FR2492411A2 - OXIDATION RESISTANT MAGNESIUM ALLOY CONTAINING BERYLLIUM - Google Patents

Abstract

MAGNESIUM ALLOY HAVING GOOD RESISTANCE TO OXIDATION IN MELTED STATE. IT CONSTITUTES ESSENTIALLY, BY WEIGHT, A MAXIMUM OF 12 ALUMINUM, A MAXIMUM 30 OF ZINC, A MAXIMUM 1.5 OF SILICON, A MAXIMUM 0.18 OF MANGANESE AND 0.0025 TO 0.0125 OF BERYLLIUM, THE REMAINING ESSENTIAL FORM OF MAGNESIUM. APPLICATION TO THE REALIZATION OF MOLDED PARTS UNDER PRESSURE, PRACTICALLY FREE OF FLUX INCLUSIONS.

Description

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  The present invention relates to improvements

  made to the subject of the patent application FR 80.08.932.

  In general, the invention relates to alloys of

  gnesium which contain beryllium and are sufficiently resistant

  oxidation in the molten state so that it is not

  need to use flux covers to prevent

  excessive oxidation or combustion of the bath when

  they are exposed to oxygenated atmospheres. Beryl

  lium has the effect of reducing the tendency of molten magnesium alloys to oxidise when exposed to

  oxygenated atmospheres, such as air.

  It is advantageous, at least in several respects, to be able to do without a protective cover of flux

  for molten magnesium alloys. First, the eli-

  melting of flux covers causes a decrease

  significant cost price. In addition, the lack of coverage

  melt means that fudge particles can not be

  not mix with the molten magnesium and then be

  caught in the casting, in the form of inclusions of

  fondant. The absence of flux covers also leads to

  if the magnesium yield increases, given the absence of

  this of inclusions and as a result of magnesium loss melted in

the cover.

  It is known to add beryllium to magnesium-based alloys for different purposes. US patents

  2,380,200, 2,380,201, 2,383,281, 2,461,229 and 3,947,268, and

  if an article by F. L. Burkett titled "Beryllium in Magnesium Die Casting Alloys", published in AFS Transactions,

  volume 62, pages 2 to 4 (1954), describe the addition of

  ryllium to magnesium-based alloys. Among the documents

  mentioned above, US Patents 2,380,200 and

  2.380.201 and Burkett's article indicate that beryl-

  This reduces the tendency of molten magnesium alloys to oxidize. These previous efforts to reduce oxidation do not involve an addition of beryllium at the rates provided according to the present invention and do not appear

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  include the need for a restriction of the content of

  ganesis to allow increased solubility of beryllium in

  the magnesium alloy. In addition, Burkett's article sug-

  even manages to avoid higher levels of beryllium.

  The magnesium alloys according to the invention

  up to 12% aluminum, up to a maximum of

  30% zinc, at most about 1.5% silicon, at most

  about 0.18% manganese, and about 0.0025 to 0.0125%

  of beryllium, the rest being essentially

  sium. All percentages are by weight. It is preferable to limit the manganese content to a maximum of about 0.05% when the beryllium content is about 0.01 to 0.0125%, to increase the solubility of beryllium.

  in molten magnesium to an extent sufficient to

  - put the aforementioned amount of beryllium to dissolve in magnesium. For example, about 0.15% of manganese allows

  the dissolution of about 0.007% of beryllium in magnesium

melted sium.

  It is preferable to maintain the manganese between about 0.04 and 0.15% and the beryllium between about 0.005 and 0.0125% in the magnesium alloys according to the invention to increase the resistance of the alloy to corrosion. It is also preferable to restrict the manganese between approximately 0.08 and 0.15% and the beryllium between approximately 0.006 and 0.01%.

  to further increase the corrosion resistance of

magnesium bindings.

  The principles of the invention can easily be adapted to the manufacture of magnesium alloy die cast parts. Magnesium alloys for die casting can contain from 1 to 12% aluminum, preferably 2 to 12% of aluminum, not more than 30% of zinc, not more than 1,5% of silicon, and 0,2 to 1,0% of manganese,

  the remainder being essentially magnesium.

  The zinc content of magnesium alloys has

  has been limited to a maximum of 1.5% zinc. Zinc, in magnesium alloys, at contents ranging from 2492411 * i

  up to 1.5%, improves the mechanical properties and

  resistance to corrosion of alloys while maintaining

  very good casting properties.

