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

Definitions

• the present invention relates to claims 1 and 2 of the main French application 88-02885 and relates to magnesium alloys with high mechanical strength and their manufacturing process.
• These alloys have a breaking load at least equal to 290 MPa, but more particularly at least 400 MPa and an elongation at break generally of at least 5% and have, in combination, the following characteristics: - a weight composition located within the following limits: Aluminum 2-11%, preferably 3 to 9% Zinc 0-12%, preferably 0 to 3% Manganese 0-1%, preferably 0.1 to 0.2% Calcium 0.5-7%, preferably 1 to 7% Rare Earth (TR) 0.1-4%, preferably 0.5-2.5% with the following contents of main impurities: Silicon ⁇ 0.6% Copper ⁇ 0.2% Iron ⁇ 0.1% Nickel ⁇ 0.01% the rest being magnesium.
• Mn an average grain size of less than 3 ⁇ m -
• They consist of a homogeneous matrix reinforced by particles of intermetallic compounds precipitated at the grain boundaries Mg17Al12 possibly Al2Ca, depending on the concentration of Ca, Mg32 (Al, Zn) 49, if Zn is present in the alloy, Mg- TR and / or Al-TR, depending on the content and / or the nature of the rare earth, these particles being of an average size less than 2 ⁇ m and preferably less than 0.5 ⁇ m this structure remaining unchanged after 24 hours at 300 ° C.
• Mn is present, it is an element at least quaternary and its minimum weight content is preferably 0.1%.
• alloys also have improved corrosion resistance; in fact, unlike the alloys described in the main French application 88-02885 and its first certificate of addition 89-01913, which exhibit localized corrosions (for example pitting, corrosion according to the machining streaks, etc.) which can cause the along areas of weakness, they exhibit at least as little but also more homogeneous corrosion.
• the alloys according to the invention therefore contain, in the required proportions, both calcium and rare earths, in particular Y (understood here as a TR), Nd, Ce, La, Pr or misch metal (MM).
• the calcium may be in the form of Al2Ca dispersoids precipitated at the grain boundaries and / or in solid solution.
• the particles of the intermetallic compound Al2Ca appear when the Ca concentration is sufficient; they are less than 1 ⁇ m in size and preferably less than 0.5 ⁇ m in size. The presence of Mn is not necessary.
• the TRs the dispersoids appearing from certain concentrations specific to each of the TRs.
• intermetallic particles for example based on Al and Mn, of very small size (of the order of 40 to 50 nanometers) can also be dispersed in the magnesium grains.
• the alloys are obtained by the methods and the various modes of implementation described in the main application which form an integral part of the description.
• the alloy in the liquid state is subjected to rapid solidification, at a speed at least equal to 104K sec ⁇ 1, generally less than 106K sec ⁇ 1, so as to obtain a solidified product, of which at least one of the dimensions is less than 150 ⁇ m, said product then being consolidated directly by precompaction and compacting or by direct compacting, the compacting taking place at a temperature between 200 and 350 ° C.
• the solidified product does not undergo any other conditioning operation such as grinding before being consolidated by precompaction and / or compacting, this operation possibly being of a nature to alter the mechanical characteristics of the consolidated alloy obtained.
• Rapid cooling for solidification can be obtained: - Either by casting in the form of a ribbon on a device called "hyper-quenching on a roll", usually consisting of an energetically cooled drum on which the metal is poured. - either by fusion of an electrode or by jet of liquid metal; the liquid metal is then mechanically divided or atomized and projected onto an energetically cooled surface and kept clear, - Or by atomization of the liquid alloy in a jet of inert gas.
• the first two modes of application make it possible to obtain a solid in the form of ribbons, scales or platelets, while the latter gives powder. These methods are described in detail in the main application and do not form part of the invention as such.
• the rapidly solidified product can be degassed under vacuum at a temperature less than or equal to 350 ° C. before consolidation.
• Consolidation is carried out, according to the invention, directly on the solidified products, in particular directly on the scales or plates.
• Consolidation is essential to avoid long exposures to high temperatures. We chose to operate a warm spinning which minimizes the duration of passage at high temperature.
• the spinning temperature is between 200 and 350 ° C; the spinning ratio is generally between 10 and 40, preferably between 10 and 20, and simultaneously the speed of advance of the pestle is preferably between 0.5 and 3 mm / sec, but it can be higher.
• the solid product before consolidation can be introduced directly into the press container, or after precompaction at a temperature of at most 350 ° C. with introduction into a sheath of Mg or its alloys, or Al or its alloys, itself introduced into said container.
• the process according to the invention makes it possible to unexpectedly obtain a consolidated magnesium alloy which has, as already described, a fine structure (grains less than 3 ⁇ m) reinforced by intermetallic compounds, and high mechanical characteristics remaining unchanged, as well as the structure of said alloy, after prolonged maintenance at a temperature reaching or even exceeding 350 ° C.
• Corrosion resistance is also improved in uniformity and in weight loss (which is reduced).
• tests 20-21-22 which illustrate the present invention, while tests 4-23-7-9-11-12 illustrate the prior art and are drawn in part from the previous application for a certificate of addition FR 89-01913.
• Tests 4 and 23 relate to alloys treated by rapid solidification and consolidation of composition identical to that of AZ91; tests 7-9-11-12 relate to alloys containing Ca also obtained by rapid solidification and consolidation. It will be noted that all of these alloys exhibit corrosion results and / or mechanical characteristics inferior to those of the alloys according to the invention. Samples 23, 4 and 7 undergo heterogeneous corrosion with relatively high weight losses; samples 4 and 7 also have mechanical characteristics much lower than those of the alloys according to the invention. Sample 11 exhibits uniform corrosion but a high loss of weight, comparable to that of alloy 20, and of mechanical characteristics much lower than those of the latter and also those of alloys 21 or 22. Finally, the sample 12 has excellent resistance to corrosion, on the other hand its mechanical characteristics are much lower than those of the alloys according to the invention.
• the invention makes it possible to obtain alloys having improved corrosion resistance (uniform corrosion, generally reduced weight loss) while having increased mechanical characteristics for a high spinning temperature.
• This last advantage is important since such temperatures make it possible to spin profiles of large dimensions and / or to increase the spinning speeds while retaining good mechanical characteristics.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacture Of Metal Powder And Suspensions Thereof (AREA)
• Forging (AREA)
• Powder Metallurgy (AREA)

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Citations (3)

• 1990
  • 1990-08-21 DE DE69007920T patent/DE69007920T2/de not_active Expired - Fee Related
  • 1990-08-21 EP EP90420383A patent/EP0419375B1/de not_active Expired - Lifetime
  • 1990-08-21 JP JP2219876A patent/JPH0390530A/ja active Pending
  • 1990-08-23 US US07/571,226 patent/US5078962A/en not_active Expired - Fee Related
  • 1990-08-23 CA CA002023837A patent/CA2023837C/fr not_active Expired - Fee Related

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