ends, said invention, then, consists in the steps, methods, and procedures hereinafter fully described and particularly pointed out in the claims. The annexed drawing and the following description set forth in tie-. 3

tall but one oi. the various ways in which the principle of the invention may be carried out.

In said annexeddrawing:

Fig. 1 shows a cast ingotsuitable for extrusion; Fig. 2 is a vertical section through an extrusion apparatus; Fig. 3 is a section of an extruded billet; Fig. 4 is an end elevation of a rolling mill.

In Fig.2 is shown a billet container I, a die 2, end blocks 3 and [which prevent the displacement of the die, a ram 5 actuated by hydraulic or other suitable means, not shown. Placed within the bore of the container is an ingot G of a magnesiumalloy in the process of being extruded through the die into a billet 1, shown in section in Fig. 3.

In Fig. 4 is shown a pair'of cylindrical rolls 9 and I with journals supported in bearings II and l 2, the upper roll 9 being provided with screwdowns l3 which operate in the frames l4. Tables l and 16 are provided on. either side of the rolls. A rolling billet I1 is shown entering between the rolls, also a plate I 8 formed from the rolling billet by passing the same between the rolls.

The extrusion and rolling equipment shown are of conventional design and form no part of the present invention.

My invention is based upon the discovery of the fact that magnesium and its alloys may be shaped by compression using an apparatus such as a rolling mill without danger of fracturing the metal, if instead of employing cast metal stock, I employ the metal in the extruded condition as a starting point for rolling operations. I am enabled thereby also to reduce the number of passes under the rolls in obtaining a given thickness of metal, compared to the number of passes when cast metal stock is employed, and also to 1 dispense with a number of reheating operations.

The following examples will serve to show various preferred modes of carrying out 'my present invention and the improved eifect produced upon the structure and properties of the rolled extruded metal as compared to those of rolled cast metal. Example 1 Magnesium-manganese alloy, containing 1 to 1.5 per cent of manganese, balance magnesium.

(a) The alloy-was cast into an ingotand the sound sheet .was produced without cracking tensile strength 39,000 lbs./sq. in.

(b) The same alloy was cast into a rolling billet it" x 4" x 12" and rolled at 700 to 15o" F. using only 10 per cent reduction in thickness at each pass (greater thickness reduction than 10 per cent caused failure 01' the billet) to-a thickness of 0.10 inch. Properties of sheet:-the sheet produced showed superficial cracks and. edge cracking to a depth 01' 2 inches; tensile strength of part of sheet 35,000 lbs/sq. in.

Example 2 Magnesium-aluminum-ma'ng'anese alloy, containing6to8percentofaluminumand02to 0.3 per cent of manganese? balance magnesium. H '(a) The alloywas cast into an ingot and the ingot was extruded at 800 F. into a rectangular rolling billet 56 x 4" x 12". V The billet was then rolled into sheet at 700 to 750? with 15 per cent reduction in thickness at each pass, to

a thickneuot 0.10 inch. Propertiesot shoatz- 1 The b let was cracks. v

sound sheet was produced without cracking; tensile strength 37,600 lbs/sq. in.

(b) The same alloy was cast into a rolling billet /2" X 4" X 12" and rolled at 700 to 750 F. with only 10 per cent reduction in thickness at 5 each pass. Severe cracking occurred and sumcient sheet for test specimens was not available for tension tests.

7 Example 3 m Magnesium-aluminum-manganese alloy, containing approximately 4 per cent of aluminum and approximately 0.3 per cent of manganese, balance magnesium.

(a) The alloy was cast into an ingot and the ingot was extruded at 800 F. into a rectan ular rolling billet x 4 x 12". The billet was then rolled into sheet at 700 to 750 F., with 15 per cent reduction in thickness at each pass, to a thickness of 0.10 inch. Properties of sheet:- sound sheet free from cracking was produced; tensile strength 36,700 lbs/sq. in.

(b) The same alloy was cast into a rolling billet x 4" x 12" and-rolled at 700 to 750 F. into sheet employing 10 per cent reduction in thickness at each pass. Properties of' sheet:- severe edge cracking occurred as well as superficial cracking; tensile strength test specimens were not available owing to the unsoundness oi the sheet.

Example 4 Magnesium aluminum cadmium.- zinc alloy, containing the said metals in the following approximate amountsz-magnesium 97 per cent, aluminum 1 per cent, cadmium 1 per cent, zinc 1 per cent. 1

(a) The alloy was cast into an ingot and the ingot was extruded at approximately 800 F. into a rectangular rolling billet x 4" x 12" and 40 rolled into sheet 'at approximately 750 F. employing abouta 30 per cent reduction in thickness at each passto a thickness of 0.10 inch. Properties of sheetz- -sound sheet was produced without cracking.

(b) The same alloy was cast into a rolling billet /z" X 4" X 12" and'rolled at approximately 750 F. employing about a 30 per cent reduction inthickness at each pass to a thickness 01 0.10 inch. Properties of .sheet:--sheet developed I Example} Magnesium-tin-zinc alloy, containing appmx- .imately 4 per cent of tin, 1 per cent of zinc, balance magnesium.

