US2064323A - Process of forging magnesium and high percentage magnesium alloys - Google Patents

Description

1936. w. SCHMIDT ET AL v PROCESS OF FORGING MAGNESIUM AND HIGH PERCENTAGE MAGNESIUM ALLOYS Filed July 29, 1931 INVENTORS ATTORNEYS Patented nee. is, 1936 UNITED STATES PATENT; i oF F cE PROCESS OF FORGING AND HIGH PERCENTAGE MAGNESIUM ALLOYS Walter Schmidt and Hubert Altwicker, Bitterfeld,

Germany,

ors, by mesne assignments, to

Magnesium Development Corporation, a corporation of Delaware Application July 29, 1931 Serial No. 553,822 In Germany August 16, 1930 8 Claims. The present invention relates to a process of forging magnesium and high percentage magnetained by working magnesium and-magnesium alloys are extensively oriented ,crys tallographi cally. Such forgings thus necessarily vary in their capacity for resisting stresses, of differing 15 direction, particularly as regards the ratio between the yield point of the forging under elongation and compression respectively. This is probably attributable to the peculiar conditions v of deformation (translation, or twinning) of the individual hexagonal crystals of the metal. A

capacityfor resisting high stresses in only one direction is undesirable in a forging, since, ordinarily, the finished forging is subjected'to stress components of differing direction. This leads to the problem'of producing forgings of magnesium, and magnesium alloys, whose capacity for resisting tension and compression stresses, as far as practicable, is the same in all directions.

The present invention relates to a process for the production of magnesium forgings which 30 have, as closely as possible, the same resistaiice to tension'and compressionstresses in every direction. According to the present invention theorientation ofthe mechanical properties in mag nesium forgings is suppressed to a substantial\ 35 extent by forging in such a manner that, during the deformation of the original'ingot, the flnal shape and dimensions of the forgings are approached by stages, and by interposin'g, between thoseindividual stages which serve to lead to thedesired final shape, stages in which the forging is effected by blows in a direction at right angles to the direction of the blows effecting the main direction of deformation in view of the final v 45 shape. Of course, themain direction of deformation must alwaysremain predominant; but the interposed changes. of forging direction at right angles to the main directionprevent excessive crystallographic orientation, check slip of the crystals and/or retard twinning. In this way, a gradual approximation of the final shape is obtained; When, as is possible, the final shaping .l, i; i eflected by swaging' or die-pressing, it is advisable to select the lowest temperature pos- 53 slble (having in mind the shape of the die) so ,as

to prevent recrystallization of the irregular crystalline structure produced by the previous opera- 1; ons. a

' As a further advantage of the present invention, the forging process itself is facilitated. Since, in the case of magnesium and its alloys,' the deformation substantially occurs by translation of the basal plane, continued deformation in one and the same direction would in combination with the uniform orinetation of. the crystals taking place under such deformation, lead, in a relatively short time, to a condition in which the arrangement of the individual crystals would hinder any further deformation in the same direction. This unfavourable eifect is counteracted, in the present invention, by the opposingstages of directional deformation so that the finishing of the forging is facilitated. It is particularly ad,- visable, in cases where the final shaping step is performed in a die, to select. as the last deforma- 20 tion stage prior to swaging or die-pressing, a stage in which the direetion of deformation is opposed to thedesired main directon of deformation in the die. If, for example, it is desired to form, in

the die, an annular body, the dimensions of which are greater radially than axially, it is advisable to so forge the work piece that elongation in the radial direction takes place during die-pressing (the final stage of deformation) By this means the flow of the metal in the radial direction, when .in the die, is substantially-facilitated.

In order to clearly describe the nature of the present invention, reference is made to the accompanying drawing, which illustrates diagramtically and by way of example a typical em- 5 t ent of the process of the present invention. ferring tofthedrawing Fig. l is a view in elevation of a blank under deformation and rep resentsthe first stage of the process; Figures 2a and 2b, respectively, illustrate a lateral andh: an axial view of the piece, obtained from that sho, in Figure l, in the second stageof the process.

In Figs. 1, 2c and 2b, the broken lines indicate the shape of the block when the particular stage in question is started, whereas the full lines represent the final shape of the block on termination of such stage; and Figure 3 represents a side view of .thefinal shape of the object.-

Referring to Fig. l, a is. the original blank, which is first' forged, by an upsettingoperation (see arrow 1' indicating the direction-of deformation), into a body shaped as at b. As will be seen from the drawing, this upsetting operation serves to compress the original blank or billet so as to produce radial outward flow of the ll directions substantially normal to the direction of the applied force f. This body b is then turned through and, while being continuously rotated on itsaxis (see Fig. 2b and note the arrow j indicating the direction of rotation) is deformed in a direction which is trans verse to the original direction of deformation by repeated blows in a direction shown by arrow 1 thus efiecting an elongation of the upset block. Due to the continuous rotation of the body b on its axis, the blows applied in the direction indicated by arrow 1 are effective to apply radial pressure at a plurality of points of the previously deformed billet (body b), and it will be noted that such radial pressure is applied in a directionwhich is always substantially parallel to the directions of metal flow in the initial compressing operation shown in Fig. 1. By several repetitions of these operations, namely alternate up settingand elongation, the upsetting being always slightly predominant, a body of the form shown in Fig. 3 is finally obtained, the mechanical properties of which are substantially the same in the direction a, g/ and z. The final shape isthen imparted to this body by forging in the die. Several examples of the application of the process of the present invention will now be given.

