Patent Grant
10604828
This application claims the benefit under 35 USC § 119(a) of Korean Patent Application No. 10-2016-0071883 filed on Jun. 9, 2016 in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes.
The present invention relates to an Al—Zn alloy comprising precipitates with improved strength and elongation and a method of manufacturing the same. More particularly, the present invention relates to an Al—Zn alloy and a method of manufacturing the same, wherein the strength and the elongation of the Al—Zn alloy are both improved at the same time, including of discontinuous precipitates in a specific form.
An aluminum alloy is a lightweight alloy and is used as a structural material because of its excellent corrosion resistance and thermal conductivity. Since aluminum has a poor mechanical property, an aluminum alloy including one or more of metals such as zinc, copper, silicon, magnesium, nickel, cobalt, zirconium, cerium and the like has been widely used as a structural material such as an interior/exterior material of automobiles, ships, aircraft, etc. The Al—Zn alloy is an aluminum alloy used to improve the hardness of aluminum, usually including 10 to 14 wt % zinc based on the total weight of the alloy.
In order to be used as a structural material for ships, aircraft, etc., tensile strength, elongation, and shock absorption energy are considered to be important mechanical characteristics. Generally, it is difficult to improve both tensile strength and elongation at the same time because the tensile strength and the elongation are in a trade-off relationship in which one property is improved and the other property is attenuated.
In order to improve the tensile strength, studies on precipitation hardening, dispersion strengthening, work hardening, solid solution strengthening and grain refinement have been continued. Among them, the precipitation hardening is a phenomenon in which other phases in a matrix are precipitated during the heat treatment and precipitates act as obstacles to dislocation motion, such that an alloy becomes harder and stronger using particle strengthening.
In the precipitation hardening process of an Al—Zn alloy, continuous precipitates (CP) are precipitated from the supersaturated solid solution and distributed small and uniformly throughout the specimen, while discontinuous precipitates (DP) are produced since grain boundary diffusion and grain boundary migration cause irregular precipitation and thus composition and crystal orientation are changed discontinuously at the grain boundaries.
In general, since the tensile strength of discontinuous precipitates (DP) is lower than that of continuous precipitates (CP), studies that suppress discontinuous precipitates are predominantly underway.
Korean Patent No. 10-1274063 discloses a metal composite material having oriented precipitates in which Ni+Si, titanium or vanadium is added to a copper alloy to improve strength and electric conductivity, and a method for manufacturing the same.
As described above, there are problems in that increasing the tensile strength of the aluminum alloy reduces the elongation, and improving the elongation lowers the tensile strength.
An object of the present invention is to provide an Al—Zn alloy comprising oriented precipitates with improved tensile strength and elongation at the same time.
Another object of the present invention is to provide a method for efficiently producing an Al—Zn alloy comprising oriented precipitates with improved tensile strength and elongation.
Other objects and advantages of the present invention will become more apparent from the following detailed description, claims and drawings of the invention.
According to an aspect of the present invention, there is provided an Al—Zn alloy with improved strength and elongation, comprising more than 20 parts by weight of zinc relative to the total weight of the alloy and comprising 5% or more per unit area of discontinuous precipitates or lamellar precipitates forced to be formed.
According to another aspect of the present invention, there is provided an Al—Zn alloy with improved strength and elongation, comprising discontinuous precipitates or lamellar precipitates, wherein the discontinuous precipitates or the lamellar precipitates have an average aspect ratio of at least 20 and are oriented.
According to another aspect of the present invention, there is provided an Al—Zn alloy with improved strength and elongation, comprising discontinuous precipitates or lamellar precipitates, wherein an average length of the discontinuous precipitates or the lamellar precipitates is greater than or equal to 1.4 μm.
According to an embodiment of the present invention, an average spacing between the discontinuous precipitates or the lamellar precipitates may be 105 nm or less.
According to an embodiment of the present invention, an average thickness of the discontinuous precipitates or the lamellar precipitates may be 55 nm or less.
According to an embodiment of the present invention, the discontinuous precipitates or the lamellar precipitates may be oriented.
According to an embodiment of the present invention, the discontinuous precipitates or the lamellar precipitates may be formed by a heat treating treatment of the Al—Zn alloy to produce a solid solution and an aging treatment.
According to an embodiment of the present invention, the Al—Zn alloy may further include a precipitation accelerating metal.
The precipitation accelerating metal may be at least one selected from copper (Cu), titanium (Ti), silicon (Si), iron (Fe), manganese (Mn), magnesium (Mg), and chromium (Cr).
