Patent Application
20200102631
The present invention belongs to the metal materials and metallurgical field, and specifically relates to a wrought Mg-RE alloy and a method for obtaining a magnesium alloy with excellent overall performances by adjusting the contents of alloy elements (Gd, Y and Zn) or modifying hot working processes.
As the magnesium alloy has many advantages, such as low density, high specific strength, high specific stiffness, excellent damping performance and good castability, a boom in the development and application of the magnesium alloy has been started in the world since 1990s. The magnesium alloy has a wide prospect of application in aerospace, automobile, high-speed rail, and 3C fields. However, the absolute strength of the magnesium alloy is low, and the plasticity, flame retardant property and corrosion resistance are poor, which limits the large-scale application of the magnesium alloy. Therefore, it becomes particularly important to develop a magnesium alloy with excellent overall performances.
The rare-earth containing magnesium alloys have excellent room-temperature mechanical properties and heat resistance. Kawamura et al. prepared an ultra-high strength Mg97Zn1Y2 alloy with the room-temperature yield strength greater than 600 MPa by employing rapid solidification and powder metallurgy technology, however, the complicated and dangerous preparing process greatly increases the preparation difficulty and cost, which limits the wide application of the alloy. Homma et al. prepared a rare-earth containing magnesium alloy with excellent mechanical properties by employing conventional casting, extrusion and heat treatment processes, the tensile strength and yield strength thereof at room temperature are 542 MPa and 473 MPa, respectively, and the elongation thereof is 8%. However, the rare-earth content in this alloy reaches up to 16 wt. %, and it not only increases the material cost, but also increases the density of the alloy, which weakens the advantage of the magnesium alloy as a light material. Jian et al. added 1.8 wt. % Ag into Mg—Gd—Y—Zr alloy prior to rolling deformation, and the room-temperature tensile strength and yield strength of the alloy reached 600 MPa and 575 MPa, respectively, meanwhile, it has a elongation of 5.2%. However, the addition of Ag in a high content results in a significant increase in the material cost, while the corrosion resistance of the alloy is also decreased, which is not beneficial for the practical application of the magnesium alloy. In addition, as compared with other common metal materials, the magnesium alloys generally have a lower ignition point. Such a relative strong inflammability hinders the applications of magnesium alloys in many fields, especially in aerospace field. It also requires more intensive researches in the corrosion resistance.
The patent application No. CN201110282459.1 discloses a magnesium alloy with high toughness and high yield strength. After homogenization treatment, extrusion and aging treatment, the tensile strength of the alloy can reach to 360 MPa, the yield strength can reach to 330 MPa, and the elongation can reach to 11%. The patent application No. CN201110340198.4 discloses a high-strength and heat-resistant magnesium alloy with low rare earth content and its preparation method”. After homogenization treatment, extrusion and aging treatment, the alloy exhibits a tensile strength≥250 MPa, and an elongation≥8%. The patent application No. CN200510025251.6 discloses a high-strength and heat-resistant magnesium alloy and its preparation method. The magnesium alloy in T5 state can exhibit a tensile strength≥369 MPa, a yield strength≥288 MPa, and an elongation≥5.1%. The mechanical properties of the rare-earth containing magnesium alloys involved in the above patents are relatively low, and it is difficult to apply them in bearing components in a large amount.
The patent application No. CN201210164316.5 discloses a high-strength Mg—Gd—Y—Zn—Mn alloy. After homogenization treatment, extrusion and heat treatment, the alloy can exhibit a tensile strength≥428 MPa, a yield strength≥241 MPa, and an elongation≥7.7%. The patent application No. CN201410519516.7 discloses preparation and treatment processes of a Mg—Gd—Y—Zr alloy. After T5 treatment, the highest mechanical properties thereof are: a tensile strength of 403 MPa, a yield strength of 372 MPa, and an elongation of 4.4%. The patent application No. CN201610122639.6 discloses a Mg—Gd—Y—Ni—Mn alloy with high strength and high plasticity and its preparation method. Its highest mechanical properties can reach to a tensile strength≥450 MPa, and an elongation≥9.0%, but the rare-earth content of the alloys listed in this patent are about 12%, leading to a high cost. The rare-earth content of the alloys involved in the above patents are all high, resulting in increasing cost and density of the alloys, which is not beneficial for the widely industrial applications.
