HIGH TEMPERATURE CAST ALUMINUM ALLOY FOR CYLINDER HEADS

Abstract

Aluminum alloys having improved high temperature mechanical properties are provided. An aluminum alloy suitable for sand casting, permanent mold casting, or semi-permanent mold casting includes about 3 to about 12 weight percent silicon; about 0.5 to about 2.0 weight percent copper; about 0.2 to about 0.6 weight percent magnesium; about 0 to about 0.5 weight percent chromium; about 0 to about 0.3 weight percent each of zirconium, vanadium, cobalt, and barium; about 0 to about 0.3 weight percent each of strontium, sodium, and titanium; about 0 to about 0.5 weight percent each of iron manganese, and zinc; and about 0.0.1 weight percent of other trace elements. Also disclosed is a semi permanent mold cast article, such as an engine cylinder head.

Claims

1. An aluminum alloy suitable for sand casting, permanent mold, or semi-permanent mold casting, the aluminum alloy comprising: about 3 to about 12 weight percent silicon; about 0.5 to about 2.0 weight percent copper; about 0.2 to about 0.6 weight percent magnesium; about 0.0 to about 0.5 weight percent chromium; about 0.0 to about 0.3 weight percent each of zirconium, vanadium, cobalt, and barium; about 0 to about 0.3 weight percent each of strontium, sodium, and titanium; about 0 to about 0.5 weight percent each of iron manganese, and zinc; and about 0.0.1 weight percent of other trace elements.

2. The aluminum alloy of claim 1, further comprising about 80 to about 91 weight percent aluminum.

3. The aluminum alloy of claim 2, further comprising as-cast particles essentially about 1.0 to about 100 m each of silicon and iron rich intermetallic particles.

4. The aluminum alloy of claim 2, further comprising solution treatment particles essentially about 100 nm to about 1 m particles including aluminum-chromium-silicon, aluminum-zirconium, aluminum-vanadium, and aluminum-titanium particles.

5. The aluminum alloy of claim 2, further comprising as-aged precipitates about 0.0 to about 100 nm each of Q-phase and S-phase.

6. An aluminum alloy suitable for sand casting, permanent mold, or semi-permanent mold casting, the aluminum alloy comprising: about 5 to about 9 weight percent silicon; about 0.6 to about 1.0 weight percent copper; about 0.4 to about 0.5 weight percent magnesium; about 0.25 to about 0.35 weight percent chromium; about 0.1 to about 0.2 weight percent each of zirconium, vanadium, and cobalt; about 0 to about 0.02 weight percent each of strontium and sodium; about 0 to about 0.2 weight percent titanium; about 0 to about 0.15 weight percent iron about 0 to about 0.15 weight percent manganese; about 0 to about 0.1 weight percent zinc; and about 0 to about 0.05 weight percent of other trace elements.

7. The aluminum alloy of claim 6, further comprising about 80 to about 91 weight percent aluminum.

8. The aluminum alloy of claim 7 further comprising as-cast particles essentially about 1.0 to about 100 m each of silicon and iron rich intermetallic particles.

9. The aluminum alloy of claim 8 further comprising solution treatment particles essentially about 100 nm to about 1 m particles including aluminum-chromium-silicon, aluminum-zirconium, aluminum-vanadium, aluminum-titanium-silicon, and aluminum-titanium particles.

10. The aluminum alloy of claim 9 further comprising as-aged precipitates about 0.0 to about 100 nm each of Q-phase and S-phase.

11. An aluminum alloy suitable for sand casting, permanent mold, or semi-permanent mold casting, the aluminum alloy comprising: about 6.5 to about 7.5 weight percent silicon; about 0.7 to about 0.8 weight percent copper; about 0.35 to about 0.45 weight percent magnesium; about 0.3 to about 0.35 weight percent chromium; about 0.1 to about 0.15 weight percent each of zirconium, vanadium, and cobalt; about 0.005 to about 0.02 weight percent strontium; about 0 to about 0.2 weight percent titanium; about 0 to about 0.05 weight percent each of barium, calcium, tin, nickel, and phosphorous; about 0 to about 0.15 weight percent iron; about 0 to about 0.10 weight percent manganese; about 0 to about 0.10 weight percent zinc; and about 0 to about 0.05 weight percent of other trace elements.

12. The aluminum alloy of claim 11 further comprising about 0 to about 1.4 sludge factor.

13. The aluminum alloy of claim 11 further comprising about 80 to about 91 weight percent aluminum.

14. The aluminum alloy of claim 13 further comprising as-cast particles essentially about 1.0 to about 100 m each of silicon and iron rich intermetallic particles.

15. The aluminum alloy of claim 14 further comprising solution treatment particles essentially about 100 nm to about 1 m particles including aluminum-chromium-silicon, aluminum-zirconium, aluminum-vanadium, aluminum-titanium-silicon, and aluminum-titanium particles.

16. The aluminum alloy of claim 15 further comprising as-aged precipitates about 0.0 to about 100 nm each of Q-phase and S-phase.

