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

Definitions

• the invention relates to cast parts made of aluminium alloy subjected to high thermal and mechanical stresses, particularly cylinder heads and crankcases of internal combustion engines, and more particularly turbocharged diesel or gasoline engines. It also relates to parts other than automobile parts subjected to the same types of stress, for example in mechanics or in aeronautics.
• alloys containing 5 to 9% of silicon, 3 to 4% of copper and magnesium are usually secondary alloys, with iron contents of between 0.5 and 1%, and fairly high contents of impurities, particularly manganese, zinc, lead, tin or nickel. These alloys are generally non-heated alloys (temper F) or simply stabilised (temper T5). They are used particularly for manufacturing cylinder heads for gasoline engines with fairly low temperature stresses. For more highly stressed parts intended for diesel or turbo-diesel engines, primary alloys are used with an iron content of less than 0.3%, heat treated to temper T6 (tempered to the peak mechanical strength) or T7 (over-ageing).
• Al—Si5Cu3MgFe0.7 F high strength, low ductility
• the first and third alloy-temper combinations may be used for highly stressed cylinder heads.
• Patent FR 2690927 issued by the inventors and deposited in 1992 describes aluminium alloys resistant to creep containing 4 to 23% of silicon, at least one element among magnesium (0.1-1%), copper (0.3-4.5%) and nickel (0.2-3%), and 0.1 to 0.2% of titanium, 0.1 to 0.2% of zirconium and 0.2 to 0.4% of vanadium.
• An improved creep resistance is observed at 300° C. with no significant loss in the elongation measured at 250° C.
• Patent EP 1057900 (VAW Aluminium) deposited in 1999 is a development along the same direction and describes the addition of closely controlled quantities of iron (0.35-0.45%), manganese (0.25-0.30%), nickel (0.45-0.55%), zinc (0.10-0.15) and titanium (0.11-0.15%) to an Al—Si7Mg0.3Cu3.5 alloy.
• This alloy has good creep resistance, high thermal conductivity, satisfactorily ductility and good resistance to corrosion, in the T6 and T7 tempers.
• the purpose of this invention is to further improve the mechanical strength and creep resistance of cast parts made of AlSiCuMg type alloys within the temperature range 250-300° C., without degrading their ductility, and avoiding the increased use of alloying elements that can cause problems in recycling.
• the purpose of the invention is a cast part with high mechanical strength when hot and high creep resistance, made of an alloy with composition (% by weight): Si: 5-11 and preferably 6.5-7.5 Fe ⁇ 0.6 and preferably ⁇ 0.3 Mg: 0.15-0.6 ′′ 0.25-0.5 Cu: 0.3-1.5 ′′ 0.4-0.7 Ti: 0.05-0.25 ′′ 0.08-0.20 Zr: 0.05-0.25 ′′ 0.12-0.18 Mn ⁇ 0.4 ′′ 0.1-0.3 Zn ⁇ 0.3 ′′ ⁇ 0.1 Ni ⁇ 0.4 ′′ ⁇ 0.1
• the part is preferably solution heat treated, quenched and tempered to T6 or T7.
• the invention is based on the observation made by the inventors that if a small quantity of zirconium is added to a silicon alloy containing less than 1.5% of copper and less than 0.6% of magnesium, it is possible to obtain good mechanical strength and good creep resistance within the 250-300° C. range of cast parts tempered to T6 or T7 with no loss of ductility. This result is obtained without needing to use elements such as nickel or vanadium that cause problems in recycling. Furthermore, nickel has the disadvantage that it reduces the ductility of the part.
• the alloy contains 5 to 11% of silicon and preferably 6.5 to 7.5%. Iron is kept below 0.6% and preferably below 0.3%, which means that primary or secondary alloys can be used, preferably primary alloys when a high elongation at failure is required.
• Magnesium is a normal alloying element for alloys used in cylinder heads; if its content is equal to at least 0.15% and in combination with copper, it improves mechanical properties at 20 and 250° C. Beyond 0.6%, there is a risk of reducing the ductility at ambient temperature.
• manganese also has a positive effect on the mechanical strength at 250° C., but this effect reaches the maximum above a content of 0.4%.
• the titanium content is kept between 0.05 and 0.25%, which is fairly normal for this type of alloy.
• Titanium contributes to refining the primary grain during solidification, but in the case of alloys according to the invention, it works in liaison with zirconium and also contributes to the formation of very fine dispersoids ( ⁇ 1 ⁇ m) of AlSiZrTi in the in-body part of the ⁇ -Al solid solution during the solution heat treatment of the cast part, these dispersoids being stable above 300° C., unlike the Al 2 CuMg, AlCuMgSi, Mg 2 Si and Al 2 Cu phases that coalesce starting from 150° C.
• dispersoid phases do not cause embrittlement, unlike the large AlSiFe and AlSiMnFe iron phases (20 to 100 ⁇ m), and nickel phases that are formed during casting into interdendritic spaces.
• Parts are made by normal casting processes, particularly chill casting by gravity and low pressure casting for cylinder heads, but also sand casting, squeeze casting (particularly in the case of insertion of composites) and lost foam casting.
• Heat treatment comprises solution heat treatment typically for 3 to 10 h at a temperature of between 500 and 545° C., quenching preferably in cold water, waiting between quenching and annealing for 4 to 16 h and annealing from 4 to 10 h at a temperature between 150 and 240° C.
• the annealing temperature and duration are adjusted so as to obtain either annealing to the peak mechanical strength (T6) or over-ageing (T7).
• Parts according to the invention and particularly cylinder heads and crankcases of automobile or aircraft engines, have a high mechanical strength, good ductility, and higher mechanical strength when hot and creep resistance than parts according to prior art.
• compositions were measured by spark emission spectrometry, except for Cu and Zr that were measured by induced plasma emission spectrometry.
• Fifty AFNOR tensile chill test pieces were cast for each alloy. These test pieces were subjected to a heat treatment comprising solution heat treatment for 1 h at 540° C., preceded by a constant period of 4 h at 500° C. for the copper alloys B and C to prevent burning, quenching in cold water, natural ageing at ambient temperature for 24 h and annealing for 5 h at 200° C.
• alloy C with the added zirconium has a significantly better creep resistance, the deformation under constant load being reduced by 40 to 75% depending on the case.
• the increase of the magnesium content from 0.3 to 0.4% improves the creep resistance at 250° C., as can be seen from the results of the creep tests at a stress of 40 MPa after 100, 200 and 300 h for alloys G and H, as indicated in table 5: TABLE 5 Duration 100 h 200 h 300 h ⁇ (%) G 0.098 0.48 1.20 ⁇ (%) H 0.078 0.18 0.31
• Test pieces of 6 alloys I to N with the compositions indicated in table 6 were prepared in the same way as for alloy C in example 1: TABLE 6 Alloy Si Cu Mg Mn Zr Ti I 7 0.5 0.3 — 0.14 0.12 J 7 0.5 0.3 0.15 0.14 0.12 K 7 1 0.3 — 0.14 0.12 L 7 1 0.3 0.15 0.14 0.12 M 7 1 0.3 0.25 0.14 0.12 N 7 1 0.5 0.25 0.14 0.12