The patent application No. CN201010130610.5 discloses a flame-retardant magnesium alloy containing Gd, Er, Mn and Zr, wherein its flame retardant temperature can reach to 740° C., the room-temperature tensile strength of the cast alloy can reach to 220 MPa, and the elongation is larger than 5%. The patent application No. CN201210167350.8 discloses a flame-retardant magnesium alloy, wherein the elements such as Ca, Sr, RE, and Be are added into AZ91D alloy, such that the ignition point of the material is increased to 710° C. The patent application No. CN201410251364.7 discloses a flame-retardant and high-strength magnesium alloy and its preparation method, wherein the alloy has a composition of Mg—Al—Y—CaO, a flame retardant temperature≥745° C., and a room-temperature tensile strength≥231 MPa. These alloys involved in the above patents have a good flame retardant property, but poor mechanical properties, which limits its application and development.
The corrosion resistance of the alloy has a crucial influence on its application.
The corrosion resistance of the current commercial magnesium alloys is poor, and the corrosion rate of AZ31 magnesium alloy is about 4.5 mg·cm−2·d−1. In the patent application No. CN201010120418.8, the corrosion rate thereof can be reduced to as low as 0.98 mg·cm−2·d−1 by adding Y-rich mischmetal into AZ31. The corrosion rate of AZ91 alloy is about 1.58 mg·cm−2·d−1. The patent application No. CN200910248685.0 discloses a magnesium alloy with corrosion resistance, wherein the corrosion rate thereof is remarkably reduced to as low as 0.64 mg·cm−2·d−1 by adding a certain amount of Cd into AZ91. The patent application No. CN201410521001.0 discloses a magnesium alloy with corrosion resistance, wherein the corrosion rate thereof can reach to as low as 0.54 mg·cm−2·d−1 by adding V element into AZ91. The corrosion rate of the rare-earth containing magnesium alloy is lower, and the corrosion rate of WE43 alloy is about 0.6 mg·cm−2·d−1. The patent application No. CN200910099330.X discloses a Mg—Nd—Gd—Zn—Zr alloy with CaO added therein, wherein the corrosion rate thereof can be as low as 0.16 mg·cm−2·d−1, but after T6 treatment, the strength thereof is poor, and the high cost also limits its application and development.
Furthermore, the fracture toughness of the magnesium alloy are generally low, so it is of important significance to develop a magnesium alloy with high fracture toughness for improving the security and reliability during the service of the magnesium alloys.
As a metallic structural material having a wide application prospect, the magnesium alloy still faces a lot of technical problems urgent to be solved in the practical application. In order to promote the application of the magnesium alloy, there is a need to develop alloys with good overall performances while ensuring the acceptable material cost.
In order to overcome the problem of overhigh rare earth content and insufficient overall performance of the current high-strength magnesium alloy, the present invention develops Mg—Gd—Y—Zn—Zr alloys with low rare-earth content and high strength, high toughness, and excellent anti-flammability and corrosion resistance, and a process for preparing the same. The total content of rare earth is not more than 11 wt. %, and the process is simple, the operation is easy, and the cost is low, so that the problem of complicated preparation process and high preparation cost for the alloy is overcome.
The object of the present invention is achieved by the technical solutions as follows.
A Mg—Gd—Y—Zn—Zr alloy with high strength and toughness, corrosion resistance and anti-flammability, wherein the components and the mass percentages thereof in the alloy are: 3.0%≤Gd≤9.0%, 1.0%≤Y≤6.0%, Gd+Y≤11.0%, 0.5%≤Zn≤3.0%, 0.2%≤Zr≤1.5%, and the balance being Mg and inevitable impurities.
