Classifications

• • 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
  • C22C23/02—Alloys based on magnesium with aluminium as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/0408—Light metal alloys
• • 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
  • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
  • C23C4/12—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the method of spraying
  • C23C4/123—Spraying molten metal

Definitions

• the invention relates to an economical process for obtaining a magnesium alloy having mechanical characteristics (breaking strength greater than 290 MPa, the elongation at break generally being at least 5%) and properties relating to improved corrosion, and the alloy obtained by said process.
• the Applicant has specifically sought to use simpler means and thus more economical methods, making it possible to significantly improve the properties, in particular the mechanical characteristics and the corrosion resistance, of the alloys, based on magnesium obtained by conventional casting.
• the applicant has sought to develop an economical process for obtaining a magnesium-based alloy having improved mechanical characteristics, in particular a breaking strength greater than 290 MPa, but particularly of at least 330 MPa, while having an elongation at break of at least 5% and a very good resistance to corrosion.
• This process is characterized in that an ingot with the following weight composition is formed by spraying and depositing in massive form (process generally known by the name of "spray deposition"): Al 2 - 9% Zn 0 - 4% Mn 0 - 1% It 0.5 - 5% TR 0 - 4% (Rare earths) with the following contents of main impurities: Yes ⁇ 0.6% Cu ⁇ 0.2% Fe ⁇ 0.1% Or ⁇ 0.01% the rest being magnesium and that said ingot is subjected to a consolidation treatment by hot deformation between 200 and 350 ° C.
• Another object of the invention is the alloy obtained by the process according to the invention, an alloy characterized by a homogeneous matrix of magnesium whose grain size is between 3 and 25 ⁇ m comprising particles of intermetallic compounds, preferably precipitated with grain boundaries, of the Mg17Al12, Al2Ca, Mg-TR, Al-TR type with dimensions less than 5 ⁇ m. This structure remains unchanged after 24 hours at 350 ° C.
• the alloy always contains calcium and aluminum.
• TR Rare Earths especially Nd, Ce, La, Pr, Misch Metal (MM), but also Y. It is also possible to use a mixture of these elements.
• the process consists in spraying the molten alloy using a neutral gas such as Ar, He or N2 at high pressure in the form of fine liquid droplets which are then directed and agglomerated on a cooled substrate, generally formed by the alloy solid itself, or by any other metal, for example stainless steel, so as to form a massive and coherent deposit, however containing a low closed porosity.
• a neutral gas such as Ar, He or N2
• the ingot obtained can be in the form of billets, tubes, plates, etc., the geometry of which is controlled.
• a technique of this type is generally known as "Spray Deposition".
• This process although using the spraying of a jet of molten alloy with a neutral gas is very different on the one hand from the quenching processes on a roller or on a drum, and on the other hand from the conventional atomization processes.
• the solidification speed is faster than in conventional production processes (for example molding, conventional casting, etc.) where it is much less than 10K / second.
• a massive product is obtained having an equiaxed structure with fine grains.
• the ingot thus obtained is transformed by hot deformation between 200 and 350 ° C, preferably by spinning and / or forging, but also by HIP (Hot Isostatic Pressing). It is remarkable that such alloys can thus be transformed at such high temperatures, reaching 350 ° C., while retaining excellent mechanical characteristics.
• Such thermal stability has many advantages, in particular the possibility of using a high spinning speed, high spinning ratios, while preserving the good mechanical characteristics obtained according to the invention.
• the consolidated ingots can be subjected to heat treatments, either by dissolving followed by quenching and tempering (treatment T6), or directly tempering (treatment T5).
• treatment T6 quenching and tempering
• treatment T5 directly tempering
• the alloys are dissolved by a heat treatment of at least 8 h at 400 ° C. It is followed by quenching with water or oil, then tempering for example 16 h at 200 ° C to obtain maximum hardness.
• the alloys obtained according to the invention have a homogeneous structure preferably having a grain size between 3 and 25 ⁇ m and comprising particles of intermetallic compounds preferably precipitated at the grain boundaries.
• Ca generally precipitates in the form of an intermetallic compound Al2Ca, that is to say a compound between two addition elements, and that even for the lowest Ca contents it is generally only very little present in solid solution in the Mg matrix and is not observed in the form of Mg Ca which is the compound normally expected in an Mg / Ca system.
• alloys based on magnesium having excellent mechanical characteristics significantly higher than those obtained with the alloys of the prior art of conventional casting, and in particular a breaking strength greater than 330 MPa, the addition elements additionally providing better stability. temperature and improved corrosion resistance.
