DE102014208325B4 - Wear-resistant alloys with complex microstructure - Google Patents

Abstract

Wear-resistant alloy having a complex microstructure, comprising:a range of 28 to 38 wt% zinc (Zn);a range of 1 to 3 wt% tin (Sn);a range of 6.2 to 9.4 wt .-% silicon (Si); optionally a range of 0.3 to 0.8 wt% magnesium (Mg); anda remainder of aluminum (Al).

Description

TECHNICAL FIELD

The present invention relates to an aluminum alloy used for vehicle parts that may require wear resistance and self-lubricating ability, and a method for preparing the same. In particular, the present invention provides an aluminum alloy with a complex microstructure containing wear-resistant particles and self-lubricating soft particles.

BACKGROUND

An aluminum alloy is generally a hypereutectic aluminum-silicon alloy (Al-Si alloy) with approximately 13.5 to approximately 18% by weight or 12% by weight of silicon (Si) and approximately 2 to approximately 4% by weight of copper (Cu) used in a vehicle industry. Since such a conventional Al-Si hypereutectic alloy has a microstructure with primary silicon (Si) particles having a size of about 30 to about 50 µm, it can have improved wearability compared to Al-Fe alloys alone hence, it is generally used for vehicle parts that may require wearability, such as a shift fork, rear cowl, swashplate and the like. An example of commercially available alloys may include: an R14 type alloy (manufactured by Ryobi Corporation, Japan), a K14 type alloy similar to the R14 alloy, an A390 type alloy used for a monoblock or an aluminum liner , and similar.

However, such hypereutectic alloys may have problems due to high silicon content, such as low castability, low impact strength, and the like. Additionally, tuning the size and distribution of silicon (Si) particles can be difficult, and hypereutectic alloys can be more costly to produce than other common aluminum alloys due to a specially designed process.

Meanwhile, Al-Sn alloy can be another example of self-lubricating aluminum alloy for vehicle parts. The Al-Sn alloy can contain about 8 to about 15% by weight of tin (Sn) and also a microstructure of self-lubricating soft tin particles (Sn particles) that can reduce friction. Therefore, such an Al-Sn alloy can be used as a base material of metal bearings used in joints with high frictional contact. However, this Al-Sn alloy may not be suitable for vehicle structural parts due to low strength, for example, about 150 MPa or less, although the strength may be enhanced by the silicon (Si) content.

From the DE 11 2011 101 836 T5 Incidentally, a metal alloy and in particular an aluminum alloy used for electrical, electronic and mechanical components and an aluminum alloy casting produced using the aluminum alloy are known. The aluminum alloy according to one embodiment comprises 4 to 13 wt% silicon (Si), 1 to 5 wt% copper (Cu), 26 wt% or more and less than 40 wt% zinc (Zn), and a residue consisting of aluminum (Al) and unavoidable impurities.

The description provided above as a related art of the present invention is merely to aid in understanding the background of the present invention and should not be construed as being included in the related art known to one of technical skill.

SUMMARY OF THE INVENTION

The present invention can provide a technical solution to the above-mentioned problems. Therefore, in one aspect, the present invention provides a novel high-strength and wear-resistant alloy having a microstructure that can be obtained from both hard particles and soft particles thereof. In particular, the novel alloy can have both the wear resistance of a hypereutectic Al-Si alloy and the self-lubricating ability of an Al-Sn alloy.

In an exemplary embodiment, the present invention provides a wear-resistant alloy with a complex microstructure that may contain: a range of 28 to 38 wt% zinc (Zn); a range of 1 to 3 wt% tin (Sn); a range of 6.2 to 9.4 wt% silicon (Si); optionally a range of 0.3 to 0.8% by weight of magnesium (Mg) and a balance or balance of aluminum (Al).

The wear-resistant alloy may contain a range of 0.3 to 0.8 wt% magnesium (Mg).

In another exemplary embodiment, the present invention provides a wear-resistant alloy with a complex microstructure containing: a range of 28 to 38 wt% zinc (Zn); a range of 1 to 3 wt% bismuth (Bi); a range of 6.2 to 9.4 wt% silicon (Si); and a remainder of aluminum (Al).

BRIEF DESCRIPTION OF THE DRAWING

• 1 ein beispielhafter Graph ist, der eine Korrelation zwischen einem Reibungskoeffizienten und einem Zinngehalt (Sn-Gehalt) in Gew.-% oder Zinkgehalt (Zn-Gehalt) in Gew.-% von verschleißfesten Legierungen mit einer komplexen Mikrostruktur nach einer beispielhaften Ausführungsform von Beispielen und Vergleichsbeispielen in Bezug auf weiche Partikel zeigt.