  Alloys with a zinc content greater than 1.5%

  There is a marked increase in hot breaking or cracking during casting. In fact, the molding of magnesium alloys presents problems when the zinc content is greater than 1.5% and less than 12%. This is due to

  the widening of the solidification temperature range.

  These problems have been limited by adjusting the levels of

  zinc and zinc present in the magnesium alloy. the

  contrary, when the zinc content in a metal alloy

  gnesium is between 12 and 30%, the alloys

  feel properties of moldings superior to those of

  alloys containing 1.5% to 12% zinc.

  Magnesium alloys with zinc contents

  greater than 1.5% have advantages and disadvantages

  vantages. The advantages of these alloys include the

  lower melting points and greater fluidity. These

  advantages are combined, depending on the zinc content, to

  to be molded at a temperature of 32 to 1220C lower than that generally used for the molding of low-zinc magnesium alloys, while maintaining a

  good fluidity. The low melting point also increases the

  resistance to oxidation of magnesium alloys during molding. However, alloys with a high zinc content may have problems with moldability,

  density, ductility and higher costs.

  The higher the zinc content in the alloys

  In magnesium, the greater the density, the cost and the fragility. The problems of high zinc alloys are offset by the benefits of using them for certain applications. Accordingly, the recommendation of a high zinc content appropriate for

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  a given use must be made carefully

  The manganese content of the alloys according to the invention

  tion is important because of its influence on the solubility

  the ease of alloying beryllium with magnesium

  of. Proof that this influence was not recognized

  previously, the AZ9lB alloy, which is an alloy of

  widely used pressure alloy, whose composition

  nium contains 9% aluminum, 0.7% zinc, 0.2% manganese

  A maximum of 0.5% of silicon, a maximum of 0.3% of copper and a maximum of 0.03% of nickel, the remainder consisting essentially of magnesium, contains less than 0.001% of beryllium. It has been found that beryllium is soluble in AZ91B magnesium alloys to a greater extent than previously believed. In any case, a rate of beryllium

  in the order of 0.001% is considered insufficient to

  to have a good protection of molten magnesium. On the contrary, it has been determined that approximately 0.0025 to 0.015% of

  of beryllium in molten magnesium or its alloys for

  hiber the combustion, the amount of beryllium being increased to

  as the oxygen content of the atmosphere increases.

  As a result, the manganese content should not exceed about 0.18% and preferably it should not exceed about 0.15%. In the case of nitrogen atmospheres and short exposure times, additions of approximately 0.0025 to

  0.005% of beryllium is sufficient to ensure the protection of the

  molten gnesium. On the other hand, when the exposure times are longer, or when there is a significant air infiltration in the nitrogen atmosphere, the beryllium contents of the order of 0.005 to 0.01% are recommended. . On the other hand, if it is desired to inhibit the combustion of molten magnesium or

  molten magnesium alloys staying in the air, a

  Beryllium neur from about 0.011 to 0.0125% is preferable.

  Such levels of beryllium make it necessary to limit the amount of

is about 0.05% maximum.

  The amount of beryllium used depends on the amount of oxygen in the atmosphere above the bath. By

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  example, if molten magnesium is exposed to air without

  the oxygen content of the atmosphere will remain at around 20% and, as a result,

  beryllium, in the order of 0.01 to 0.015%, to avoid oxidation

  excessive combustion or combustion. If molten magnesium is exposed for prolonged periods, it may be desirable

  to periodically add beryllium to compensate for the oxidation

  for example, 0.02%, so that the proportion exceeding the solubility limit gradually dissolves

  to compensate for oxidation losses and maintain / e-

  ryllium at or near the saturation level,

in molten magnesium.

  To reduce the proportion of beryllium required

  For good bath protection, it is desirable to keep the oxygen level as low as possible. It is

  useful, from this point of view, to put a lid or a hot-

  over the molten magnesium. The reaction of the molten metal

  oxygen, in enclosed air, decreases the

  gene of the atmosphere. If the system is very tight and if the resulting oxygen content becomes very low,

  only 0.0025% of beryllium provide sufficient protection

  cient. If the system is not waterproof, or if it is opened periodically for short periods of time for operations

  such as bag sampling, it is sometimes desirable

  to introduce enough nitrogen or other inert gases

  to keep the oxygen levels low. In these

  conditions, an intermediate level of beryl can be used.

  lium, for example 0.005 to 0.01%. It is also possible to use

  very protective gases, such as SF2, SO2 and various inert gases.

  although nitrogen is preferable because it is related to

accessible.

