Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/40—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using liquids, e.g. salt baths, liquid suspensions
  • C23C8/42—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using liquids, e.g. salt baths, liquid suspensions only one element being applied
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C23/00—Alloys based on magnesium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C23/00—Alloys based on magnesium
  • C22C23/04—Alloys based on magnesium with zinc or cadmium as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C23/00—Alloys based on magnesium
  • C22C23/06—Alloys based on magnesium with a rare earth metal as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C24/00—Alloys based on an alkali or an alkaline earth metal
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C25/00—Alloys based on beryllium
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
  • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied

Definitions

• This invention relates to magnesium base alloys containing at least 80 percent magnesium. It is a common experience in magnesium base alloys that a grain boundary phase may have an embrittling or other deleterious effect on the alloy and the object of the present invention is to reduce this harmful effect.
• the addition of rare earth metals to magnesium results, when the rare earth metal exceeds a certain percentage, in a brittle grain boundary phase. Providing that the addition of rare earth metal does not exceed a known percentage, the grain boundary phase may be taken into solution by heat treatment in known manner and the embrittling effect is thus reduced. If the amount of rare earth metals exceeds the limit of solid solubility, however, complete solution of the phase by heat treatment in known manner is impossible. Further, it is known that if the magnesium base alloy also contains zinc, the grain boundary phase resulting from addition of rare earth metal is very stable and cannot be dissolved by heat treatment in known manner.
• a magnesium alloy is provided with an alloying constituent consisting of at least one of the elements rare earth metals and thorium, some at least of which is incorporated in a grain boundary phase, and the alloy is then heated in the presence of hydrogen to effect reaction of hydrogen with said constituent and to cause part at least of the grain boundary phase to diffuse into the base metal.
• rare earth metals for the purpose of the I present invention includes yttrium.
• the alloying element which is to react with hydrogen may be termed the active constituent.
• the hydrogen may, for example, react with the active constituent in the grain boundaries to form hydride thus attacking the grain boundary phase and liberating one or more of its constituents to go into solution in the mag nesium. Or, for further example, the hydrogen may react with the active element already dissolved in the alpha phase, permitting solution from the grain boundary phase with further progressive attack on the dissolved active constituent.
• a particular application of the invention is in magnesium base alloys containing zinc.
• a magnesium base alloy having high room temperature strength contains zinc 6% and zirconium 0.6 to 0.9%.
• This alloy has a marked tendency to exhibit microporosity in the cast form, such porosity resulting in considerable reduction of strength. This tendency to exhibit microporosity has restricted commercial exploitation of the alloy.
• the tendency to microporosity of this alloy may be improved by addition of rare earth metals, e.g., such as cerium mischmetal or 3,334,998 Patented Aug. 8, 1967 didymium mischmetal which are two forms of commercially available rare earth metal.
• one or more rare earth metals may be included in the alloy and the alloy is then heat treated in the presence of hydrogen so that the hydrogen reacts with one or more of the rare earth metals.
• the improvement in mechanical properties resulting from application of this novel principle is associated with the modification of a metallurgical phase present in the grain boundaries of the alloy.
• the presence of this phase is both responsible for the improvement in respect of microporosity and also the resultant loss in tensile properties.
• the phase is normally very stable and cannot readily be dissolved by heat treatment in previously known manner. It is believed that the introduction of hydrogen during heat treatment converts the rare metal content to hydride, resulting in breakdown of the original phase and thus removing the deleterious eifect on strength. The probability of an improvement in strength when using any given active constituent can, therefore, be assessed by comparative metallographic examination of specimens heat treated in previously known manner with those heat treated according to the present application.
• the present invention therefore, includes a magnesium base alloy consisting apart from impurities of:
• alloys containing both zirconium and manganese if either is at least 0.3% the other will not exceed 0.2%.
• the silicon content will be less than 0.05%
• the RE and zinc contents may be restricted to the following ranges:
• thorium used as an active alloying element it is known that the grain boundary phase formed, particularly when zinc is also present, has a lower embrittling effect than in the case of rare earth metals although for many applications the embrittling effect is too severe. It may therefore be advantageous to use thorium wholly or partly to replace rare earth metals as the active constituent particularly where only partial conversion of the grain boundary is desired.
• the thorium content may be 0.5-2.5 and the RE content 0.75-2.5%. If desired rare earth metals may be used in which the lanthanum content has been diminished, e.g. didymium.
• magnesium alloys for use at elevated temperatures may contain rare earth metals or thorium as an essential alloying addition. Alloys of this type when heat treated in the manner described herein may suffer a loss of high temperature strength owing to conversion of the essential alloying addition to a form unsuitable for the development of high temperature strength.
• the conversion of the active element may be halted before completion, e.g. by suitable choice of time and temperature, leaving the remainder of the active element to perform its other function of providing high temperature strength. In this manner alloys of improved castability and room temperature strength but still retaining high temperature strength may be produced.
