US2029728A - Rolling magnesium alloys - Google Patents

Description

Patented Feb. '4, i936 PATENT OFFICE 2,029,728 ROLLING MAGNESIUM annoys Robert D. Lowry and Fred L. Reynolds, Midland.

MIOIL, assignors to The Dow Chemical Com- .pany, Midland, Mich, a. corporation of Michlgan N Drawing. Application February 12, 1934, Serial No. 710,887

4 Claims.

The invention relates to improvements in methods of rolling magnesium base alloys, particularly those which contain relatively small amounts of such alloying metals as aluminum,

5 manganese, cadmium, tin, zinc, etc., and not less than about 85 or 90 per cent of magnesium.

Typical magnesium base alloys suitable for rolling with which our invention may be practiced are those, for example, containing from about 0.5

1.0 to 8 per cent of aluminum and from about 0.1 to 1.5 per cent of manganese, the balance being magnesium. Such magnesium base alloys are among the strongest of those commercially available that possess good resistance to corrosion.

Use of these alloys in commercially available rolled form to make metal articles requiring forming operations, such as bending, drawing. and the like, has been hampered due to the necessity to heat such metal to elevated temperatures to permit making relatively sharp bends or deep draws without fracture.

It is accordingly one of the objects of our invention to produce from magnesium base alloys rolled sheet, plate, profiled shapes, or like products, which possess a degree of ductility permitting the same to be bent, cupped or otherwise worked readily at ordinary temperatures without fracture. We employ the term ductility to designate that quality of the rolled metal by virtue of which such changes in shape may be made at room temperature without fracture. In obtaining numerical values for the ductility we employ a standard Olsen ductility testing machine in which the ball point is 0.875 inch diameter and the circular hole is 1.625 inch diameter. The depth of cup produced by cupping a specimen of the rolled metal without fracture with this machine, isgiven herein as the measure of ductility.

1 We have found that the minimum radius of a 90 bend which may be produced at roomtemperature without fracture also gives a convenient measure of the ductility. In employing this test the radius is expressed in terms of' the thickness of the specimen.

In our Patent No. 1.94l,608, we have disclosed a method for producing ductile magnesium base alloy products by rolling an ingot of the alloy at a temperature from about 800 down .to' 500 or 400 F., annealing therolled metal, and then producing a relatively small further reduction in thickness at a temperature between 40 and 350 F., followed by reannealing. This procedure,

however, has the disadvantage that the relatively small cumulative reduction to final thickness which is carried out when the metal is at a relatively low temperature and therefore hard, requires very heavy rolling pressures and numerous passes each producing only a very slight reduction. The procedure is, therefore, time-consunm ing and adds very materially to the cost of rolling.

Instead of reducing the metal to the ultimate thickness by costly and time-consuming relatively hard rolling at low temperature we have discovered that we may roll the metal to the ultimate thickness while heated to conventional hot roll- 10 ing temperatures, i. e. from about 800 down to 500 or 400 F., and still obtain a ductile product, if after such rolling, the metal is annealed and then subjected to an alternate bending and straightening operation, which repeatedly stresses 15 i the same without substantially altering its thickness, followed by reannealing. This procedure has the advantage that a relatively rapid and inexpensive bending and straightening operation replaces the more costly and time-consuming hard rolling operation, thus materially reducing the cost and time of producing ductile magnesium and magnesium alloy rolled products. The invention, then, consists in the combination of steps hereinafter fully described and particularly 2v pointed outin the claims. 7

In carrying out our invention the metal is-first rolled to the desired thickness by any suitable procedure known to the art. For example, the rolling may be carried out at a temperature between about 800" and 500 or 400 F., so as to produce a reduction in thickness at each pass of 5 to 10 per cent, or whatever the metal will stand without fracture, the-metalbeing reheated from time to time between passes, if necessary.

- The rolled metal is then annealed at a temperature between about 500 and 800 or 900 F. for from one-quarter to two hours or more. At the lower temperatures of the annealing range, a longer time is required than at the higher term 4 peratures. We have found that a suflicient amount of annealing is produced .n approximately one-half hour when the'temperature is maintained between about 700 and 750 F. V Following such rolling and annealing steps, we proceed to stress the metal by alternatebending and straightening, or like stressing operation. without substantially changing its thickness. The radius of curvature or bend which maybe produced in this treatment without fracture 09 depends upon the ductility of the annealed rolled metal. This is usually sullicient to permit bend- I ing about a radius of from '7 to 10 times the thickrepeat such bending followed by straightening several times. A convenient procedure for alternately bending or straightening the metal in this manner consists in passing the same between conventional leveling rolls. Conventional level-- ing rolls in general consist of .two'grcups of five or more power driven rolls. Each group of rolls lies in a plane and the rolls in one plane are in staggered spaced relation to the rolls in the other. The plane of one group of rolls is set at an angle tothe other so that the metal being passed between the groups of rolls is alternately bent in opposite directions with a progressively decreasing curvature until it finally emerges substantially'fiat and straight. It is preferable to carry out such stressing operation at room temperature (50-75 F.), although any temperaturebetween 40 and 275 F. may be used, since at such temperatures no consequential change in the thickness of the metal is produced by the treatment. I

The stressed metal ls'then given a final annealing, which may preferably be done by maintainingit at a temperature between about 500 1 and 800?- or 900 F. for from one half to two hours or more, although annealing for about one hour-at 600 to. 700 F. is usually sufficient.