  Impurities such as iron tend to form

  with the beryllium of the intermetallic compounds and, in

  sequence, they must be kept to a minimum. Since manganese, in the presence of aluminum contents of

  the order of 1 to 12%, forms with iron a relative phase

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  insoluble material which is then deposited at the bottom of the bath, it may be included in the alloys for casting under pressure, in order to

  purification, small amounts of manganese, for ex-

  0.1% example. However, the manganese content should not be high enough to precipitate beryllium. In practice, it is necessary to lower the manganese content from 0.18% to 0.05% as

  the beryllium level increases from 0.0025% to 0.015% in the

  magnesium binders containing about 9% aluminum.

  The experimental results below illustrate

  some of the principles on which the invention is based.

  A hood was kept under a hood for 8 hours.

  test magnesium alloy containing about 9% aluminum

  nium, about 0.7% zinc and about 0.0025% beryllium,

  without the occurrence of combustion or excessive oxidation

ves.

  A load of 59 kg of an alloy containing

  7.1% of aluminum, 0.71% of zinc, 0.05% of manganese,

  the remainder being magnesium, it has been covered with a

  and kept under a hood at 6770C. Once the flux was removed by skimming, the burning of the molten alloy occurred after one minute. It was then extinguished by establishing a fondant blanket. We have

  closed the hood, and nitrogen was

  the melted bath covered with flux, at a flow rate of 0.85 m3 / h for about 5 minutes. The hood was closed, the flux cover removed and nitrogen continued to flow at 0.85 m3 / hr. After 30

  minutes, he began to form magnifiers (local areas).

  strong oxidation) which increased in size. the

  After 51 minutes, the loupes began to burn slowly.

  and emitted a bright light. We then opened

  periodically the hatch of the hood for a short time to

  able to take samples from the pocket and sink

  test tubes in bar. The combustion became more vigorous after 5 minutes of casting and very intense after

minutes.

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  Additional tests were carried out in addition to

  so many amounts of beryllium to the molten magnesium test alloy described in the preceding paragraph. In general,

  the tests indicated that additions of beryllium

  hinder the burning tendency of the molten alloy. Lors-

  about 0.008% of beryllium has been incorporated, we have now

  the alloy satisfactorily under a flow of nitrogen

  of 0.85 m3 / h, then test bars were cast.

  This alloy was also maintained in the air, without

  for about 15 minutes. As we increase

  During the various tests, it was found that the oxidation resistance of the molten magnesium alloy increased and that lower nitrogen rates were required for satisfactory operation. When incorporated into the molten alloy about 0.011 to 01013% of

  beryllium, the surface of the alloy has

  kept it exposed to air under conditions of

  satisfactory, then poured under pressure. Lors-

  deliberately puncturing the superficial silver film

  the protector, a new film was formed instantly, indicating that the protective function of beryllium was still occurring. However, after about 1 hour of exposure to the air, it began to form

  oxide magnets that were slowly developing.

  When 0.0025% of beryllium was incorporated into

  test magnesium binding, the bath was maintained so

  satisfactory under a nitrogen flow of 0.85 m3 / h, the trap-

  pe being closed and then cast test bars bar. After 15 minutes, the molten magnesium alloy formed many magnifying glasses and began to burn. when

  incorporated 0.007 to 0.01% of beryllium, the casting

  successfully killed, without formation of magnifying glasses, with 1.7 m3 / h of nitrogen. The hatch of the hood was then kept open

  for 15 minutes, without forming loupes. We have

  when stopped the stream of nitrogen and the alloy was maintained

  melted for another 15 minutes, without forming magnifying glasses.

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  Once the alloy of about 120 to 130 ppm of beryllium had been saturated at 649 to 704% C, it was kept in the open air for more than 30 minutes without

  that it is formed of magnifying glasses, then it was sunk with success -

  without nitrogen atmosphere. However, an extended stay

  finally gave up the formation of magnifying glasses.

  To determine the compatibility of manganese and beryllium in magnesium alloys, two ingots of AZ91B alloy containing about 0.2% manganese were added to the bath. This addition reduced the beryllium content

  at about 0.008% and had the 0.12% manganese content.

  The molten alloy was then cast under pressure with a

  nitrogen flow rate of 1.7 m3 / h and the trap door was opened.

  only when it was necessary. We sank in the air

  a portion of the bath in a large mold. There was no mention

  a discoloration of the surface of the metal while-

he was solidifying himself.