Example 1 For producing a forged crank case for a radial engine, a known magnesium alloy containing about 8 percent of aluminium may be employed. In such a piece it is necessary that the capacity for resisting stress, both as regards tension and compression, should be as closely as possible the same in all directions. A crude ingot, 300 mms. in diameter and 600 mms. high, is cast from this alloy and is then upset, as an upright cylinder, at 280-400 0., in the forging press, until the height has been reduced by 30 percent. The ingot is then turned on its axis, through 90 from the original direction, and the deformation is continued, by forging transversely to the first direction of deformation, the ingot being continuously rotatedon its. original axis,

until the diminution produced in the original height of the cylinder in both operations is reduced to about 15 percent. The ingot is then again turned through 90, and the forging is continued in the same way, by alternate upsetting and elongation, though, in view of the final shaping, the upsetting predominates in each case. After the original height of the cylinder has been reduced by about 70 per cent in this manner, the final shapingis effected in the-die at 280 C. The result attained by this process is that the flnishedpiece exhibits practically the same elongation yield point both in the direction of the original cylinder axis and at right angles thereto, namely about 16-18 kgs. per square millimeter. Atthe same time the compression yield point is very near the tensile yield point, having been ascertained to be 14-16 kgs. per square millimeter in both directions.

Example 2 mechanical properties at right angles to its axis, because the transverse or oscillatory stresses occurring at the hub act in that direction. Hence, the highly stressed portion in the vicinity of the hub is formed in stages, by alternate forging in directions differing by right angles, with gradual approximation to the final shape, in the man- 'ner described in Example 1. In the case of the blade, too, the forging is performed by alternate elongation, upsetting and broadening. The final shaping, particularly as regards the pitch of the propeller blade, is effected, in a known manner, by pressure in the die.

We claim: I

-1. A process of forging magnesium and high percentage magnesium alloys which comprises the steps of compressing a'billet so as to produce radial outward flow of the metal in all directions substantially normal to the direction of the applied force, and applying radial pressure at a-plurality of points of the deformed billet and substantially parallel to the directions of metal flow in the initial compressing operation so as to compensate for. themajor part of the deformation produced in the first step.

2. A process of forging magnesium and high percentage magnesium alloys which comprises the steps of compressing a billet so as to produce flow of the metal in a direction to produce the shape desired, and applying pressure to the deformed billet substantially parallel to the direction of metal flow in the initial compressing operation so as to compensate for the major part of the deformation produced in the first step. v

3. As a new article of manufacture, a forged blank of metal, in which magnesium largely predominates, having the substantially unoriented crystal grain structure throughout characterizing magnesium which has been compressed to flow the metal radially outward and thereafter subjected to pressure substantially parallel to the directions of metal flow in the initial compressing operation, said blank by virtue of the unorienated crystal structure being further characterized by a resistance to mechanical stresses substantially equal in all directions. I

4. As a new article of manufacture, a forged blank of metal, in which magnesium largely predominates and containing about 8 per cent of aluminum, said blank, having the substantially unoriented crystal grain structure throughout characterizing magnesium which has been compressed to flow the metal radially outward and thereafter subjected to pressuresubstantially parallel to the directions of metal flow-in the initial compressingoperation, said blank by virtue of the unoriented crystal structure being further characterized by a resistance to mechanical stresses substantially equal in all directions.

5. A process of forging magnesium and high percentage magnesium alloys in stages which comprises subjecting a billet to forging stages in which the billet is compressed so as to produce flow of the metal at substantially right angles to the compressive forces, and in a direction to produce the shape desired, and interposing between said forging stages intermediate forging stages in which pressure is applied to the deformed billet substantially parallel to the direction of metal flow inthe first-named forging stages, the deformation produced by said inter mediate forging stages compensating for the major part of the deformation produced in the said first-named forging stages am s 1 flJiprocessofforgingmagnesiumandhlah percentage magnesium alloys in stages which comprises subieoting a billet to forging stages in whiohthebilletiscompressedsoastoproduce flow of the metal at substantially risht angles to the compressive forces, and in a direction to'produce the shape desired, and interposing' between i said forging stages intermediate forging stages in which pressure is applied to the deformedbillet substantially parallel to the direction of metal flow in the first-named forging stages, the

deformation produced. by said intermediate-forgingstages c'ompensating'for the major part of the deformation produced in the said firstnamed' forging stages; the final stage of deformation, being effected at the lowest temperature compatible with lastic deformation.

7. A process 0 forging magnesium. and high percentage magnesium alloys in stages which comprises subjectlng'a billet to. forging stages in which the billet is compressed so as'to produceflowvof the metal at substantially right angles to the compressive forces, and in a direction to rection of flow intheiirst-named forging stagu; the defamation produced by said intermediate forging stages for the maior partof the deformation produced in the said nrst-namedforging stages, theiinal stage of deformation being eflected bum.

8..Aprocessofforging in which the billetis "W v duce flow of the metal 'ateubstantially right angles to the compressive forces; andin a' direc-' tion to produce de'slredrand ms between said main: stages intermediate "forgingstages in which pressure isapplied to the v deformed billet substantially parallel tov the direction of metal flow in the first-named forging- J mumm alloys in. stag which 's'ubiecting s"; billet w for! M '10 data pimstages,- the deformation produced by'said-intermediate i-forgi'ng stages for the maior part of the deformation produced in the.

sald'flrst-named forging stages. the final-stage of deformation being elected by swaglng at the ormation.

lowest temperature compatible with plastic 4 1- iii l

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