The precipitation accelerating metal may be copper (Cu), and the copper may be included in an amount of 0.05 to 5 parts by weight based on the total weight of the alloy.
According to an embodiment of the present invention, when the tensile strength of the Al—Zn alloy is 300 MPa to 400 MPa, the elongation may be 10% or more.
According to an embodiment of the present invention, when the tensile strength of the Al—Zn alloy is 400 MPa to 500 Mpa, the elongation may be 5% or more.
According to another aspect of the present invention, there is provided a method of manufacturing an Al—Zn alloy with simultaneously improved tensile strength and elongation, comprising: preparing an Al—Zn alloy comprising zinc in an amount of more than 20 parts by weight based on the total weight of the alloy; heat treating the Al—Zn alloy to form a solid solution; aging the Al—Zn alloy comprising the solid solution to force forming 5% or more of discontinuous precipitates or lamellar precipitates per unit area; and orienting to form oriented precipitates by calcining the Al—Zn alloy comprising the precipitates.
According to an embodiment of the present invention, the heat treating may be performed by heating at a temperature range of 350 to 450° C. for 30 minutes or more.
According to an embodiment of the present invention, the aging treatment may be performed in a temperature range of 120 to 200° C.
According to an embodiment of the present invention, the aging treatment may be performed for 5 minutes to 400 minutes.
According to an embodiment of the present invention, the preparing an Al—Zn alloy may comprise adding at least one precipitation accelerating metal chosen from copper (Cu), titanium (Ti), silicon (Si), iron (Fe), manganese (Mn), magnesium (Mg), and chromium (Cr) into the alloy.
According to an embodiment of the present invention, the precipitation accelerating metal may be copper, and the copper may be included in an amount of 0.05 to 5 parts by weight based on the total weight of the alloy.
According to an embodiment of the present invention, the orienting may be performed with a plastic working of 50% or more.
According to an embodiment of the present invention, the orienting may be performed in a liquid nitrogen atmosphere.
According to an embodiment of the present invention, tensile strength and elongation of the Al—Zn alloy may be improved at the same time by precipitates in an oriented specific form.
According to an embodiment of the present invention, tensile strength and elongation of the Al—Zn alloy may be improved at the same time by easily controlling an amount of precipitates oriented in the Al—Zn alloy manufacturing process.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
While the present disclosure has been described with reference to particular embodiments, it is to be appreciated that various changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the present disclosure, as defined by the appended claims and their equivalents. Throughout the description of the present disclosure, when describing a certain technology is determined to evade the point of the present disclosure, the pertinent detailed description will be omitted.
The terms used in the description are intended to describe certain embodiments only, and shall by no means restrict the present disclosure. Unless clearly used otherwise, expressions in the singular number include a plural meaning. In the present description, an expression such as “comprising” or “consisting of” is intended to designate a characteristic, a number, a step, an operation, an element, a part or combinations thereof, and shall not be construed to preclude any presence or possibility of one or more other characteristics, numbers, steps, operations, elements, parts or combinations thereof.
Hereinafter, an Al—Zn alloy and a method of manufacturing the same according to the present invention will be described in detail with reference to the accompanying drawings.
An Al—Zn alloy of the present invention is an Al—Zn alloy in which discontinuous precipitates that reduce the mechanical strength are forcibly formed inside the metal. The forcibly formed discontinuous precipitates may be artificially oriented to simultaneously enhance the strength and the elongation of the Al—Zn alloy.
In the present invention, discontinuous precipitates represent a comprehensive or equivalent meaning including lamellar precipitates (hereinafter referred to as lamellar precipitates) or cellular precipitates.
The Al—Zn alloy of the present invention comprises more than 20 parts by weight of zinc relative to the total weight of the alloy. When the content of zinc in the Al—Zn alloy is 20 parts by weight or less, discontinuous precipitates are hardly produced. The content of zinc in the Al—Zn alloy is preferably 30 parts by weight or more.
In addition, 5% or more per unit area of the discontinuous precipitates or the lamellar precipitates are included in the Al—Zn alloy. When the forcibly formed discontinuous precipitates or lamellar precipitates are less than 5% per unit area, it may be difficult to improve strength and elongation at the same time.
An Al—Zn alloy of the present invention includes discontinuous precipitates or lamellar precipitates, wherein the discontinuous precipitates or precipitates have an average aspect ratio of 20 or more. When the average aspect ratio of the discontinuous precipitates or the lamellar precipitates of the Al—Zn alloy is less than 20, it may be difficult to improve the tensile strength and the elongation of the Al—Zn alloy at the same time. The average aspect ratio may be 20 or more per unit area of 3.5 μm×3.5 μm, but it is not limited thereto.
