CN100441718C - In Situ Synthesis of Quasicrystals and Their Approximate Phases Reinforced Heat-resistant Magnesium Alloys - Google Patents

Abstract

An in-situ synthesized quasicrystal and its approximate phase-reinforced heat-resistant magnesium alloy, the components and their weight percentages are: 5-10% Zn, 1-5% Cu, 2-6% Gd, impurity element Fe<0.005%, Ni<0.002%, the rest is Mg. The alloy of the present invention has a special strengthening phase—quasicrystal and its approximate phases, which surround the matrix with a skeleton structure to strengthen; at the same time, through the aging treatment process, the matrix precipitates MgZn phase, thereby further enhancing the mechanical properties of the alloy performance. The alloy of the invention has excellent heat-resistant performance, and its creep performance (under the condition of 200 DEG C and 50MPa tensile creep) is 1-2 order of magnitude higher than that of the AE42 heat-resistant magnesium alloy. The high-performance heat-resistant magnesium alloy of the invention will greatly increase the application temperature range of the magnesium alloy.

Description

In Situ Synthesis of Quasicrystals and Their Approximate Phases Reinforced Heat-resistant Magnesium Alloys

technical field

The invention relates to a high-performance heat-resistant magnesium alloy, in particular to an in-situ synthesized quasi-crystal and its approximate phase-enhanced heat-resistant magnesium alloy. It belongs to the field of metal materials.

Background technique

The current application of magnesium alloy structural parts in automobiles is limited to accessories such as instrument panels, steering wheels, valve covers, etc., and the application of parts working at higher temperatures (120°C-200°C) is still very limited, and the high-temperature mechanical properties of magnesium alloys are poor. It is a key factor hindering its application in the automotive industry. Existing commercial magnesium alloys such as AM and AZ series have a certain yield strength at room temperature, but the creep strength in the temperature range of 120°C-200°C is very low, less than 20Mpa, which cannot meet the requirements of high-temperature automotive parts. Application performance requirements. The fundamental reason for the low creep performance of Mg-Al-based alloys is that the strengthening phase in the matrix is Mg ₁₇ Al ₁₂ phase, which precipitates in a discontinuous form at the grain boundary. Since the melting point of this phase is only 437°C, the atomic The intensification of diffusion leads to its easy softening and coarsening, thus losing its strengthening effect on the matrix. Quasicrystals are a new form of matter different from crystals, which have special rotational symmetries such as five times and ten times. Due to the unique atomic structure of quasicrystals, quasicrystals have special physical and mechanical properties. Studies have shown that quasicrystals have high compressive strength, high microhardness and elastic modulus, low thermal expansion coefficient and surface tension, etc. At the same time, the stable quasicrystals formed during solidification also have high heat resistance and resistance corrosion and wear resistance properties. In view of the above-mentioned characteristics of quasicrystals, recent efforts have been made to introduce quasicrystal particles as a second phase to strengthen Mg alloys and improve the mechanical properties of magnesium alloys.

After searching the literature of the prior art, it was found that the U.S. Patent Application No.: 20030029526, the patent name is: Quasicrystalline phase-reinforced Mg-based metallic alloy with high warmth and hot formability and method of making the same (quasicrystalline phase-reinforced Mg-based metallic alloy with high warmth and hot formability and method of making the same Magnesium-based alloy and its preparation method), the patent is a quasi-crystalline reinforced Mg-Zn-Y ternary alloy with good thermal deformation ability, and its alloy composition is 1-10at%Zn, 0.1-3at%Y, The balance is Mg. The alloy provides mechanical properties at room temperature, but does not provide high-temperature mechanical properties, and is mainly used as a deformed magnesium alloy. After the alloy is cast, further thermal deformation processing is required, and it cannot be directly used for casting automobile engines and other working temperature requirements ( 120°C-200°C) parts.

Contents of the invention

The purpose of the present invention is to overcome the defect of low creep performance of existing heat-resistant magnesium alloys, and provide an in-situ synthesized quasicrystal and its approximate phase-enhanced heat-resistant magnesium alloy, which can introduce a new strengthening phase into the magnesium matrix -Quasicrystals and their approximate phases can greatly improve the high temperature creep performance of magnesium alloys, thereby greatly improving the application range of magnesium alloys in the automotive industry.

The present invention is achieved through the following technical solutions, the components of the present invention and their weight percentages are: 5-10% Zn, 1-5% Cu, 2-6% Gd, impurity elements Fe<0.005%, Ni<0.002% , and the rest are Mg.

According to the performance-price ratio of the alloy, the components of the present invention and their weight percentages are further limited to: 6-8% Zn, 2-4% Cu, 3-5% Gd, impurity elements Fe<0.005%, Ni<0.002%, The rest is Mg. Taking the Mg-7Zn-3Cu-4Gd alloy as an example, the compressive strength and compressive elongation at room temperature reach 486MPa and 17%, respectively. High-temperature tensile creep performance under the conditions of 200°C and 50MPa: the steady-state creep rate is 5.7×10 ^-8 %/S, and the creep strain after 100 hours is 0.17%. Under the same conditions, the steady-state creep rate of commercial heat-resistant magnesium alloy AE42 is 4.2×10 ^-6 %/S, and the creep strain after 100 hours is 2.67%. The high-temperature creep performance of the inventive alloy is 1-2 orders of magnitude higher than that of AE42 (a benchmark alloy for evaluating the heat-resistant performance of magnesium alloys at present).

