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 a high strength, thermally resistant, tough, ductile cast aluminum alloys containing Zr and/or Hf and their use in the fabrication of work pieces or parts thereof.
• the known high strength and tough cast Al alloy Al Si 7 Mg 0.3 T6 reaches its performance limits under these operational conditions. Because of its Cu content the known cylinder head alloy GK-Al Si 7 Mg 0.3 Cu 0.5 T6 is brittle and susceptible to notch effects. Also of disadvantage is that during tests such cylinder head alloys have proven to be susceptible to fissuring in the combustion chamber plate (inter cylinder spacing, valve seat, valve channels, glow plug bores) and in the water channels. In addition such Cu containing cast Al alloys form corrosion slurries as a result of their reaction with the cooling fluid used in the cylinder head.
• the objective of the invention is to create a high strength, thermally resistant and at the same time tough cast Al alloy which at temperatures equal to or above 150° C. retains its strength values, and which features a lower thermal expansion through a reduction of phase formation and thus enhanced thermo-mechanical stability at temperatures up to 240° C.
• Ti titanium
• a grain refining is done with titanium (Ti) which forms Al 3 Ti-nuclei within the melt. Since as a consequence of the higher thermal loads the cast structure of today's alloys for work pieces, in particular in cylinder heads, is susceptible to creeping, the grain boundaries of the structure need to be stabilized with high temperature resistant precipitations.
• intermetallic high temperature phases need to be identified which particularly during casting do not form an acicular structure which embrittles the material.
• this alloy is, according to the invention, modified through the elements Zr and/or Hf.
• Zr and/or Hf fulfill the above mentioned requirements respectively, resulting in connection with Al in temperature stable intermetallic Al 3 Zr and Al 3 Hf as well as in Zr and Hf containing aluminum silicides like Al x Zr y Si z , Al x Hf y Si z respectively in Alx (Zr, Hf) y Si z high temperature phases with a melting point of 1582° C. (for Al 3 Zr) and 1590° C. (for Al 3 Hf).
• Zr and/or Hf in form of Al 3 Zr or, as the case may be, Al 3 Hf containing Al pre-alloys, are highly efficient as a grain refining additive and critically determine the thermo-mechanical strength of the cast Al alloy according to the invention.
• additional high temperature resistant Zr and/or Hf containing aluminum suicides are formed which thermally stabilize the structure or, as the case may be, result in a lower irreversible thermal expansion at 240° C.
• the Zr and/or Hf grain refining according to the invention are preferred since the Al 3 Zr and/or Al 3 Hf phases are more temperature stable than Al 3 Ti, and in addition Zr or Hf feature a significantly lower solubility in Al.
• Hf is preferred compared to Zr.
• operation temperatures between 150° C. and 250° C. the solid solution hardening remains mostly preserved.
• the precipitation hardening decreases through Al 3 Zr and/or Al 3 Hf.
• Al 3 Zr/Al 3 Hf dispersoids Al 3 (Zr, Ti) or Al 3 (Hf, Ti), mixed dispersoids or, in reaction with the silicon, Zr, Hf or Ti containing aluminum silicides like Al x Zr y Si z , Al x Hf y Si z or, as the case may be, Alx (Zr, Hf) y Si z are formed.
• These precipitations are very temperature stable so that according to the invention they result in a lower irreversible thermal expansion in Zr respectively Hf containing Al Si 7 Mg T6. For instance after 100 h at 240° C.
• the irreversible thermal expansion of T7-heat treated cylinder heads made of Zr/Hf-free GK-Al Si 7 Mg is between 0.05 and 0.06%. Addition of only 0.10 wt % Zr reduces the irreversible thermal expansion to approximately 0.04% and with a Zr addition of 0.20 wt % even lower to about 0.025%. According to the invention the irreversible thermal expansion of T7-heat treated cylinder heads made from GK-Al Si 6 Mg 0.26 Zr/Hf could be reduced an additional 10% through a reduced Si content of 4.5 to 6.5 wt %, which is outside the range of Al Si 7 Mg (Al Si 7 Mg: 6.5 to 7.5 wt % Si).
• the ultimate strain of the cylinder head was improved about 1% in comparison to Al Si 7 Mg, so that overall a higher temperature cycling durability is achieved.
• the Si content is preferably in a range between 5.5 and 7.5 wt %, particularly preferred between 6.5 and 7.5 wt %.
• the content of Fe and Mg in the Al Si 7 Mg alloy needs to be restricted according to the invention. According to the invention the following chemical composition is proposed.
• Ti and Hf may also exist as a mixture (e.g. Zr “contaminated” with Hf) in the mentioned areas.
• the high strength values according to the objective, concurrent with high toughness, are furthermore achievable via a fine cast structure.
• high setting rates are desirable.
• the structure in gravity die casting and pressure die casting is finer compared to sand casting.
• the invention also relates to the use of the above mentioned cast Al alloy for the fabrication of a work piece or a part thereof.
• part thereof means an inherent part of the work piece, such as a constituent, a casing, a coating or such.
• Work pieces are particularly but not exclusively pieces such as pistons for internal combustion engines, cylinder heads, crank cases, or engine blocks.

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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)

Applications Claiming Priority (3)

Publications (1)

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• 2003
  • 2003-05-24 DE DE10323741A patent/DE10323741B3/de not_active Expired - Lifetime
• 2004
  • 2004-05-03 US US10/559,163 patent/US20060115375A1/en not_active Abandoned
  • 2004-05-03 WO PCT/EP2004/004654 patent/WO2004104240A2/de active Application Filing
  • 2004-05-03 JP JP2006529730A patent/JP2007500793A/ja not_active Withdrawn

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