JP2007500793A - High strength heat resistant tough aluminum alloy castings - Google Patents

Abstract

The present invention is an aluminum alloy casting (Al Si 7 Mg 0.25 Zr wa or Al Si 7 Mg 0.25 Hf wa) and (Al Si 6 Mg 0.25 Zr wa) having high strength, heat resistance and high ductility. Or Al Si 6 Mg 0.25 Hf wa). This alloy contains Si: 6.5 to 7.5 wt% and 5.5 to 6.5 wt%, Mg: 0.20 to 0.32 wt%, Zr: 0.03 to 0.50 wt%, and / Or Hf: 0.03 to 1.50 wt%, Ti: 0 to 0.20 wt%, Fe: <0.20 wt%, Mn: <0.50 wt%, Cu: <0.05 wt% Zn: <0.07% by weight, and in each case, Al is added to make it 100% by weight. The present invention also relates to a method of using the Al alloy casting with a high heat load for a workpiece or part made of the Al alloy casting such as a cylinder head.

Description

  The present invention relates to a high-strength, heat-resistant, tough, ductile aluminum alloy casting containing Zr and / or Hf, and the use of this alloy casting in the manufacture of workpieces or parts made from this alloy casting. About.

  In order to reduce engine emissions and fuel consumption and increase its output, the combustion pressure and temperature of internal combustion engines, particularly diesel engines, have increased over the past few years. As a result of this increase, the requirements required for the thermomechanical load on the workpiece are further increasing.

  According to the current technology, aluminum (Al) alloy castings, particularly for the production of internal combustion engines, are known. Cast Al parts made of Al alloy castings are widely used in terms of low specific gravity, simple molding, and easy production. In addition, various casting methods can produce complex workpieces or parts made of Al alloy castings such as pistons, cylinder heads, crankcases, or engine blocks for internal combustion engines. Such workpieces and in particular a range of these workpieces are exposed to high thermomechanical loads during operating conditions.

Known high strength tough Al alloy castings, such as Al Si 7 Mg 0.3 wa (Note: wa is an abbreviation for German warmagehaertet, meaning “heat-treat” such as T6, T7). Its performance limit is reached under conditions. The well-known cylinder head alloy GK-Al Si 7 Mg 0.3 Cu 0.5 wa is brittle and sensitive to the notch effect because it contains Cu. This type of cylinder head alloy also has the disadvantage that it was found to be sensitive to cracks in the combustion chamber plate (inter-cylinder space member, valve seat, valve port, glow plug perforation) and water channel during testing. ing. Further, such a Cu-containing Al alloy casting reacts with a cooling fluid used in the cylinder head to form a corrosive slurry. In each of the Al alloy castings described above, precipitates of Mg ₂ Si and Al ₂ Cu that enhance the strength are formed by heat treatment, but these are not stable at temperatures above 150 ° C., and are therefore thermal engines of modern engines. Not compatible with dynamic loads. Under a long-term heat load exceeding 150 ° C., a strength decrease of at least 30% occurs. Moreover, further precipitation of the Mg ₂ Si and Al ₂ Cu phases results in irreversible thermal expansion in the parts of the component that are subjected to high thermal loads, which reduces the durability of the operating alloy to thermal cycling.

  The object of the present invention is a high strength, heat resistant and tough Al alloy casting which retains its strength value at a temperature of 150 ° C. or higher, and further has a low thermal expansion due to a decrease in phase formation. The object is to produce Al alloy castings with the characteristics of enhanced thermomechanical stability at temperatures up to 0 ° C.

  This object is achieved by the characterizing part of claim 1. Furthermore, the drawbacks of the current technology can be overcome.

In the case of Al alloy castings, grain refinement is usually performed using titanium (Ti) that forms Al ₃ Ti nuclei in the melt. As a result of the high heat load, the cast structure of modern alloys for workpieces, especially those in cylinder heads, is susceptible to creep, so that the grain boundaries of the structure need to be stabilized with high temperature resistant precipitates.

  Besides Ti, on the one hand, chemical elements that promote the growth of fine grains, and on the other hand, thermally stabilize the microstructure to 250-300 ° C by high-temperature stable grain boundary precipitates and / or solid solution hardening. The chemical elements to be taken into consideration. It should be pointed out that the microstructure is stabilized by high temperature stable grain boundary precipitates and / or solid solution hardening at temperatures above 250 ° C. This improves resistance to creep and prevents grain boundary sliding and grain growth. In addition, the desired high temperature strength is achieved without solidifying the alloy by solid solution hardening and precipitate hardening. A high solid solution content is advantageous for high ultimate strain and heat resistance.

  In order to achieve the required requirements in accordance with the present invention, the presence of a high temperature phase of intermetallic compounds that does not form an acicular structure that embrittles the material, particularly during casting, must be confirmed.