A process for preparing the aforementioned Mg—Gd—Y—Zn—Zr alloy with high strength and toughness, corrosion resistance and anti-flammability, specifically carried out by steps of:
(1) calculating and burdening according to the alloy composition, wherein the raw materials Gd, Y and Zr are added in the form of master alloys of Mg-30 wt. % Gd, Mg-30 wt. % Y and Mg-30 wt. % Zr, respectively, and Mg and Zn are added in the form of industrially pure Mg and pure Zn, respectively;
(2) increasing the temperature of a smelting furnace to 760-850° C., adding the pure Mg and pure Zn prepared in step 1 into the smelting furnace under the protection of mixed gases of CO2+10 vol % SF6;
(3) reducing the temperature of the furnace to 730-780° C. after the pure Mg and pure Zn added in step (2) are completely melted, adding the Mg—Gd master alloy, the Mg-Y master alloy, and the Mg—Zr master alloy in this order, to obtain a melt;
(4) adjusting the temperature of the furnace to 700-750° C., removing the slag on the surface of the melt, refining the melt for 10-20 minutes by introducing preheated argon at the bottom of the furnace, to improve the purity of the melt;
(5) increasing the temperature to 730-760° C., transferring the melt into a holding furnace under the pressure of 0.01 to 0.02 MPa, and holding for 1-3 hours; and
(6) reducing the temperature to 700-720° C., casting the melt prepared in step (5) at a rate of 42 mm/min, cooling and crystalizing the cast ingot with cooling water at room temperature and a pressure of 0.02 MPa, to finally obtain a large ingot of the Mg—Gd—Y—Zn—Zr alloy with a diameter of 170 mm and a length≥2.5 m by casting;
(7) conducting a homogenization treatment on the ingot at a temperature of 450-550° C. for 8-24 hours, and then quenching in warm water at 50-80° C.;
(8) conducting an indirect extrusion on the ingot after the homogenization treatment, wherein the extrusion temperature is controlled at 350-450° C., the extrusion ratio is 8-20, and the rain speed is 0.05-5 mm/s; and
(9) conducting an isothermal aging treatment on the extruded alloy at 175-225° C. for a holding time of 0.5-200 hours, quenching and cooling the sample in warm water at 50-80° C. after the aging treatment, to obtain the target alloy.
The present invention has the following beneficial effects.
1. The present invention can produce a magnesium alloy with high strength and toughness and low rare earth content by employing conventional preparation processes. The extrusion process is simple and easy to operate, and has a wide application range.
2. The Mg—Gd—Y—Zn—Zr alloy not only has excellently high strength and toughness, but also has excellent corrosion resistance and flame retardant property. As compared with the commonly used commercial magnesium alloys such as AZ91, ZK60 and WE43, the overall performance thereof has a significant improvement.
3. When the total amount of rare earth in the Mg—Gd—Y—Zn—Zr alloys is 7-11 wt %, the alloy has a tensile strength≥428 MPa, a yield strength≥409 MPa, an elongation≥10.1%, a fracture toughness (Kq value)≥21.3 MPa·m1/2, a corrosion rate in the salt spray test (3.5% NaCl)≤0.56 mg·cm−2·d−1, and an ignition point≥708° C.
4. Both the fracture toughness and the corrosion resistance of the Mg—Gd—Y—Zn—Zr alloy are better than those of WE43 alloy, while the flame retardant property thereof is equivalent to that of WE43 alloy.
The technical solution of the present invention will be further described below by referring to the Examples. However, the present invention is not limited thereto, and any modifications or equivalent alternatives of the technical solution of the present invention, without departing from the spirit and scope of the technical solution of the present invention, should be included in the scope of the present invention.