17. An aluminum alloy suitable for sand casting, permanent mold, or semi-permanent mold casting, the aluminum alloy consisting of: about 7.0 weight percent silicon; about 1.0 weight percent copper; about 0.4 weight percent magnesium; about 0.35 weight percent chromium; about 0.15 weight percent each of zirconium, vanadium, titanium, iron and cobalt; about 0.02 weight percent strontium; and remaining balance aluminum and copper.

18. The aluminum alloy according to claim 5 in the form of sand casting, permanent mold, or semi-permanent mold cast article.

19. The aluminum alloy according to claim 10 in the form of a sand casting, permanent mold, or semi-permanent mold cast article.

20. The aluminum alloy according to claim 16 in the form of a sand casting, permanent mold, or semi-permanent mold cast article.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings are provided for illustration purposes only and are not intended to limit this disclosure or the claims appended hereto.

[0018] FIG. 1 is a bottom view of a cylinder head casting in accordance with aspects of an exemplary embodiment;

[0019] FIG. 2 is a perspective view of a cylinder head casting in accordance with aspects of an exemplary embodiment;

[0020] FIG. 3 is a graph showing a calculated phase diagram of an aluminum alloy showing phase transformations as a function of copper (Cu) content as according to aspects of an exemplary embodiment; and

[0021] FIG. 4 is a graph showing a calculated phase diagram of an aluminum alloy showing phase transformations as a function of silicon (Si) content in accordance with aspects of an exemplary embodiment.

DETAILED DESCRIPTION

[0022] Cast aluminum alloys are provided having improved high temperature properties for cylinder heads. In FIGS. 1&2, an aluminum alloy cylinder head 10 produced using a semi-permanent mold casting method is illustrated in accordance with an exemplary embodiment and will now be described. In general, the cylinder head 10 includes features such as a head deck 12, combustion chambers 14, intake and exhaust ports 16, camshaft bearings 18, spark plug holes 20, water jacket openings 22, and oil passages 24, among other features. More particularly, the important features of the cylinder head 10 that are at least partially formed during the casting process include the head deck 12 and combustion chambers 14. Product specifications for the head deck 12 and combustion chambers 14 generally require higher yield and tensile strength than other areas of the cylinder head 10.

[0023] In comparison to other aluminum alloys, these alloys exhibit improved material strength and higher mechanical properties (see Table 1). These alloys may also exhibit improved castability and reduced porosity, as well as reduced hot cracking during tooling extraction. As a result, the scrap rate for aluminum casting and the manufacturing cost can be reduced. In some examples, alloy high temperature properties and engine performance can be improved. For example, the required inter-bore cooling can be reduced, eliminated, or avoided. Further, in some examples, the alloy density can be reduced. In some examples, the alloys may successfully undergo T6 or T7 treatments.

TABLE-US-00001 TABLE 1 Mechanical Properties of New Alloy Current Alloy New Alloy* UTS @RT (MPa) 313 323 YS @RT (MPa) 251 275 Elongation @RT (%) 6.2 2.3 UTS @300 C. (MPa) 41 56 YS @300 C. (MPa) 38 49 Fatigue Strength @10{circumflex over ()}7 cycles, 64 76 150 C. (MPa) Fatigue Strength @10{circumflex over ()}7 cycles, 49 53 200 C. (MPa) *Elevated temperature samples conditioned for 100 hours at temperature before testing. New alloy did not contain Cr or Co in first trial.

[0024] The alloy may contain at least one of the castability and strength enhancement elements such as silicon, copper, magnesium, manganese, iron, zinc, and nickel. The microstructure of the alloy contains one or more insoluble solidified and/or precipitated particles with at least one alloying element.

[0025] Two examples of composition ranges of the new alloy (called Version 1 and Version 2 in these examples) are listed in Table 2, compared with the other commercially available alloys for engine head castings.

TABLE-US-00002 TABLE 2 Chemical compositions of two versions of the new alloy and commercial alloys A356, AS7GU (A356 + 0.5% Cu), 354, 319, 363 alloys. Alloy Si Sr Ti B Mg Fe Mn Cu Zn Ca/P/Sn/Ni V/Zr/Co Cr other A356 6.5-7.5 <0.2 0.25-0.45 <0.2 <0.1 <0.2 <0.1 <0.05 <0.15 AS7GU 7.5-9.5 <0.2 0.25-0.45 <0.2 <0.1 0.5 <0.1 <0.05 <0.15 354 8.6-9.4 <0.2 0.4-0.6 <0.2 <0.1 1.6-2.0 <0.5 <0.1 <0.15 319 5.5-6.5 <0.25 <0.1 <1.0 <0.5 3.0-4.0 <1.0 <0.35 <0.5 363 4.5-6.0 <0.2 0.15-0.4 <1.1 <0.5 2.5-3.5 3-4.5 <0.25 <0.3 V1 5.0-9.0 0.02 Max 0.2 0.4-0.5 0.15 Max 0.15 Max 0.6-1.0 0.1 Max 0.1-0.2 0.25-0.35 0.05 Max (wt %) Max V2 6.5-7.5 .005-0.02 0.20 0.05 0.35-0.45 0.15 Max 0.10 Max 0.7-0.8 0.10 Max 0.05 Max 0.1-0.15 0.30-0.35 0.05 Max (wt %) Max Max

[0026] Tailored Cu content in the new aluminum alloys to form Q phase (AlSiMgCu) precipitates in comparison with traditional A356 & its variants.