The magnesium alloy of the present invention is prepared by the following process:

(1) Ingredients: Raw materials such as high-purity magnesium, high-purity zinc, high-purity copper, and magnesium-gadolinium intermediate alloy are mixed according to the mass percentage of the formula.

(2) Smelting: Before smelting, dry all ingredients at about 200°C for 1 hour, then put them into a conventional resistance furnace (intermediate frequency induction furnace), and smelt under flux (gas) protection melting conditions.

(3) Casting: The molten metal is poured into the mold to obtain the casting. The casting method can be sand casting, low pressure casting, metal casting or die casting.

(4) Aging treatment: heat the casting to a certain temperature in the range of 100-400°C or several temperatures for 0.2-72 hours, and then cool to obtain the finished product.

The invention contains a special strengthening phase-quasicrystal and its approximate phase. The obtained quasicrystal and its approximate phase structure have a closed skeleton morphology structure, which can well strengthen the magnesium matrix; at the same time, the obtained The quasicrystal and its approximate phases have high thermal stability, and the high temperature strengthening effect can be maintained above 200 °C. By performing an aging treatment process on the material of the invention, the MgZn strengthening phase is precipitated in the matrix, which can further strengthen the matrix and improve the mechanical properties of the magnesium alloy.

Compared with the background technology, the present invention has outstanding substantive features and significant progress. The present invention is a quaternary alloy component based on Mg-Zn-Cu-Gd that can synthesize quasicrystals and their approximate phases in situ. In addition to good mechanical properties at room temperature, the alloy especially has excellent high temperature creep resistance. The minimum steady-state creep rate under 200°C and 50Mpa tensile creep conditions is 5.2× ^10-8 %/S, and the creep strain after 100 hours is 0.15%; while the steady-state creep rate of AE42 magnesium alloy under the same conditions The rate is 4.2×10 ^-6 %/S, and the creep strain after 100 hours is 2.67%. That is, the high-temperature creep resistance of the new alloy of the present invention is nearly 2 orders of magnitude higher than that of the AE42 heat-resistant magnesium alloy (the current benchmark alloy for evaluating the heat-resistant performance of magnesium alloys). Moreover, because it is a magnesium alloy for casting, it does not require thermal deformation processing, and can be directly used for casting automotive engines and other parts with high operating temperature requirements (120°C-200°C), and the preparation process is simpler.

Detailed ways

Provide following embodiment in conjunction with content of the present invention:

Example 1:

Alloy composition weight percent: 5.0% Zn, 1% Cu, 2% Gd, impurity elements Fe≤0.005%, Ni≤0.002%, and the rest is Mg.

Configure the alloy according to the above ingredients, add 8.6Kg of industrial pure magnesium, 0.1Kg of industrial pure copper, 0.5Kg of industrial pure zinc, and 0.8Kg of Mg-25Gd master alloy in the resistance furnace, smelt under the protection of gas (or solvent), and treat the alloy elements After it is completely dissolved, continue to raise the temperature to 720°C-740°C, then keep it warm for 30 minutes, remove the scum on the surface, and then use the ladle for sand casting. During the casting process, pass protective gas above the melt for protection. The normal-temperature compressive strength and compressive elongation of the alloy of the invention reach 408MPa and 18% respectively. High-temperature tensile creep performance under the conditions of 200°C and 50MPa: the steady-state creep rate is 3.1×10 ^-7 %/S, and the creep strain after 100 hours is 0.30%. Under the same conditions, the steady-state creep rate of commercial heat-resistant magnesium alloy AE42 is 4.2×10 ^-6 %/S, and the creep strain after 100 hours is 2.67%. The high-temperature creep performance of the inventive alloy is improved by an order of magnitude compared with AE42.

Example 2:

Alloy composition weight percent: 6.0% Zn, 2% Cu, 3% Gd, impurity element Fe≤0.005%, Ni≤0.002%, and the rest is Mg.

Configure the alloy according to the above ingredients, add 8Kg of industrial pure magnesium, 0.2Kg of industrial pure copper, 0.6Kg of industrial pure zinc, and 1.2Kg of Mg-25Gd master alloy into the intermediate frequency induction furnace, and melt under the protection of gas. After all the alloy elements are dissolved, Continue to raise the temperature to 720°C-740°C, then keep it warm for 10 minutes, remove the scum on the surface, and then cast the metal mold. The normal-temperature compressive strength and compressive elongation of the alloy of the invention reach 438MPa and 18% respectively. High-temperature tensile creep performance under the conditions of 200°C and 50MPa: the steady-state creep rate is 9.1×10 ^-8 %/S, and the creep strain after 100 hours is 0.25%. Under the same conditions, the steady-state creep rate of commercial heat-resistant magnesium alloy AE42 is 4.2×10 ^-6 %/S, and the creep strain after 100 hours is 2.67%. The high-temperature creep performance of the inventive alloy is more than one order of magnitude higher than that of AE42.