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Cylinder Crankcases Of Internal Combustion Engines (AREA)
• Manufacture Of Alloys Or Alloy Compounds (AREA)
• Cookers (AREA)
• Laminated Bodies (AREA)
• Molds, Cores, And Manufacturing Methods Thereof (AREA)

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• 2002
  • 2002-06-25 FR FR0207873A patent/FR2841164B1/fr not_active Expired - Lifetime
• 2003
  • 2003-06-23 EP EP03760770A patent/EP1516072B1/fr not_active Expired - Lifetime
  • 2003-06-23 JP JP2004514974A patent/JP2005530927A/ja active Pending
  • 2003-06-23 ES ES03760770T patent/ES2305507T3/es not_active Expired - Lifetime
  • 2003-06-23 US US10/518,597 patent/US20050224145A1/en not_active Abandoned
  • 2003-06-23 AT AT03760770T patent/ATE394513T1/de active
  • 2003-06-23 CA CA2489349A patent/CA2489349C/fr not_active Expired - Fee Related
  • 2003-06-23 WO PCT/FR2003/001916 patent/WO2004001079A2/fr not_active Ceased
  • 2003-06-23 AU AU2003255687A patent/AU2003255687B2/en not_active Ceased
  • 2003-06-23 DE DE60320790T patent/DE60320790D1/de not_active Expired - Lifetime
• 2005
  • 2005-01-24 NO NO20050362A patent/NO339371B1/no not_active IP Right Cessation

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