The above-mentioned and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

• 1 is an exemplary graph showing a correlation between a coefficient of friction and a tin content (Sn content) in wt.% or zinc content (Zn content) in wt.% of wear-resistant alloys with a complex microstructure according to an exemplary embodiment of examples and Comparative examples in relation to soft particles shows.

DETAILED DESCRIPTION

Various exemplary embodiments of the present invention will be described in detail below. The present invention relates to a novel alloy with a complex microstructure that can contain both hard particles and soft particles.

In certain examples of conventional aluminum alloys, alloying elements for forming self-lubricating particles may include tin (Sn), lead (Pb), bismuth (Bi), zinc (Zn), and the like. These alloying elements cannot be formed into intermetallic compounds because they cannot react with aluminum, and the phase thereof may be separated. Further, these alloying elements may have relatively low melting points and self-lubricating ability to form a lubricating film while partially melting under a strong friction condition.

Among the four alloying elements mentioned above, lead (Pb) may be the most suitable element for forming self-lubricating particles when both self-lubricating ability and cost are considered. However, lead is banned in vehicles as the same is classified as a harmful metal element.

In this regard, tin (Sn) may be the most widely used element instead of Pb, and occasionally bismuth (Bi) may be used instead of Sn. In contrast, zinc (Zn) may be disadvantageous due to a substantially high melting point compared to Sn and Bi and a substantially low self-lubricating ability. However, Zn can be added in a relatively significant amount due to low cost. Therefore, in terms of cost competitiveness, Zn can be used to form soft particles and partially replace the costly Sn or Bi.

In addition, Si or Fe may be an alloying element for forming hard particles. Si or Fe can cause eutectic reaction together with Al and form angular hard particles when added in a predetermined amount or more. In an example of aluminum alloys, Si can form hard particles and form primary silicon particles. Further, Si can provide wear resistance when added to an Al-Si binary alloy in an amount of about 12.6 wt% or more. However, when Si is added together with Zn, which is an element for forming soft particles, the Si content can be changed according to the Zn content for forming hard particles. For example, the Si content can be at least about 7% by weight to at most about 14% by weight when the Zn content is about 10% by weight. When the Si content is less than at least 7% by weight, hard particles cannot be formed; and, if the Si content is more than about 14% by weight at most, the size of the hard particles may increase significantly, thereby causing a negative effect on the mechanical properties and wear resistance.

Fe can be an impurity in Al-Fe alloys. However, when an Al-Fe binary alloy does not contain Si and Fe is added in an amount of about 0.5 wt% or less, wear-resistant Al-Fe particles of an intermetallic compound can be formed, the Al-Fe Alloy is thereby provided with wear resistance. On the contrary, when Fe is added in an amount of about 3% by weight or more, the particles of an intermetallic compound may be excessively formed, thereby lowering the mechanical properties and increasing the melting point. Further, alloying elements for enhancing the strength of an exemplary aluminum alloy may include Cu and Mg. Cu can be effective in forming intermetallic compounds and increasing strength through a chemical reaction of Cu with Al. The effect of Cu may vary depending on the Cu content, casting/cooling conditions or heat treatment conditions. Mg can be effective in forming intermetallic compounds and increasing strength through a chemical reaction of Mg with Si or Zn. The effect of Mg may also vary depending on the Mg content, casting/cooling conditions or heat treatment conditions.

Below, the present invention will be described in detailed exemplary embodiments.

In an embodiment not part of the invention, the aluminum alloy may contain aluminum (Al) as a major component and also a range of about 28 to about 38% by weight zinc (Zn); a range of about 1 to about 3 weight percent tin (Sn); a range of about 1 to about 3 weight percent copper (Cu); a range of about 0.3 to about 0.8 weight percent magnesium (Mg); and a range of about 6.2 to about 9.4 weight percent silicon (Si) to form hard particles. If zinc (Zn) is added in an amount less than about 28% by weight, a sufficient amount of soft Zn particles cannot be formed and hence it may be difficult to obtain sufficient self-lubricating ability. If zinc (Zn) is added in an amount of more than about 38% by weight, the solidus line of the aluminum alloy may become substantially low, thereby degrading casting conditions.

In addition, tin (Sn) can have a higher self-lubricating ability than zinc (Zn). If tin (Sn) is added in an amount of less than 1 wt%, a sufficient amount of soft Sn particles cannot be formed and hence it may be difficult to compensate for the insufficient self-lubricating ability of soft Zn particles. When tin (Sn) is added in an amount of more than 3 wt%, additional self-lubricating effects may not be sufficient compared to an increase in cost and hence the amount thereof is limited.

Silicon (Si) can form hard particles. When silicon (Si) is added in an amount of less than about 6.2 wt%, primary hard Si particles cannot be sufficiently formed, for example less than about 0.5 wt%, and thus it can be difficult to ensure wear resistance. If silicon (Si) is added in an amount of more than about 9.4% by weight, the primary hard Si particles may be excessively formed, for example more than about 5% by weight, and thus they may become hard Particles become coarser and thereby have a negative impact on wear resistance and mechanical properties.