. (a) The alloywas cast'into an ingot and the ingot was extruded at approximately 800 F. into a rectangular rolling billet x4" x 12" and rolled into sheet at approximately 750 Remploying about a 30 per cent reduction in. thickness at each pass to a thickness of 0.10 inch. Properties of sheet:sound sheet was produced without (b) The same alloy was cast into arolling pil let /2" X 4" x 12" and rolled at approximately 750 F. into sheet employing about a 30 percent reduction in thickness at each pass to a thickness of 0.1 inch. 1 Properties of sheet:sheet developed cracks during the rolling.

Example 6 v Magnesium-tin-zinc manganese alloy, containmg approximately 4 per cent of tin, 1 per cent of (a) The alloy was cast into an ingotx-and'the ingot was extruded at approximately 800 F. into a rectangular rolling billet X 49 12" and rolled at approximately 750 F. intofsheet employing about a 30 per cent reduction in th.ick-"' ness at each pass to a thickness bf 0.1 inch. Properties of sheet:--sound sheeti was obtained, free from cracks.

(b) The same alloy was cast into a rollingbillet x 4" X 12" and rolled at approximately 750 F. into sheet employing about a 30 per cent reduction in thickness at each pass to a thicktors and is to be chosen in accordance with the naness of 0.1 inch. Properties of sheetz-cracks developed during the rolling operations.

In carrying out my improved process for producing rolled metal I may proceed with the steps thereof already mentioned which include the 1 three operations, viz., (1) casting, (2) extrusion, (3) rolling, in the maner set forth below. Step (1), for example, may be carried out by casting the metal in sand or metal molds according to any satisfactory method for casting magnesium. Following the casting step, the ingot may be subjected to heat treatment, in which the metal is maintained at from about 400 C. to a temperature below the melting point of the most fusible constituent of the alloy for from one-half to twenty hours, in accordance with the processes described in United States Patents Nos 1,712,988, 1,712,989, and 1,712,990, although such procedure is not essential.

The cast ingot, heat treated or otherwise, is extruded at a suitable temperature. This may be accomplished by inserting a cast magnesium alloy ingot (Fig. 1), previously heated, into the container i of the extrusion apparatus and then applying pressure to the ingot, as shown in Fig. 2,

by means of the ram 5 so as to extrude a billet,

I through the die 2. As is well known in extruding magnesium base alloys, the pressure required for extrusion decreases with increasingtemperature, while the mechanical properties of the extruded metal are usually the better the lower the temperature of extrusion. Furthermore, the composition of the alloy is a factor and it is preferable to employ extrusion temperatures below the melting point of the most fusible con-- stituent thereof. The temperature, therefore, at which the rolling billet may be extruded will be a comprise between the above-mentioned facture of the alloy employed. For magnesium base alloys (those having a magnesium content in ex-- cess of 75 per cent) suitable temperatures in general will lie between 500 and 950'F., while preferred temperatures are between 700 and 850 1". Following the extrusion operation, I may employ .an'other heat treating step as above described.

Ordinarily, however, the rolling operation may be carried out directly after extrusion, provided the metal is preheated to the rollingtemperature.

The extruded-rolling billet, heat treated as above described or otherwise, is then rolled. The rolling operations consist of passing the rolling billet between the rolls of a mill repeatedly so as to produce a reduction in thickness at each peated passes is shown at it reduced in thickness. The temperature at which the metal is to be rolled is dependent upon the alloy composition 5 and is to be chosen in accordance with the proportions and kind of alloying metals present with magnesium as a base. In general, a temperature of from 425 to 850 F. is suitable in most instances. The reduction'in thickness .per pass is adapted to the plasticity of the alloy. A reduction of approximately to per cent may be produced per pass, but I do not wish to limit myself to any specific per cent reduction inasmuch as the reduction per pass varies with the composition of the alloy and other factors.

While I have described my invention more particularly in terms of the formation of sheet metal, I wish it, to be understood that I do not limit myself thereto inasmuch as my new improved method of shaping magnesium and its alloys may finished product having a uniform cross section,

for example, strip metal, rods, bars, channels,

and the like, such shapes, as is well known, may be obtained by employing suitably profiled rolls for the rolling operation. For the cylindrical rolls shown'in the drawing by way of illustration, therefore, may be substituted any other suitable rolls, such as profiled rolls.

Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the method and the steps herein disclosed, provided those stated by any of the following claims or 85 their equivalent be employed.

I therefore particularly point out and distinctly claim as my invention:-

1. In a method of producingmolled shapes of magnesium or an alloy thereof, the steps which 40 consist in casting an ingot of said metal, extruding said ingot into a billet at a temperature between 500 and 950 It, and rolling said extruded billet at a temperature between 425 and 850 F. I

2. In a method of producing rolledshapes of magnesium or an alloy thereof. the steps which consist in extruding an ingot of said metal-into a billet, and rolling said billet. I 3. In a method of producing rolled shapes of magnesium, or an alloy thereof, .the'steps which consist in extruding an ingot of said metal at a temperature between 500 and 950 F., and rolling said extruded billet at a temperature between 425 and 850 1".

4. A process of producing rolled articles from as magnesium and high percentage magnesium