Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C45/00—Amorphous alloys
  • C22C45/005—Amorphous alloys with Mg as the 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
  • C22C23/02—Alloys based on magnesium with aluminium as the next major constituent

Definitions

• the present invention relates to magnesium alloys with high mechanical strength containing strontium and their manufacturing process. It relates in particular to the commercial magnesium alloys listed under the names AZ 31, AZ 61, AZ 80 (wrought alloys) and AZ 91, AZ 92 (casting alloys), according to the ASTM standard (or alternatively G-A3Z1, G-A6Z1, G-A8Z, G-A9Z1, G-A9Z2 according to French standard NFA 02-004) to which strontium has been added. These alloys can contain manganese and / or calcium as addition elements.
• the rare earths must be refined to contain very little Fe, Ni or Cu, which significantly increases their price. They are also difficult to introduce into the liquid magnesium bath because of their high reactivity with oxygen. Due to their high density, it is more difficult to obtain good homogeneity of the bath during their introduction.
• This alloy may also contain, as an addition, at least one of the elements Zn and / or Ca in the following proportions:
• the matrix consists of fine magnesium grains with an average size of less than 3 ⁇ m or more advantageously not exceeding approximately 1 ⁇ m; it is reinforced by precipitates of intermetallic compounds dispersed homogeneously, preferably at the grain boundaries, of variable size and nature depending on the chemical composition of the alloy.
• Al4Sr, Mg2Sr, Mg17Sr2 and / or Mg17Al12 are preferably found in the grains for sizes less than 0.1 ⁇ m and at grain boundaries for larger sizes between 0.1 and 1 ⁇ m; this is the case for the Mg17Al12 compounds.
• Sr can also be found in solid solution in Mg and Mg17Al12.
• Ca is present in sufficient quantity in the alloy, it is found in solid solution in Mg17Al12 and in the form of fine metastable globules rich in Al and Ca of size less than 0.1 ⁇ m, dispersed in the matrix of Mg and possibly transform into Al2Ca by heat treatment.
• the alloy according to the invention is usually obtained by the rapid solidification processes and the various modes of implementation, described in application EP 89-903172, 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 107K sec ⁇ 1, so as to obtain a solidified product, of which at least one 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 undergoes no other operation conditioning such as grinding before being consolidated by direct precompaction and / or compacting, this operation may be such as to alter the mechanical characteristics of the consolidated alloy obtained.
• 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 processes are described in detail in application EP 89-903 172.
• 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 products which solidify rapidly, in particular directly on the scales or plates.
• Consolidation is important to avoid long exposures to high temperatures. We therefore chose to operate a warm spinning which minimizes the time spent 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 (for example 5 mm / sec).
• the solid product before consolidation can be: either introduced directly into the container of a press and then spun, either cold or warm pre-compacted (temperature below 350 ° C.
• a press for example in the form of a billet whose density is close to 99% of the theoretical density of the alloy, this billet being subsequently spun, either introduced by cold pre-compacting them up to 70% of the theoretical density in a sheath made of magnesium or magnesium alloy or aluminum or aluminum alloy, itself introduced into the container of the spinning press; we can then, after spinning, remove the sheath by machining.
• the sheath can be thin-walled (less than 1 mm) or thick (up to 4 mm). In all cases, it is preferable that the alloy constituting the sheath has a flow limit not exceeding the order of magnitude of that of the product to be spun, at the spinning temperature.
• the process according to the invention makes it possible to unexpectedly obtain a consolidated magnesium alloy which has, as already described, a structure of fine grains (less than 3 ⁇ m) stabilized by intermetallic compounds, and / or by metastable dispersoids and high mechanical characteristics.
• the structure and mechanical properties of said alloy remain unchanged after prolonged maintenance of 24 h and more at a temperature reaching 250 ° C., or even 300 ° C. in certain cases, for example when the alloy contains calcium.
• the matrix consists essentially of magnesium containing approximately 1% (atomic) of Al in solid solution; the grain size is very fine, and usually between 0.3 and 1 ⁇ m; it depends on the consolidation conditions.
• the intermetallic phases observed depend on the composition of the alloy and can be Mg17Al12 optionally containing Sr and / or Zn, Mg32 (Al, Zn) 49, Mg17Sr2, Mg2Sr, Al4Sr, and when the alloy contains Ca Al2Ca. Rapid cooling allows the formation of metastable phases.
• the breaking loads obtained with the alloys according to the invention are high; they generally exceed 400 MPa and are at least of the same level as those obtained for example with the alloys described in the aforementioned applications; moreover, there is an improvement in ductility and hardness.
• strontium makes it possible to significantly improve the breaking strength, sometimes at the expense of ductility.
• the corrosion resistance is also very good, because, in addition to a low weight loss in a saline aqueous medium, there is the absence of pitting; the alloys according to the invention retain a very shiny appearance; only a few shallow localized corrosions are observed, having the appearance of antlers.

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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)
• Powder Metallurgy (AREA)
• Forging (AREA)
• Extrusion Of Metal (AREA)

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• 1990
  • 1990-06-01 FR FR9007299A patent/FR2662707B1/fr not_active Expired - Lifetime
• 1991
  • 1991-05-23 US US07/704,620 patent/US5147603A/en not_active Expired - Fee Related
  • 1991-05-29 JP JP3126062A patent/JPH04231435A/ja active Pending
  • 1991-05-30 EP EP91420177A patent/EP0465376B1/de not_active Expired - Lifetime
  • 1991-05-30 DE DE69104784T patent/DE69104784T2/de not_active Expired - Fee Related
  • 1991-05-31 CA CA002043723A patent/CA2043723A1/fr not_active Abandoned

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