' The following-examples are illustrative of suitable modes of carrying out the invention.

n Example 1 Amagnesiumbase alloy consisting of 4 per cent of aluminum, 0.3 per cent of manganese, and the balance'magnesium, was cast into an ingot and then e'xtruded to form a rolling slab. The slab was'rolled-into sheet 0.156 inch thick, at a temerature= between about 780 and 400 F. -in a number of passes each producing up to about 10 per cent reduction in thickness, according to the usual procedure. The sheet. was then annealed ity and a minimum radius of bend at room temfor one-half hour at 700 F. At this stage speci-.

mens of the sheet showed 0.089 inch Olsen ductilperature of about 6 times the thickness. The an- "nealed' sheet was given 4 passes between leveling rolls at room temperature and then reannealed at 700 F. for one-half'hour. The annealed sheet showed 0.180 inch Olsen ductility and a minimum radius'of bend of about times the thickness.

Earring 7E2" I A similar extruded rolling slab of an alloy,

' consisting of 96 per cent magnesium and 4 per cent of aluminum, was rolled into sheet 0.156 inch thick, at a temperature between 780 and 400 F. in a numberof passes each producing about 10 per cent reduction in thickness. The

sheet was then annealed for one-half hour-at 700 F. At this stage the sheet showed 0.122 inch Olsen ductility and a minimum radius of bend of 7 times the thickness. The annealed sheet was then given 4 passes between leveling rolls at room temperature and reannealed at 700 F. for onehalf hour. The annealed sheet showed 0.162

inch Olsen ductility and a minimum radius of bend of 2.6 times the thickness of the sheet.

Example 3 A similar extruded rolling slab of an alloy consisting of 94.5 per cent of magnesium, 4 per cent of cadmium, 1 per cent of zinc, and 0.5 per cent of manganese was rolled into sheet 0.130 inch thick at a .temperature between 780 and. 400 F. and then annealed at 700 F. for one-half hour. At this stage the minimum radius of bend. was 5.7 times the thickness. After 4 passes between leveling rolls at room temperature, followed by reannealin-g at 700 F. for one-half hour, the minimum radius of bend, was 4.4 times the thickness.

Although generally it is preferable to anneal the rolled metal prior to stressing the same, as described, we may, in some instances, omitsuch anneal if the metal be rolled at a temperature above about 600 F., since such hot rolling has the effect of annealing. This procedure may be used upon ordinary rolled magnesium base alloyprodnets to improve their ductility. For example, to convert a magnesium base alloy product, already rolled in conventional manner, into a ductile product, it may be rolled again at a temperature between 600 and 850 F. in 1 or 2 or more passes, producing a relatively small further reduction in thickness amounting to aboutlO per cent. The metal, after being cooled, is then stressed by subjecting to alternate bending and straightening and finally reannealing, as already described.

cedure Example 4 An extruded rolling slab similar to those used in previous examples, of an alloy consisting of 4 per cent of aluminum, 0.3 per cent of manganese. and the balance magnesium, was rolled into sheet 0.156 inch thick in conventional manner, 1. e. between 750 and 400 F. This sheet showed 0.075 inch Olsen ductility and a minimum radius of bend of 8 times the thickness. The thickness was then reduced about 10 per cent by rolling at a temperature approximating 700 F. and then subjected at room temperature to stressing by passing between leveling rolls. The sheet was then annealed for one-half hour at about 700 F. Such sheet showed 0.175 inch Olsen ductility and a minimum radius of bend of 2.5 times the thickness.

The use of conventional methods of rolling and annealing to bring the metal to the desired thickness and suitable condition for stressing andan- .nealin'g is illustrated in' Examples 1, 2, and 3.

Therein the rolling was carried out at a temperature between 780 and 400 F. in conventional manner, and the metal was annealed. Thereupon it was subjected to our novel step of stressing at ordinary or moder'ately'elevated temperatures (i. e. 40-275 F.) without substantially reducing the thickness, such stressing being produced by passing the sheet between the rolls of a conventional sheet leveling machine, after which the metal was again annealed. The ductility of the sheet was greatly improved in all cases as shown by the .values obtained. Similar improvement over conventional practice is shown in Example 4 which difiers from the preceding examples in that a relatively small amount of hot rolling (above 600 F.) is substituted for annealing prior to stressing the metal.

Other modes of applying the principle 01' our invention may be employed instead of the one explained, change being made as regards the The following example is illustrative of this promethod and the steps herein disclosed, provided those stated by any of the following claims or their equivalent be employed.

-We therefore particularly point out and distinctly claim as our invention:-

1; In a method of producing a ductile rolled product from a magnesium base alloy, the steps which consist in rolling the metal at a temperature between 800 and 400 F. so as to produce a reduction in thickness, annealing the metal at a temperature between 600 and 850 F., alternately bending and straightening the rolled metal at a temperature between 40 and 275 F. so as to stress the metal without substantially changing its thickness, and annealing the same.

2. In a method of producing a ductile'rolled product from a magnesium base alloy, the steps which consistin rolling the metal. at a temperature between 800 and 400 F. so as to produce a reduction in thickness, then further rolling the metal at a temperature between 600 and 850 F. so as to produce a further reduction in thickness, alternately bending and straightening the rolled metal at a temperature between 40 and v 275 F. so as to stress the metal substantially without changing its thickness, and annealing the same at a temperature between 600 and 800 F.- v

3. In a method of improving the ductility of a relatively non-ductile annealed rolled magnesium base alloy product, the steps which consist in alternately bending and straightening the'product at a temperature between 40 and 275 F., so as to stress the metal without substantially changing its thickness, and thereafter annealing the same.

4. In a method of improving the ductility of a relatively non-ductile rolled magnesium base alloy product, the steps which-consist in annealing the product at a temperature above 600 F., alter- F., so as to stress the metal without substantially changing its thickness, and thereafter annealing the-same.

ROBERT D. LOWRY. FRED L. REYNOLDS.