In the Example, the components and the mass percentages thereof contained in the Mg—Gd—Y—Zn—Zr alloy with high strength are: Gd 8.0%, Y 3.0%, Zn 1.0%, Zr 0.5%, and the balance being Mg and inevitable impurity elements. The specific preparation method for the alloy is carried out according to the following steps:
1. weighing pure Mg, pure Zn, Mg—Y master alloy, Mg—Gd master alloy and Mg—Zr master alloy according to the ratio of 8% Gd, 3% Y, 1% Zn, 0.5% Zr and the balance of Mg based on mass percentage;
2. heating the smelting furnace to 800° C., adding the pure Mg and pure Zn prepared in step 1 into the smelting furnace under the protection of mixed gases of CO2+10 vol % SF6;
3. reducing the temperature of the furnace to 760° C. after the pure Mg and pure Zn are completely melted, adding the Mg—Gd master alloy, the Mg—Y master alloy, and the Mg—Zr master alloy in this order, to obtain a melt;
4. reducing the furnace temperature to 740° C., removing the slag on the surface of the melt, refining the melt for 15 minutes by introducing preheated argon at the bottom of the furnace, to improve the purity of the melt;
5. increasing the temperature to 750° C., transferring the melt into a holding furnace under a pressure of 0.02 MPa, and holding for 2 hours,
6. reducing the temperature to 705° C., casting the melt prepared in step 5 at a rate of 42 mm/min, cooling and crystalizing the cast ingot with cooling water at room temperature and a pressure of 0.02 MPa, to finally obtain a large ingot of the Mg—Gd—Y—Zn—Zr alloy with a diameter of 170 mm and a length of 2.75 m by casting;
7. conducting a homogenization treatment on the ingot at 500° C. for 12 hours, then quenching in warm water at 80° C.;
8. conducting an indirect extrusion on the ingot after the homogenization treatment, wherein the extrusion temperature is controlled at 390° C., the extrusion ratio is 12:1, and the rain speed is 0.1 mm/s; and
9. conducting an isothermal aging treatment on the extruded alloy at 200° C. for 72 hours, and quenching the sample in warm water at 80° C. after the aging treatment, to obtain the target alloy.
The resultant alloy of the Example has a tensile strength of 465 MPa, a yield strength of 437 MPa, and an elongation of 10.8%. See Table 1 for details.
In the Example, the components and the mass percentages thereof contained in the Mg—Gd—Y—Zn—Zr alloy with high strength are: Gd 8.4%, Y 2.4%, Zn 0.6%, Zr 0.4%, and the balance being Mg and inevitable impurity elements. The preparation method of the Mg—Gd—Y—Zn—Zr alloy with high strength is: firstly, weighing pure Mg, pure Zn, Mg—Y master alloy, Mg—Gd master alloy and Mg—Zr master alloy according to the ratio of 8.4% Gd, 2.4% Y, 0.6% Zn, 0.4% Zr and the balance of Mg based on mass percentage; casting the alloy according to steps 2-6 in Example 1; conducting the homogenization treatment on the ingot at 500° C. for 12 hours, then quenching in the warm water at about 80° C.; conducting the indirect extrusion on the ingot after the homogenization treatment, wherein the extrusion temperature is controlled at 400° C., the extrusion ratio is 12:1, and the rain speed is 0.1 mm/s; conducting the isothermal aging treatment on the extruded alloy at 200° C. for 118 hours, and quenching the sample in the warm water at 80° C. after the aging treatment, to obtain the target alloy. The properties of the alloy are shown in Table 1.