Copper (Cu) can improve mechanical properties, and copper (Cu) can be added in an amount of about 1% by weight or more to ensure sufficient mechanical properties. However, when copper (Cu) is added in an amount of more than 3% by weight, other elements and intermetallic compounds may be formed to lower the mechanical properties of the aluminum alloy, and thus the amount of copper (Cu) may be limited. Alternatively, magnesium (Mg) can be added instead of copper (Cu) in an amount of about 0.3% by weight or more, and the mechanical properties of the aluminum alloy can be further improved. However, when magnesium (Mg) is added in an amount of about 0.8% by weight, compounds that lower the mechanical properties of the aluminum alloy may be formed, and thus the amount of magnesium (Mg) may be limited.

The low friction characteristics of the Al-Zn-Sn alloy according to a non-inventive embodiment of the present invention were evaluated with respect to soft particles. As in 1 As shown, exemplary alloys of Examples and Comparative Examples were prepared while changing the amounts of Zn and Sn, and then the changes in friction coefficients of the alloys were measured. Accordingly, under a condition of about 1 wt% Sn, exemplary 1Sn-28Zn alloys of the examples can achieve desirable low friction characteristics, for example, a coefficient of friction of about 0.150 or less, and exemplary 1Sn-26Zn alloys the comparative examples achieve undesirable results. Therefore, when Zn is added in an amount of about 28 wt% or more based on about 1 wt% or more of Sn, desirable low friction characteristics can be achieved. In addition, as the amount of Sn and Zn increases, satisfactory low friction characteristics can be obtained. The results of evaluating the wear resistance and mechanical properties of the exemplary Al-35Zn-1Sn-xSi alloys of the Examples and Comparative Examples are given in Table 1 below. Table 1 Class. Al Zn (wt.%) Sn (% by weight) Si (wt.%) Cu (wt.%) Mg (wt.%) Si particle content (%) Strength (MPa) Comparative example rest 35 1 6 2 0.5 0.2 - Examples rest 35 1 6.2 2 0.5 0.5 355 rest 35 1 6.4 2 0.5 1 - rest 35 1 9.2 2 0.5 4.8 350 rest 35 1 9.4 2 0.5 5 350 Comparative example rest 35 1 9.6 2 0.5 5.2 -

In the table, for exemplary Al-35Zn-1Sn-xSi alloys of the comparative examples, which can contain approximately 0.8% by weight of Si, Si particles in the form of hard particles in an amount of approximately 0.2% by weight .-% and consequently it may be difficult to obtain sufficient wear resistance. In contrast, when Si is contained in an amount of about 9.6 wt%, Si particles in the form of hard particles can be formed in excess amounts, for example, more than about 5 wt%, and thus can the Si particles are coarsened and segregated. Further, when the amount of Si is about 6.2 to about 9.4 wt%, hard Si particles can be formed in a maximum amount of about 5 wt%, thereby obtaining sufficient wear resistance .

In addition, the strengths of the exemplary Al-35Zn-1SnxSi alloys may range from about 350 to about 355 MPa according to the amount of Si, and thus such alloys can be used as structural materials for vehicle parts.

The aluminum alloy according to an exemplary embodiment of the present invention may contain: a range of about 28 to about 38 wt% zinc (Zn); a range of about 1 to about 3% by weight bismuth (Bi); a range of about 6.2 to about 9.4 weight percent silicon (Si); and a remainder of aluminum (A1). In particular, bismuth (Bi) can be used as a strong self-lubricating material instead of tin (Sn).

As described above, the wear-resistant alloy with a complex microstructure according to exemplary embodiments of the present invention can have both the wear resistance of a hypereutectic Al-Si alloy and the self-lubricating ability of an Al-Sn alloy, thereby having high strength and achieve improved wear resistance.

While the exemplary embodiments of the present invention have been disclosed for illustrative purposes, one skilled in the art will recognize that various modifications, additions and substitutions are possible without departing from the scope and spirit of the invention as disclosed in the appended claims.

Claims (3)

Wear-resistant alloy having a complex microstructure, comprising: a range of 28 to 38 wt% zinc (Zn); a range of 1 to 3 wt% tin (Sn); a range of 6.2 to 9.4 wt% silicon (Si); optionally a range of 0.3 to 0.8% by weight magnesium (Mg); and a remainder of aluminum (Al). Wear-resistant alloy Claim 1 , with a range of 0.3 to 0.8% by weight magnesium (Mg). Wear-resistant alloy with a complex microstructure, comprising: a range of 28 to 38 wt% zinc (Zn); a range of 1 to 3 wt% bismuth (Bi); a range of 6.2 to 9.4 wt% silicon (Si); and a remainder of aluminum (Al).

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