  To the molten alloy was added another ingot of

  AZ9lB, which had the effect of reducing the

  beryllium to about 0.007% and to bring the manganese

  about 0.15%. Again samples were cast

  bar under a stream of nitrogen of 1.7 m 1h. At the end of the

  During this time, several loupes were formed.

  Variations in manganese and beryl

  lium had no apparent effect on the flowability of

  the magnesium alloy test. It seems that an increase

  the beryllium content causes some improvement

  the fluidity and appearance of the surface,

  because of less oxidation of the melt.

  Five tensile tests were

  bar to determine the effect of beryllium and man-

  ganèse. The results shown in Table I show that

  lower maganese content and higher beryl content

  lium have the effect of increasing both ductility and

  the tensile strength of the magnesium alloy of

nos,

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  We also dive for 3 days in salt water

  (3% NaCl) sandblasted bar samples from each

  bonding, to determine the corrosion resistance. We have

  Sandblasted bars to remove cast surface. The results

  Table II states that additions of beryl-

  reduce the rate of corrosion of the alloy of

  gnesium test by salt water, bringing it to the same value

  reduced than that obtained by additions of mana-

  ganese. Small amounts of manganese, for example 0.12%, reduce the amount of beryllium required for good corrosion resistance. The improvement ensured by the

  beryllium can be attributed to a decrease in

iron neur.

TABLE I

  % Be% Mn Elastic limit elongation-% tensile loading in tensile * tension *

0 0.05 6 1512 2552

0.0025 0.05 7 1610 2735

0.0086 0.05 6 1596 2587

0.0113 0.04 7 1476 2686

0.0125 0.04 5 1547 2658

0.0081 0.12 6 1596 2742

0.0071 0.15 8 1540 2847

0.0006 ** 0.2 4 1526 2433

* kg / cm2 ** (AZ9lB)

TABLE II

% Be% Mn% Fe Speed of corro-

if we *

- '0.05> 0.15 3.30

0.0025 0.05 0.15 2.41

0.0086 0.05 0.008 0.43

0.0113 0.04 0.005 0.08

0.0125 0.04 0.005 0.08

0.0081 0., 12 0.006 0.08

0.0071 0.15 0.007 0.08

0.0006 ** 0.2 0.003 0.08

* cm / year

** (AZ91B)

Claims (11)

  1. Magnesium alloy with good resistance   melt oxidation, good corrosion resistance, good ductility and good tensile strength, said alloy containing aluminum, zinc, silicon, manganese, and beryllium, characterized in that   it consists essentially of 2 to 12% aluminum, at most   30% zinc, at most 1.5% silicon, 0.04 to 0.15% manganese, 0.005 to 0.0125% beryllium, the balance being   essentially consisting of magnesium.   2. Magnesium alloy according to claim 1,   characterized in that it contains from 0.005 to 0.01% beryl epithelium.   3. Alloy according to one of claims 1 or 2,   characterized in that it contains 0.08 to 0.15% of manganese and from 0.006 to 0.01% beryllium.   4. Alloy according to any one of the claims   1 to 3, characterized in that it contains about 9% of   luminium, about 0.7% zinc, about 0.12% manganese and about 0.008% beryllium.   5. An alloy according to claim 1, characterized in that it contains at most 0.05% manganese and 0.011 at 0.0125% beryllium.   6. Alloy according to claim 1, characterized in that it comprises at most 1.5% of zinc, at most   0.05% manganese and 0.011 to 0.0125% beryllium.   7. Die castings, characterized in   what they are practically free from fungi inclusions   having good corrosion resistance, good   ductility and good tensile strength, which is   are formed of an alloy according to one of   any of claims 1 to 5.   8. A method of manufacturing magnesium alloy parts molded under pressure, characterized in that melting an alloy according to claim 1, the bath being exposed to an oxygenated atmosphere, and which is cast under   pressure the molten alloy to obtain a practically molded he 12 2492411   free of flux inclusions.   9. Process according to claim 8, characterized   in that the bath is exposed to an atmosphere containing a   higher proportion of nitrogen than air.   10. Process according to claim 8, characterized in that an alloy according to claim 2 is used. 11. Process according to claim 8, characterized   in that the alloy contains about 0.01 to 0.015% of beryl   lium and at most 0.05% of manganese and in that the bath is exposed to the air.