Example 3:

Alloy composition weight percent: 7.0% Zn, 3% Cu, 4% Gd, impurity element Fe≤0.005%, Ni≤0.002%, and the rest is Mg.

Configure the alloy according to the above ingredients, add 7.4Kg of industrial pure magnesium, 0.3Kg of industrial pure copper, 0.7Kg of industrial pure zinc, and 1.6Kg of Mg-25Gd master alloy into the intermediate frequency induction furnace, melt under the protection of gas, and wait until all the alloy elements are dissolved , continue to raise the temperature to 720°C-740°C, then keep the heat and let it stand for 10 minutes, remove the surface scum and carry out low-pressure casting in a low-pressure casting furnace using nitrogen gas pressure. The normal temperature compressive strength and compressive elongation of the alloy of the invention reach 486MPa and 17% respectively. High-temperature tensile creep performance under the conditions of 200°C and 50MPa: the steady-state creep rate is 5.7×10 ^-8 %/S, and the creep strain after 100 hours is 0.17%. Under the same conditions, the steady-state creep rate of commercial heat-resistant magnesium alloy AE42 is 4.2×10 ^-6 %/S, and the creep strain after 100 hours is 2.67%. The high-temperature creep performance of the inventive alloy is 1-2 orders of magnitude higher than that of AE42.

Example 4:

Alloy composition weight percent: 8.0% Zn, 4% Cu, 5% Gd, impurity element Fe≤0.005%, Ni≤0.002%, and the rest is Mg.

Configure the alloy according to the above ingredients, add 6.8Kg of industrial pure magnesium, 0.4Kg of industrial pure copper, 0.8Kg of industrial pure zinc, and 2.0Kg of Mg-25Gd master alloy into the intermediate frequency induction furnace, melt under the protection of gas, and wait until all the alloy elements are dissolved , continue to raise the temperature to 720°C-740°C, then keep it warm for 10 minutes, remove the scum on the surface, and then carry out metal mold casting. The normal temperature compressive strength and compressive elongation of the alloy of the invention reach 480MPa and 16% respectively. High-temperature tensile creep performance under the conditions of 200°C and 50MPa: the steady-state creep rate is 5.4×10 ^-8 %/S, and the creep strain after 100 hours is 0.16%. Under the same conditions, the steady-state creep rate of commercial heat-resistant magnesium alloy AE42 is 4.2×10 ^-6 %/S, and the creep strain after 100 hours is 2.67%. The high-temperature creep performance of the inventive alloy is 1-2 orders of magnitude higher than that of AE42.

Example 5:

Alloy composition weight percent: 10.0% Zn, 5% Cu, 6% Gd, impurity element Fe≤0.005%, Ni≤0.002%, and the rest is Mg.

Configure the alloy according to the above ingredients, add 6.1Kg of industrial pure magnesium, 0.5Kg of industrial pure copper, 1.0Kg of industrial pure zinc, and 2.4Kg of Mg-25Gd master alloy into the intermediate frequency induction furnace, melt under the protection of gas, and wait until all the alloying elements are dissolved , continue to raise the temperature to 720°C-740°C, then keep it warm for 20 minutes, remove the scum on the surface, and then cast the metal mold. The normal temperature compressive strength and compressive elongation of the alloy of the invention reach 450MPa and 11% respectively. High-temperature tensile creep performance at 200°C and 50MPa: the minimum steady-state creep rate is 5.2×10 ^-8 %/S, and the creep strain after 100 hours is 0.15%. However, under the same conditions, the steady-state creep rate of AE42 magnesium alloy is 4.2×10 ^-6 %/S, and the creep strain after 100 hours is 2.67%. The high-temperature creep performance of the inventive alloy is nearly 2 orders of magnitude higher than that of AE42.

Among the above five examples, the alloys in examples 2, 3, and 4 have better overall performance-price ratios. The alloy in Example 3 not only has the best compressive strength, but also has excellent high-temperature creep properties. In addition, compared with Examples 4 and 5, Example 3 contains a lower content of Gd, and the cost of the alloy is relatively low, so it has the best overall performance-price ratio.

Claims (2)

1. An in-situ synthesized quasicrystal and its approximate phase-reinforced heat-resistant magnesium alloy, characterized in that the components and their weight percentages are: 5-10% Zn, 1-5% Cu, 2-6% Gd, impurities Element Fe<0.005%, Ni<0.002%, and the rest is Mg. 2. The in-situ synthesized quasicrystal and its approximate phase-reinforced heat-resistant magnesium alloy according to claim 1, characterized in that its weight percentage is further limited to: 6-8% Zn, 2-4% Cu, 3- 5% Gd, impurity element Fe<0.005%, Ni<0.002%, and the rest is Mg.