• a further advantage relates to alloys having high damping capacity. It is known that a binary alloy of magnesium with nominally 0.6% zirconium has a high damping capacity, and this alloy is used commercially for this purpose. This alloy, however, has very poor casting characteristics and its commercial use for high damping purposes is limited by the inability to cast complex shapes.
• pure magnesium and magnesium alloys containing manganese are known to have high damping capacity but are not used in practice owing to the inability to cast complex shapes.
• the castability of such alloys may also be improved by addition of the active constituents herein listed but such additions in turn reduce the damping capacity.
• the damping capacity of magnesium alloys containing active elements may be improved by heat treatment in hydrogen.
• Preferred compositions afiording good damping capacity combined with good castability are as follows:
• the RE content is preferably 0.25-3%, with zinc 3.5-8% and manganese 0.15-2.5%, the silver being in the range 0- 0.25%, or 0.25-5% where improved properties are desired.
• the temperature of heat treatment of the magnesium alloy may be from C. to the immediate neighborhood of the solidus. Temperatures of at least 450 C. will normally be used for the hydriding step and this will normally be followed by a precipitation treatment at a temperature not exceeding 250 C.
• the hydrogen content of the magnesium alloy will be at least 50 ccs. per 100 grams of the alloy and may be at least 80 ccs.
• the heat treatment may be carried out in an atmosphere of hydrogen or one rich in hydrogen, e.g. ammonia, hydrocarbon gases, etc., and also in an atmosphere containing moisture such that the magnesium alloy reduces the moisture to liberate hydrogen.
• the heat treatment may also be carried out in any other medium, e.g. a salt bath, providing that this is suited to the heat treatment of magnesiumbase alloys, e.g.
• nitrate baths are usually considered unsuitable owing to the risk of explosive reaction between magnesimum and molten nitrates, but chloride baths could be used without such risk; and providing that hydrogen is made accessible to the magnesium alloy, e.g. by addition to the bath of hydroxides or unstable hydrides such as sodium hydride.
• the access of hydrogen in such a heat treatment may also be by an electrolytic process.
• the rate of absorption of hydrogen would increase if the pressure of the hydrogen-containing medium surrounding the magnesium was increased. It would further be expected that partial or complete ionisation of the hydrogen containing medium would increase the rate of hydrogen absorption. This is in accordance with the known principles of gas absorption. It has further been found that the magnesium alloy surface. may be beneficially treated to increase the rate of hydrogen absorption. Such treatments include shot blasting, providing a chromate film on the magnesium alloy surface, and applying salt solution to the magnesium alloy surface.
• magnesium alloy articles in which specific mechanical properties are developed in selected parts of the article, the other parts having specific properties of a different nature.
• a cast article could be made in a magnesium-base alloy containing nominally 3% rare earth metals, 3% zinc and 0.6% zirconium.
• This alloy has good strength at elevated temperatures and has very good castability but has a somewhat low ductility, of the order of 5% elongation in a tensile test.
• the ductility can be increased to a value of about 15% elongation, although in this specific alloy the new principle of treatment would be expected to result in some loss of high temperature strength.
• the hydriding treatment can be restricted to the unmasked areas, providing a cast article with good creep resistance in selected parts and good ductility in other selected parts.
• the rate of progress of conversion of the active element may be controlled to provide modified properties to a restricted depth below the surface of the article being treated.
• the invention can, therefore, be utilised to produce magnesium-base articles having strength characteristics significantly different at their surfaces compared with the characteristics towards the centre of their cross section.
• the invention enables castings to be produced possessing a minimum 0.1% proof stress of 9.0 t.s.i. combined with a minimum elongation value of at least 7%, these figures relating to specimens cut from the casting.
• a magnesium base alloy comprising apart from impurities RE metals percent by weight 0.2-6 Zinc do 0.25-10 Hydrogen ccs./ g. of alloy At least 50 Magnesium Balance 2.
• the alloy of claim 1 including a maximum of approximately 1 percent by weight of zirconium.
• the alloy of claim 1 including a maximum of approximately 2.5 weight percent manganese.
• the alloy of claim 1 including a maximum of approximately 1 percent by weight zirconium and about 2.5 percent by weight manganese, the zirconium and manganese being so related that if either is at least 0.3 percent the other will not exceed 0.2 percent.
• a magnesium base alloy comprising the following composition:
• a magnesium .base alloy having the following composition:
• a magnesium base alloy having the following composition:
• a magnesium 'base alloy having the following composition:

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• Chemical Kinetics & Catalysis (AREA)
• Manufacture And Refinement Of Metals (AREA)
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• Electrolytic Production Of Metals (AREA)
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• Hard Magnetic Materials (AREA)

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Citations (4)

• 1963
  • 1963-11-15 GB GB55204/65A patent/GB1075010A/en not_active Expired
  • 1963-11-15 GB GB45142/63A patent/GB1035260A/en not_active Expired
• 1964
  • 1964-11-06 US US409584A patent/US3334998A/en not_active Expired - Lifetime
  • 1964-11-11 NL NL646413107A patent/NL143280B/nl not_active IP Right Cessation
  • 1964-11-13 DE DEM63117A patent/DE1248306B/de active Pending
  • 1964-11-13 SE SE13696/64A patent/SE307677B/xx unknown
  • 1964-11-13 CH CH1468364A patent/CH436734A/fr unknown
  • 1964-11-13 BE BE655735A patent/BE655735A/xx unknown

Patent Citations (4)

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