First, taking the high strength and tough Al alloy casting AlSi7Mgwa, this alloy is modified according to the invention by the elements Zr and / or Hf. Surprisingly, Zr and / or Hf achieve the above requirements. That is, the high-temperature phase of the intermetallic compounds Al ₃ Zr and Al ₃ Hf which are bonded to Al and stable at high temperature, and Al _x Zr _y Si _z , Al _x Hf _y Si _z , or Al _x (Zr, Hf) _y Si _The result is a high temperature phase of aluminum silicide containing Zr and Hf, such as _z . These high-temperature phases have melting points of 1582 ° C. (for Al ₃ Zr) and 1590 ° C. (for Al ₃ Hf). Zr and / or Hf in the form of Al prealloys containing Al ₃ Zr or Al ₃ Hf are very effective as grain refinement additives due to their high temperature stability and very low solubility in Al. The thermomechanical strength of the Al alloy casting according to the present invention is determined deterministically. In the subsequent heat treatment, high temperature resistant Zr and / or Hf-containing aluminum silicide is additionally formed, the structure is thermally stabilized, and in some cases, irreversible thermal expansion at 240 ° C. can be kept low. . In order to avoid acicular precipitates or precipitates that lead to embrittlement, fine Al ₃ Zr or Zr or Hf in the form of Al ₃ Hf phase is an Al prealloy containing up to 10% by weight of Zr and / or Hf. Therefore, it is necessary to put into the molten Al in the form of powder or wire. Only a very small amount of Zr and / or Hf content of only 0.03% by weight is required for grain refinement.

Compared to the well-known Ti grain refinement, in particular the Zr and / or Hf grain refinement according to the present invention is such that the Al ₃ Zr and / or Al ₃ Hf phase is more stable in temperature than Al ₃ Ti, and moreover Zr or Hf is preferable in that it has a feature that its solubility in Al is much smaller.

The effect of crystal grain refinement was demonstrated by the cylinder head of GK-Al Si 7 Mg wa. Using a conventional Ti-containing grain refiner additive such as AlTi10, AlTi5, or AlTi3B1, a texture having 20-70 μm arm spacing of Al dendrite in the combustion chamber plate. It was realized. Zr or Hf in the form of Al ₃ Zr or Al ₃ Hf-containing Al prealloys such as Al Zr 5, Al Zr 10, Al Hf 5, or Al Hf 10 and 0.10 to 0 in GK-Al Si 7 Mg When 20 wt% was added, the arm spacing of the Al dendrite could be economically reduced to 10 to 50 μm. Similarly, fine dendrite arm spacing can be obtained by further refinement of Ti crystal grains. During alloying with Zr or Hf according to the invention at temperatures above 690 ° C., only a small part of the Al ₃ Zr or Al ₃ Hf phase dissolves from the Zr or Hf-containing Al prealloy, Therefore, sufficient Al ₃ Zr or Al ₃ Hf nuclei are left for Al grain refinement. On the other hand, already dissolved Zr and Hf remain dissolved in the aluminum depending on the solidification rate in the pressure or gravity die casting method. In addition to the composition of the alloy, solid solution hardening during the subsequent heat treatment period consisting of solution heat treatment between 470 ° C. and 560 ° C., quenching with water, and age hardening at a temperature exceeding 160 ° C. The ratio of to precipitation hardening is also determined. Heat treatment prolonged solution at high temperatures, followed when water cooling, the higher the content of the solid solution hardening and heat treatment prolonged solution at a temperature of _{200 ℃ ~250 ℃, Al x Zr} y Si z, Al x Hf y Si _As a result, Zr or Hf-containing aluminum silicide, such as _z or Al _x (Zr, Hf) _y Si _z , is formed, resulting in a higher rate of precipitate hardening and lower solid solution hardening. During solution heat treatment between 470 ° C. and 560 ° C., 0.15 wt% or less of Zr or 1.00 wt% or less of Hf can be dissolved. Therefore, Hf is more advantageous than Zr for increasing the strength without embrittlement of the alloy. At engine temperatures (operating temperatures) between 150 ° C. and 250 ° C., solid solution curing remains largely preserved. On the other hand, under heat load, precipitation hardening by Al ₃ Zr and / or Al ₃ Hf is reduced. However, the decrease in material strength is negligible or less than with Mg ₂ Si precipitate hardening. This is because the Al grain refinement additives undissolved later formed the _{Al x Zr y Si z, Al} x Hf y Si z or _{Al x (Zr, Hf) y} Si Zr and Hf, such as _z, This is because Al ₃ Zr and / or Al ₃ Hf derived from the contained aluminum silicide has high temperature stability. When Ti grain refinement is additionally performed, a mixed dispersoid of Al ₃ (Zr, Ti) or Al ₃ (Hf, Ti) is formed in addition to the Al ₃ Zr / Al ₃ Hf dispersoid, or Reaction with silicon forms Zr, Hf, or Ti-containing aluminum silicides such as Al _x Zr _y Si _z , Al _x Hf _y Si _z , or Al _x (Zr, Hf, Ti) _y Si _z. . Since these precipitates are very temperature stable, the present invention results in reduced irreversible thermal expansion in Al Si 7 Mg wa containing Zr or Hf. For example, the irreversible thermal expansion of a GK-Al Si 7 Mg cylinder head not containing Zr / Hf subjected to T7 heat treatment is 0.05 to 0.06% after exposure to 240 ° C. for 100 h. The addition of only 0.10% by weight of Zr reduces this irreversible thermal expansion to about 0.04%, and the addition of 0.20% by weight of Zr further reduces to about 0.025%. According to the present invention, the irreversible thermal expansion of the T7 heat treated cylinder head made of GK-Al Si 6 Mg 0.26 Zr / Hf is achieved by reducing the Si content to 4.5-6.5 wt%. Further, it could be reduced by 10%. This Si content is outside the range of Al Si 7 Mg (Al Si 7 Mg: 6.5-7.5 wt% Si). Furthermore, since the ultimate strain of the cylinder head is improved by about 1% as compared with Al 2 Si 7 Mg, high durability against the temperature cycle as a whole is realized. The Si content is preferably in the range of 5.5 to 7.5% by weight, particularly preferably in the range of 6.5 to 7.5% by weight.