• the weight loss observed with the alloys of the invention after soaking in an aqueous solution at 5% (weight) of NaCl, expressed in mcd (milligrams per cm2 and per day) does not exceed 0.8 mcd whereas for a conventional conventional spinning AZ91, it can reach 2 mcd.
• the corrosion observed is perfectly homogeneous and uniform, and thus avoids the presence of pitting or preferential corrosion zones which can be the cause of preferential rupture zones.
• the process according to the invention is, moreover, more economical, thanks inter alia to a higher productivity, and safer than the processes of quenching on a roller or atomizing because the handling of divided products is eliminated.
• the products obtained do not contain oxides or hydrates capable of creating porosities or inclusions. This results in better metallurgical health which results in an improvement of the tolerance properties for damage (fatigue, toughness, ductility) compared to alloys or conventional or obtained by rapid solidification and / or powder metallurgy.
• the gas flow rate is approximately 3.1 Nm3 / kg and the liquid flow rate is approximately 3 to 4 kg / min. ; they are identical from one test to another.
• the billets obtained are then consolidated by spinning at 300 ° C with a spinning ratio of 20 and a speed of advance of the pestle of 1 mm / sec.
• Table 1 groups together the results obtained: TYS (0.2) represents the elastic limit measured at 0.2% elongation in tension; it is expressed in MPa. UTS represents the breaking load; it is expressed in MPa. e represents the elongation at break and is expressed in%
• Corrosion - the weight loss expressed in mg / cm2 / day (mcd), observed after immersion of the sample in a 5% NaCl solution for 3 days. - the appearance of corrosion.
• TABLE 1 outside invention TEST NO. 1 2 3 4 5 6 7 Composition of the alloy% by weight (1) (AZ91) (AZ91) Al 5 9 8.5 7 7 8.5 8.5 Zn 3 0 0.6 1.5 1.5 0.6 0.6 Mn 0 0 0.2 0 1 0.2 0.2 It 2.5 2.5 2 4.5 4.5 0 0 TR (2) 2.0 2.0 0 1.0 0 0 0 Spinning temperature ° C 300 300 300 300 300 300 300 300 300 300 200 210 TYS (0.2) Mpa 346 381 305 435 381 226 307 UTS MPa 382 423 365 480 422 313 389 e% 22.3 18.0 9.5 5 8.8 15.6 16.5 Corrosion: weight loss mg / cm2 / d 0.25 0.80 0.08 0.25 0.4 0.5
• tests 1 to 5 illustrate the invention, while tests 6 and 7 give results outside the invention.
• Test 6 relates to an alloy of the AZ91 type obtained by conventional casting and spinning, while test 7 relates to the same type of alloy obtained by spray-deposition and spinning. It can be noted that these alloys are close to AZ80 which is the standard wrought alloy (like the alloy ZK60 containing Zr), which is known to give the best mechanical characteristics after spinning, according to the prior art.
• the alloys according to the invention give mechanical characteristics significantly superior to those of the alloys outside the invention, although the spinning took place at a temperature of 300 ° C less favorable than the 200 ° C of tests 6 and 7, for obtaining good mechanical characteristics. Furthermore, it is noted that according to the invention, it is possible simultaneously to reduce the weight loss due to corrosion by a factor of 5 or 6 while having uniform corrosion (test 3), and that the use of TR allows an increase. mechanical characteristics with also uniform corrosion (tests 1, 4).
• the first two alloys are produced according to the invention: they are alloys 3 and 4 in Table 1.
• the third is a conventional AZ80 alloy.
• the fourth has the composition of alloy 3, but was solidified quickly by quenching on a roller, then consolidated by spinning.
• the alloys used according to the invention have: - a breaking load greater than or equal to that of conventional alloys, but less than or equal to that of the alloys obtained by rapid solidification; - a toughness greater than that of the alloys obtained by the two other methods of implementation; - a fatigue limit generally higher, or at least of the same order of magnitude, than that of conventional or rapidly solidified alloys; - a significantly higher endurance ratio than that of conventional or rapidly solidified alloys

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Plasma & Fusion (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Physics & Mathematics (AREA)
• Manufacture Of Metal Powder And Suspensions Thereof (AREA)
• Powder Metallurgy (AREA)
• Extrusion Of Metal (AREA)
• Forging (AREA)
• Coating By Spraying Or Casting (AREA)

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• 1989
  • 1989-08-24 FR FR8911356A patent/FR2651244B1/fr not_active Expired - Fee Related
• 1990
  • 1990-08-21 EP EP90420382A patent/EP0414620B1/de not_active Expired - Lifetime
  • 1990-08-21 DE DE69006293T patent/DE69006293T2/de not_active Expired - Fee Related
  • 1990-08-23 US US07/571,224 patent/US5073207A/en not_active Expired - Fee Related
  • 1990-08-23 CA CA002023900A patent/CA2023900A1/fr not_active Abandoned
  • 1990-08-23 NO NO903711A patent/NO176483C/no unknown
  • 1990-08-24 JP JP2224165A patent/JPH0397824A/ja active Granted

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