In the Example, the components and the mass percentages thereof contained in the Mg—Gd—Y—Zn—Zr alloy with high strength are: Gd 6.7%, Y 1.3%, Zn 0.6%, Zr: 0.5%, and the balance being Mg and inevitable impurity elements. The preparation method of the Mg—Gd—Y—Zn—Zr alloy with high strength is: firstly, weighing pure Mg, pure Zn, Mg—Y master alloy, Mg—Gd master alloy and Mg—Zr master alloy according to the ratio of 6.7% Gd, 1.3% Y, 0.6% Zn, 0.5% Zr and the balance of Mg based on mass percentage; casting the alloy according to steps 2-6 in Example 1; conducting the homogenization treatment on the ingot at 510° C. for 8 hours, then quenching in the warm water at about 80° C.; conducting the indirect extrusion on the ingot after the homogenization treatment, wherein the extrusion temperature is controlled at 400° C., the extrusion ratio is 12:1, and the ram speed is 0.1 mm/s; conducting the isothermal aging treatment on the extruded alloy at 200° C. for 84 hours, and quenching the sample in the warm water at 80° C. after the aging treatment, to obtain the target alloy. The properties of the alloy are shown in Table 1.
In the Example, the components and the mass percentages thereof contained in the Mg—Gd—Y—Zn—Zr alloy with high strength are: Gd 8.4%, Y 0.8%, Zn 0.7%, Zr 0.6%, and the balance being Mg and inevitable impurity elements. The preparation method of the Mg—Gd—Y—Zn—Zr alloy with high strength is: firstly, weighing pure Mg, pure Zn, Mg—Y master alloy, Mg—Gd master alloy and Mg—Zr master alloy according to the ratio of 8.4% Gd, 0.8% Y, 0.7% Zn, 0.6% Zr and the balance of Mg based on mass percentage; casting the alloy according to steps 2-6 in Example 1; conducting the homogenization treatment on the ingot at 510° C. for 8 hours, then quenching in the warm water at about 80° C.; conducting the indirect extrusion on the ingot after the homogenization treatment, wherein the extrusion temperature is controlled at 400° C., the extrusion ratio is 12:1, and the ram speed is 0.1 mm/s; conducting the isothermal aging treatment on the extruded alloy at 200° C. for 84 hours, and quenching the sample in the warm water at 80° C. after the aging treatment, to obtain the target alloy. The properties of the alloy are shown in Table 1.
In the Example, the components and the mass percentages thereof contained in the Mg—Gd—Y—Zn—Zr alloy with high strength are: Gd 7.1%, Y 2.0%, Zn 1.1%, Zr 0.5%, and the balance being Mg and inevitable impurity elements. The preparation method of the Mg—Gd—Y—Zn—Zr alloy with high strength is: firstly, weighing pure Mg, pure Zn, Mg—Y master alloy, Mg—Gd master alloy and Mg—Zr master alloy according to the ratio of 7.1% Gd, 2.0% Y, 1.1% Zn, 0.5% Zr and the balance of Mg based on mass percentage; casting the alloy according to steps 2-6 in Example 1; conducting the homogenization treatment on the ingot at 510° C. for 8 hours, then quenching in the warm water at about 80° C.; conducting the indirect extrusion on the ingot after the homogenization treatment, wherein the extrusion temperature is controlled at 400° C., the extrusion ratio is 12:1, and the ram speed is 0.1 mm/s; conducting the isothermal aging treatment on the extruded alloy at 200° C. for 84 hours, and quenching the sample in the warm water at 80° C. after the aging treatment, to obtain the target alloy. The properties of the alloy are shown in Table 1.
The present invention obtains a wrought magnesium alloy having superior overall performances with a small amount of rare earth element by adjusting the proportion of the alloy elements and by conventional casting, extrusion and heat treatment processes. At room-temperature, the tensile strength thereof is 428-465 MPa, the yield strength is 409-437 MPa, and the elongation is 10.1%-14.4%; meanwhile, it also has excellent fracture toughness, corrosion resistance and flame retardant property. The cost of the alloy is reduced while the strength of the alloy is maintained.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201611133731.9 | Dec 2016 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2017/114605 | 12/5/2017 | WO | 00 |