  In order to ensure the required high toughness or resistance to the notch effect of the alloy according to the invention, the Fe and Mg content in the Al Si 7 Mg alloy must be limited according to the invention. According to the present invention, the following chemical composition is proposed.

The chemical composition of the Al alloy castings according to the present invention is as follows (abbreviated notation: Al Si 7 Mg 0.25 Zr wa or Al Si 7 Mg 0.25 Hf wa or Al Si 6 Mg 0.25 Zr wa or Al Si 6 Mg 0.25 Hf wa). That is,
Si: 4.5 to 7.5% by weight, in particular 6.5 to 7.5% by weight,
Mg: 0.20 to 0.32% by weight,
Zr: 0.03-0.50% by weight and / or Hf: 0.03-1.50% by weight,
Ti: 0 to 0.20% by weight,
Fe: <0.20% by weight,
Mn: <0.50% by weight,
Cu: <0.05% by weight,
Zn: <0.07% by weight,
In each case, Al is added to make 100% by weight.

  In some cases, residual impurities (Nb, V, B, Ni, Co) from the manufacturing process may be included, as is well known to those skilled in the art.

  Further, Zr, Ti and Hf may exist as a mixture within the above range (eg, “contains” Zr of Hf).

  With a cylinder head of GK-Al Si 7 Mg 0.25 Zr wa, by adding 0.10 to 0.20 wt% of Zr, the tensile strength and yield point can be improved by at least 10% without embrittlement of the alloy Became clear. Further, since there is an effect of refining Zr crystal grains, the ultimate strain remains unchanged. The irreversible thermal expansion at 240 ° C. could be reduced by about 50%.

  The targeted high strength value can be realized by a fine cast structure together with high toughness. For this reason, a high solidification rate during casting is desirable. In the case of equivalent casting thickness, the structure of the gravity die casting method and the pressure die casting method is finer than that of sand casting.

  The present invention also relates to a method of using the Al alloy casting described above for the production of a workpiece or part made of this alloy casting. Here, the expression “parts made of this alloy casting” means specific parts of the workpiece, such as components, casings, coatings, etc.

  The workpiece is in particular an item such as, but not limited to, an internal combustion engine piston, cylinder head, crankcase, or engine block.

  For the production of Al alloy castings and processed products according to the present invention, ordinary methods well known to those skilled in the art can be used unless otherwise specified.

Claims (5)

The following chemical composition:
Si: 4.5 to 7.5% by weight,
Mg: 0.20 to 0.32% by weight,
Zr: 0.03-0.50% by weight and / or Hf: 0.03-1.50% by weight,
Ti: 0 to 0.20% by weight,
Fe: <0.20% by weight,
Mn: <0.50% by weight,
Cu: <0.05% by weight,
Zn: <0.07% by weight,
And Al alloy casting containing Al added to make it 100 weight% in total.   The Al alloy casting according to claim 1, wherein Zr and Hf are present as a mixture in the above range. The Al alloy casting according to claim 1, wherein the alloy includes a high-temperature phase of Al ₃ Zr and / or Al ₃ Hf which are intermetallic compounds. Said alloy, _Al 3 is an intermetallic compound (Zr, Ti) and / or _Al 3 (Hf, Ti) phase, characterized in that it comprises a particular mixing dispersoid, one of claims 1 to 3 1 The Al alloy casting described in the item.   A method of using the Al alloy casting according to any one of claims 1 to 4 for a piston, a cylinder head, a crankcase, or an engine block of an internal combustion engine.