An Al—Zn alloy of the present invention includes discontinuous precipitates or lamellar precipitates, wherein the discontinuous precipitates or the lamellar precipitates have an average length of 1.4 μm or more. If the average length of the discontinuous precipitates or the lamellar precipitates is less than 1.4 μm, it may be difficult to improve the tensile strength and the elongation of the Al—Zn alloy at the same time. The average length may be less than 1.4 μm per unit area of 3.5 μm×3.5 μm, but it is not limited thereto.
In the present invention, when an average spacing between the precipitates of the discontinuous precipitates or the lamellar precipitates is 105 nm or less, the tensile strength and the elongation of the Al—Zn alloy may be suitably improved at the same time. However, it is not limited thereto. For example, the average spacing between the precipitates may be 105 nm or less per unit area of 3.5 μm×3.5 μm.
In the present invention, when an average thickness of the discontinuous precipitates or the lamellar precipitates is 55 nm or less, the tensile strength and the elongation of the Al—Zn alloy may be suitably improved at the same time. However, it is not limited thereto. For example, the average thickness of the precipitates may be 55 nm or less per unit area of 3.5 μm×3.5 μm.
In the present invention, the discontinuous precipitates or the lamellar precipitates may be oriented. It may be suitable to improve the tensile strength and the elongation of an Al—Zn alloy at the same time by artificial orientation. The orientation of the aluminum-alloy according to the present invention may be achieved by plastic working. The plastic working may be selected from various processes such as drawing, rolling, and extrusion.
The discontinuous precipitates or the lamellar precipitates of an Al—Zn alloy of the present invention may be formed by subjecting the Al—Zn alloy to a heat treatment to form a solid solution, followed by an aging treatment. The production of the Al—Zn alloy will be described later in detail with reference to
A precipitation accelerating metal may be further added to promote the formation of precipitates during the production of the Al—Zn alloy of the present invention. The precipitation accelerating metal may be at least one chosen from copper (Cu), titanium (Ti), silicon (Si), iron (Fe), manganese (Mn), magnesium (Mg), and chromium (Cr).
The precipitating accelerating metal may be copper (Cu), and the copper may be included in an amount of 0.05 to 5 parts by weight based on the total weight of the alloy, but it is not limited thereto.
When the tensile strength of an Al—Zn alloy of the present invention is 300 MPa to 400 MPa, the elongation may be 10% or higher. In addition, when the tensile strength of an Al—Zn alloy of the present invention is 400 MPa to 500 MPa, the elongation may be 5% or higher. The Al—Zn alloy of the present invention may improve the tensile strength and the elongation at the same time.
Referring to
More specifically, zinc is included in an amount of more than 20 parts by weight and aluminum in an amount of 80 parts or less by weight based on the total weight of the Al—Zn alloy. The weight ratio of aluminum to zinc may be greater than 80:20 but less than 50:50, preferably greater than 70:30 and less than 50:50, and more preferably greater than 60:40 and less than 50:50.
At this time, the above precipitation accelerating metal may be selectively prepared. The precipitation accelerating metal may be as described above.
After the alloy material is prepared as described above, a solid solution is produced using the alloy material (S200). The step of producing a solid solution is a step for removing residual precipitates. If the precipitating accelerating metal is included in the step of preparing the alloy material (S100), the solid solubility may be lowered.
The solid solution may be formed by heat-treating the alloy. The heat treatment may be a homogenization treatment and/or a solubilization treatment. Due to the formation of the solid solution, the Al—Zn alloy becomes a state including the solid solution.
A temperature range of the step of producing a solid solution may be from 350 to 450° C. The temperature range may be determined by taking into account the maximum solid solution-limit temperature at which an Al—Zn alloy does not form a liquid phase and forms a solid solution. The Al—Zn alloy does not form discontinuous precipitates because it forms a polyphase without forming a single phase at a temperature of higher than 450° C. The step of producing a solid solution may be performed by heating for 30 minutes or more.
The discontinuous precipitates are forcibly formed using the Al—Zn alloy including the solid solution (S300).
The step of forcibly producing the precipitates is producing discontinuous precipitates or lamellar precipitates within the alloy, which comprises aging the aluminum-alloy including the solid solution to form 5% or more of discontinuous precipitates or lamellar precipitates per unit area.
The aging treatment may be performed at a temperature of 120 to 200° C. which is lower than the step of forming the solid solution may. For example, the aging treatment may be performed at 160° C. The aging treatment may be performed for 5 minutes to 400 minutes. For example, in the case where the alloy material includes a precipitation accelerating metal, water quenching or air quenching may be performed after producing the solid solution, and the aging treatment may be performed for at least 2 hours forcibly to produce discontinuous precipitates, while the aging treatment may be performed for at least 5 hours in the case where the alloy material does not include a precipitation accelerating metal.