[0027] Though copper is generally known to increase strength and hardness in aluminum alloys, on the downside, copper generally reduces the corrosion resistance of aluminum; and, in certain alloys and heat treatment conditions, copper increases stress corrosion susceptibility. Copper also increases the alloy freezing range and decreases feeding capability, leading to a high potential for shrinkage porosity. Furthermore, copper is expensive and heavy.

[0028] Artificial aging (T5) is used to produce precipitation hardening by heating the solution-treated and quenched castings to an intermediate temperature (e.g., 160-240 degrees C.), and then holding the castings for a period of time to achieve hardening or strengthening through precipitation. Considering that precipitation hardening is a kinetic process, the contents (supersaturation) of the retained solute elements in the as-quenched aluminum solid solution play an important role in the aging responses of the castings. Therefore, the availability and actual amount of hardening solutes in the aluminum soft matrix solution after casting and solution treatment has an effect on subsequent aging, which depends on the alloy composition, such as Cu and Mg content, and solution treatment temperature.

[0029] In AlSiMg based cast aluminum alloy, like A356 alloy, the strengthening precipitates are mainly Mg2Si, which are coarsened very rapidly when temperature is above 200 C. Adding Cu in the alloy in this application is to suppress the formation of Mg2Si precipitates and form heat-resistant Q phase (AlCuMgSi). As the Q-phase has a composition range, Cu varies from 9 to 10 in atom percent, Mg varies from 35 to 45 atom percent, Si varies from 38 to 36 atom percent, and balance of aluminum. To merely form the Q-phase in the alloy, the key strengthening element Cu content in the bulk material varies from 0.5 to 2 weight percent, Mg content varies from 0.2 to 0.6 weight percent, and Si is above 0.7 weight percent.

[0030] Excess Cu in the alloy however will form other low melting phases and thus reduce the formation of Q-phase. Typical sand cast aluminum alloys, such as 319, 354, or 363 contain 3-4% Cu in nominal composition and the Cu-containing phases consist of not only Q-phase but also -phase (Al2Cu), S-phase (AlSiMg), and AlMCu phases such as Al6CoCu3. Other Cu-containing low-melting phases can significantly affect alloy castability and increase porosity in the castings. One of the measures for castability of an alloy is freezing range between liquidus and solidus. The larger the freezing range, the higher the shrinkage porosity and lower castability. FIG. 3 illustrates a calculated phase diagram 50 of Al-7 wt % Si-0.4 wt % Mg based alloy with Cu content varying from 0 to 5 weight percent. The top line is called the liquidus boundary 52 and the bottom line is the solidus boundary 54. The temperature range between the liquidus boundary 52 and the solidus boundary 54 is the alloy freezing range 56. The freezing range 56 increases with Cu content in the alloy and reaches to a maximum value when Cu is about 3.5 weight percent. FIG. 1 also shows that no -phase (Al2Cu) will form if the Cu content in the bulk material is kept less than 1.0 weight percent.

[0031] To from Q-phase (AlCuMgSi), Mg is increased in the new aluminum alloys in comparison with traditional 319 & its variants.

[0032] To further improve the aging response of cast aluminum alloy, magnesium content in the new alloy should be kept no less than 0.2 wt %, and the preferred level is above 0.3 wt %. The maximum Mg content should be kept below 0.6 wt %, with a preferable level of 0.55 wt %, so that a majority of the Mg addition will stay in Al solid solution after solution treatment and form only Q-phase (AlCuMgSi) precipitates.

[0033] It was discovered that there was essentially no further improvement in strength when Mg was about 0.6 wt %.

[0034] Si is an important element for cast aluminum alloy. Si increases alloy castability by increasing fluidity and releasing high latent heat during solidification to reduce shrinkage and improve feeding. High Si content also reduces alloy freezing range. For example, referring to FIG. 4 which illustrates a calculated phase diagram 100 of Al-0.75% Cu-0.4 wt % Mg based alloy with Si content varying from 0 to 10 weight percent. As with FIG. 3, the top line is called liquidus boundary 105 and the bottom line is the solidus boundary 110. The temperature range between the liquidus 105 and solidus 110 boundary lines is the alloy freezing range 115. The freezing range 115 is almost kept constant when the Si content is between 5.0 and 9.0 weight percent.

[0035] The alloys described herein may be used to manufacture a sand or permanent mold or semi-permanent mold cast article, such as engine cylinder heads. Therefore, it is within the contemplation of the inventors herein that the disclosure extend to cast articles, including cylinder heads, containing the improved alloy (including examples, versions, and variations thereof).

[0036] Furthermore, while the above examples are described individually, it will be understood by one of skill in the art having the benefit of this disclosure that amounts of elements described herein may be mixed and matched from the various examples within the scope of the appended claims.

[0037] It is further understood that any of the above described concepts can be used alone or in combination with any or all of the other above described concepts. Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.