Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/02—Alloys based on aluminium with silicon as the next major constituent
  • C22C21/04—Modified aluminium-silicon alloys

Definitions

• the invention relates to the field of intended for the manufacture of aluminum-silicon alloy parts molded by die-casting, of relatively thin thickness, and in particular structural or safety parts for the automobile.
• the high copper content if it has a favorable influence on the mechanical strength, makes the alloy susceptible to corrosion.
• good resistance to corrosion in particular to stress corrosion, is necessary to avoid deterioration of the part in a corrosive environment such as snow-removing salt.
• Various alloy formulations have been proposed to meet these requirements. For example, US Pat. No.
• Patent EP 0687742 filed in 1994 by Aluminum Rheinfelden describes an alloy for die casting intended for safety molded parts, of composition
• EP 0992601 and EP 0997550 filed in 1998 by Alusuisse, describe the manufacture by pressure casting of alloy parts of composition: Si: 9.5 - 11.5 Mg: 0.1 - 0.4 Mn: 0, 3 - 0.6 Fe: 0.15 - 0.35 Ti ⁇ 0, l Sr: 90 - 180 ppm possibly Cr: 0, 1 - 0.3 Ni: 0, 1 - 0.3 Co: 0, 1 - 0.3
• the parts are subjected to a partial dissolution between 400 and 490 ° C.
• These different alloys require, to reach the required mechanical resistance, a heat treatment with dissolution and quenching, which leads to significant deformations parts which must undergo straightening, leading to a significant increase in the cost price.
• US patent 6132531 filed in 1997 by Alcoa, relates to an alloy for die casting, intended in particular for structure nodes of automobile bodywork of the “space-frame” type, of composition: Si ⁇ 0.20 Fe ⁇ 0.20 Mg : 2.80 - 3.60 Mn: 1.10 - 1.40 Ti ⁇ 0.15 Be: 0.0005 - 0.0015. Good mechanical properties are obtained without heat treatment of the cast parts. The absence of silicon affects the flowability of the alloy. Purpose of the invention
• the object of the invention is to provide aluminum alloys for the pressure casting of structural and safety parts for the automobile having both sufficient mechanical strength without necessarily requiring a complete heat treatment of the T6 or T7 type, high ductility, good corrosion resistance, good moldability and allowing the production of parts in large series under acceptable economic conditions.
• the subject of the invention is safety or structural parts die-cast in a ductile aluminum alloy of composition (% by weight):
• FIGS. 1a, 1b and 1c represent the respective variation of the breaking strength, the elastic limit and the elongation as a function of the silicon content, for different magnesium contents, on thick sample plates 2.5 mm pressure casting with vacuum assistance and not heat treated (state F).
• Figure 2 shows the mechanical characteristics of die cast parts
• the invention is based in particular on the observation that by lowering the silicon content compared to the alloys of the prior art intended for the same applications, it is possible to obtain for the die-cast parts an interesting compromise between the mechanical strength, in particular at the simply returned state (T5) and ductility, while keeping an acceptable flowability, and an absence of cracks and shrinkage.
• the silicon content is at least 2% to maintain good flowability, and at most 6% to obtain high ductility in the T5 state. It is preferably between 3.5 and 5%.
• the influence of the silicon content on the elastic limit and the elongation is illustrated by Figures la and lb in the F state (untreated) and Figure 2 in the T5 state, which show in particular the rapid decrease in elongation as the silicon content increases.
• Magnesium has the same effects as silicon by forming with it particles of Mg 2 Si which have a hardening effect on heat treatment.
• this hardening effect partially subsists in the absence of dissolution and quenching, probably by an effect of supersaturation of the solid aluminum solution. It is thus possible to limit the magnesium content to 0.4, or even 0.3 or 0.25%, which improves the elongation, while keeping a good elastic limit.
• Iron, manganese, chromium, cobalt, vanadium, molybdenum and nickel form individually or in combination with aluminum weakening intermetallic compounds, and their content must be limited. However, when the rate of cooling on demolding is high, embrittlement is less, since these components have a reduced size and a more favorable morphology. Conversely, these same elements contribute to reducing the “sticking” in the mold, of casting, by reducing the chemical potential of the alloy compared to steel. As iron has an unfavorable influence on the elongation and must be limited to 0.5%, and preferably 0.2%, it is essential that in addition to the iron at least one of the other elements is present.
• this element is manganese
• its content must be between 0.3 and 2%, and preferably between 0.7 and 1.5%.
• Titanium, combined with boron, is a refiner of the solid aluminum solution by reducing the grain size of the primary particles. In addition, it increases the supply capacity of the volumetric contraction during solidification, which contributes to improving the compactness of the parts.
• Copper should be kept below 0.3%, and preferably 0.1% to avoid sensitivity to corrosion, and because it reduces elongation.
• Lead, tin and antimony inhibit the action of the modifying elements.
• the modifying or refining elements of eutectics such as strontium, sodium and calcium, modify the size and morphology of the silicon wafers by giving them a fiber structure. They can also act as refiners of certain intermetallic compounds.
• the die-cast parts, with or without vacuum assistance, from the alloys according to the invention, can be used without heat treatment (state F), or on the contrary be subjected to a complete heat treatment T6 or T7 comprising a setting solution, quenching and tempering, or T3 treatment with natural aging after quenching.
• the alloys according to the invention make it possible to produce parts having both good mechanical strength and high elongation, leading to good impact resistance and making possible assemblies requiring high ductility, for example crimping. They also have good suitability for TIG, MIG or laser welding, and good compatibility with the 6000 aluminum alloys used for bodywork.
• the alloys have a low oxidizability in the liquid state, a good ease of recycling and a low loss on ignition at the remelting of waste. Examples
• Sample plates in 9 different alloys A to I were produced by pressure casting, with vacuum assistance (residual pressure in the mold of 80 hPa), the composition of which is given in Table 1.
• the plates were 120 ⁇ 220 mm and 2.5 mm thick.
• the casting was done on a 3200 kN press with a closing force, with a piston injection speed of 0.7 m / s.
• the metal temperature in the oven was 780 ° C.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Body Structure For Vehicles (AREA)
• Heat Treatment Of Steel (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Molds, Cores, And Manufacturing Methods Thereof (AREA)

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• 2001
  • 2001-12-05 FR FR0115700A patent/FR2827306B1/fr not_active Expired - Fee Related
• 2002
  • 2002-07-09 WO PCT/FR2002/002394 patent/WO2003006698A1/fr active Application Filing
  • 2002-07-09 JP JP2003512455A patent/JP2004536223A/ja active Pending
  • 2002-07-09 EP EP02767556A patent/EP1404885A1/de not_active Withdrawn
  • 2002-07-09 US US10/480,795 patent/US20050155676A1/en not_active Abandoned
  • 2002-07-09 CA CA002452479A patent/CA2452479A1/fr not_active Abandoned
  • 2002-07-09 DE DE02767556T patent/DE02767556T1/de active Pending

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