As described above, the water quenching or the air quenching before the aging treatment may form oriented precipitates later by rapidly quenching the temperature lowering speed. If the temperature is slowed down by slowing down the temperature lowering speed, these precipitates may not be oriented even if they are forced to produce discontinuous precipitates or lamellar precipitates.
After forcibly forming the discontinuous precipitates or the lamellar precipitates as described above, the Al—Zn alloy including the precipitates is calcined to form oriented precipitates (S400).
The step for orienting to form oriented precipitates is a process of artificially orienting the forcibly formed discontinuous precipitates, which may be performed by rolling, drawing and/or extruding. A drawing ratio, which is a reduction rate of a cross-sectional area, may be 50% or more. As the draw ratio increases, the distance between the oriented precipitates and the thickness of the oriented precipitates themselves may decrease, and the tensile strength may be improved
The orientation step may be performed in a liquid nitrogen atmosphere. When oriented in a liquid nitrogen atmosphere, the heat generated in the orientation step may be minimized, facilitating the orientation of the discontinuous precipitates, resulting in increased tensile strength.
As described above, the Al—Zn alloy of the present invention forcibly forms discontinuous precipitates or lamellar precipitates during the manufacturing process, and includes the oriented precipitates formed by using the same, whereby the tensile strength and the elongation are simultaneously improved (See
Hereinafter, the present invention will be described in more detail with reference to specific production examples and comparative examples of the present invention along with the results of the characteristics evaluation thereof.
Table 1 shows contents of Examples and Comparative Examples of an Al—Zn alloy of the present invention.
The Al—Zn alloy of Table 1 was casted by electric furnace melting and high-frequency induction melting. A homogenization treatment was performed at 370° C. for 30 hours in order to remove impurities generated during casting. Subsequently, heat treatment was performed at a reduction rate of 20% at 400° C. every 15 minutes to perform swaging at a total cold working area reduction rate of 75%. After 1 hour had elapsed, the resultant solution was subjected to solution treatment at 400° C. for 1 hour and then water-quenched. It was then subjected to precipitation treatment to produce discontinuous precipitates at 160° C.
Analysis of Changes in an Area Ratio of Precipitates
For each of Examples and Comparative Examples, an area ratio (fraction (%)) of the discontinuous precipitates was measured during the heat treatment at 160° C. as an aging treatment, and the results are shown in
Referring to
Referring to
Analysis of Morpholoqical Chancres of Precipitates
Referring to
Referring to
Referring to
Time Dependence Analysis of Aging Process
Structures of the precipitates are shown in
Analysis of Chancres in Tensile Strength and Elongation According to Drawing Ratio
Analysis of Properties According to Drawing Conditions
Analysis of Discontinuous Precipitate Properties according to Cu Addition
Analysis of Tensile Strength and Elongation After Drawing
Referring to
Table 2 shows processing rate, tensile strength and elongation of the Al—Zn alloy according to Examples of the present invention.
The spirit of the present disclosure has been described by way of example hereinabove, and the present disclosure may be variously modified, altered, and substituted by those skilled in the art to which the present disclosure pertains without departing from essential features of the present disclosure. Accordingly, the exemplary embodiments disclosed in the present disclosure and the accompanying drawings do not limit but describe the spirit of the present disclosure, and the scope of the present disclosure is not limited by the exemplary embodiments and accompanying drawings. The scope of the present disclosure should be interpreted by the following claims and it should be interpreted that all spirits equivalent to the following claims fall within the scope of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2016-0071883 | Jun 2016 | KR | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 3676115 | Hare | Jul 1972 | A |
| 20180298474 | Han | Oct 2018 | A1 |
| Number | Date | Country |
|---|---|---|
| 2000-096166 | Apr 2000 | JP |
| 10-1274063 | Jun 2013 | KR |
| 10-2017-0014282 | Feb 2017 | KR |
| Entry |
|---|
| Japanese Office Action dated Apr. 20, 2018, issued in corresponding Japanese Patent Application No. 2017-111175. |
| Shiming Hao et al., “Effect of Cu on Discontinuous Precipitation of a Symmetrical AlZn Alloy”, J. Mater. Sci Technol., vol. 21 No. 2, 2005, 215-218 pages. |
| Number | Date | Country | |
|---|---|---|---|
| 20170356072 A1 | Dec 2017 | US |
