阅读说明：本技术 一种高含锶（Sr）量的镁合金及其制备方法 (Magnesium alloy with high strontium (Sr) content and preparation method thereof ) 是由 张娜 于 2020-06-01 设计创作，主要内容包括：本发明涉及一种高含锶(Sr)量的镁合金及其制备方法,属于镁合金技术领域。该镁合金按质量百分比计,由以下组分组成：Sr：1～3％,Mn：0.15～0.4％,Al：5.9～6.2％,Zn：0.8～1.2％,杂质元素总量：<0.1％,余量为Mg。将合金熔体浇铸至铁制模具中,得到铸锭；将铸锭热处理后车削,去除表面氧化部分,加工为Φ70mm的合金棒材,挤压经过液氮冷却后得到Φ16mm的镁合金挤压棒,并在挤压棒上涂一层蛋白质。本发明所制得的镁合金在350℃挤压后的室温力学性能为：抗拉强度可达到260～307MPa,屈服强度可达到207～255MPa,延伸率可达到5～9.5％。该制备方法操作简单,成本低,有利于工业化生产。(The invention relates to a magnesium alloy with high strontium (Sr) content and a preparation method thereof, belonging to the technical field of magnesium alloys. The magnesium alloy comprises the following components in percentage by mass: sr: 1-3%, Mn: 0.15-0.4%, Al: 5.9-6.2%, Zn: 0.8-1.2%, total amount of impurity elements: < 0.1%, the balance being Mg. Casting the alloy melt into an iron mould to obtain a cast ingot; turning after heat treatment of the cast ingot, removing surface oxidation parts, processing into an alloy bar with the diameter phi of 70mm, extruding and cooling by liquid nitrogen to obtain a magnesium alloy extrusion bar with the diameter phi of 16mm, and coating a layer of protein on the extrusion bar. The room temperature mechanical properties of the magnesium alloy prepared by the invention after extrusion at 350 ℃ are as follows: the tensile strength can reach 260-307 MPa, the yield strength can reach 207-255 MPa, and the elongation can reach 5-9.5%. The preparation method is simple to operate, low in cost and beneficial to industrial production.)

1. The magnesium alloy with high strontium (Sr) content is characterized by comprising the following components in percentage by mass: sr: 1-3%, Mn: 0.15-0.4%, Al: 5.9-6.2%, Zn: 0.8-1.2%, total amount of impurity elements: < 0.1%, the balance being Mg.

2. The magnesium alloy with high strontium (Sr) content according to claim 1, wherein the magnesium alloy comprises the following components in percentage by mass: 1% of Sr, 0.4% of Mn, 6.2% of Al, 1.2% of Zn and the balance of Mg.

3. The magnesium alloy with high strontium (Sr) content according to claim 1, wherein the magnesium alloy comprises the following components in percentage by mass: 2% of Sr, 0.15% of Mn, 5.9% of Al, 0.8% of Zn and the balance of Mg.

4. The magnesium alloy with high strontium (Sr) content according to claim 1, wherein the magnesium alloy comprises the following components in percentage by mass: 3% of Sr, 0.2% of Mn, 6% of Al, 1% of Zn and the balance of Mg.

5. A preparation method of magnesium alloy with high strontium (Sr) content is characterized by comprising the following steps:

(1) adopting a well-type resistance smelting furnace, adding preheated pure Mg and melting the Mg when the temperature of the smelting furnace reaches 500-600 ℃, heating the Mg to 700-750 ℃ after melting, adding preheated Mg-25 wt.% Sr, Mg-5 wt.% Mn, pure Al and pure Zn, heating the Mg-25 wt.% Sr, Mg-5 wt.% Mn, pure Al and pure Zn to 720-740 ℃ after the metals and the alloys are melted, and then using C₂Cl₆Refining for 3-5 min by using a refining agent, stirring and slagging after refining, heating to 740 ℃, and standing for 20-40 min; the casting process utilizes CO in volume ratio₂:SF₆The mixed gas protection of 20:1 is carried out to prevent the alloy liquid from oxidizing and burning; casting the metal melt into a steel mould preheated to 250 ℃ to obtain a cast ingot;

(2) turning a magnesium alloy ingot, removing a surface oxidation part, processing the magnesium alloy ingot into an alloy bar with the diameter of 70mm, then preserving heat for 16-24 hours at 400-450 ℃, and carrying out homogenization heat treatment;

(3) extruding the alloy on an extruder at an extrusion speed of 50cm/min to obtain a magnesium alloy extruded bar with the diameter of 16mm, wherein the extrusion temperature is 350 ℃, and the extrusion ratio is 25: 1;

(4) and cooling the extruded magnesium alloy section by liquid nitrogen, and coating a layer of protein on the surface of the section.

6. The method for preparing the magnesium alloy with high strontium (Sr) content according to claim 5, wherein in the step (3), high-purity oxygen is introduced during the extrusion process to oxidize the surface of the magnesium alloy.

7. The method for preparing the magnesium alloy with high strontium (Sr) content according to claim 5, wherein the high purity oxygen is introduced in the step (3) by a high pressure pulse oxygen introduction method.

Technical Field

The invention belongs to the technical field of magnesium alloy, and particularly relates to a magnesium alloy with high strontium (Sr) content and a preparation method thereof.

Background

Strontium (Sr) is an important alkaline earth metal element, has relatively low price, has small solid solubility in magnesium alloy, but has a fine-grain strengthening effect on the magnesium alloy, and a high-melting-point compound introduced by Sr can play a good strengthening effect on the grain boundary of the magnesium alloy, thereby effectively improving the mechanical property of the magnesium alloy. In addition, the proper amount of Sr is added into the magnesium alloy, so that the casting performance of the alloy can be improved and the generation of casting defects can be reduced besides refining and modifying the structure of the alloy.

At present, because the magnesium alloy is preheated before extrusion and the friction heat is generated in the extrusion process, the temperature of an extruded section is very high after extrusion, so that the dynamic recrystallization of the magnesium alloy grows, and the mechanical property of the extruded section is seriously influenced. And the surface of the extruded Mg-Sr alloy is easy to corrode after being placed for a period of time, and protein can form an adsorption layer on the surface of magnesium and the magnesium alloy, so that the corrosion rate of the magnesium is reduced.

Disclosure of Invention

In view of the above, an object of the present invention is to provide a magnesium alloy with a high strontium (Sr) content; the second purpose is to improve the mechanical property and the surface corrosion resistance of the magnesium alloy containing high strontium (Sr).

In order to achieve the purpose, the invention provides the following technical scheme:

1. a preparation method of a high strontium (Sr) magnesium alloy comprises the following steps:

(1) adopting a well-type resistance smelting furnace, adding preheated pure Mg and melting the Mg when the temperature of the smelting furnace reaches 500-600 ℃, heating the Mg to 700-750 ℃ after melting, adding preheated Mg-25 wt.% Sr, Mg-5 wt.% Mn, pure Al and pure Zn, heating the Mg-25 wt.% Sr, Mg-5 wt.% Mn, pure Al and pure Zn to 720-740 ℃ after the metals and the alloys are melted, and then using C₂Cl₆Refining for 3-5 min by using a refining agent, stirring and slagging after refining, heating to 740 ℃, and standing for 20-40 min; the casting process utilizes CO in volume ratio₂:SF₆The mixed gas protection of 20:1 is carried out to prevent the alloy liquid from oxidizing and burning; casting the metal melt into a steel mould preheated to 250 ℃ to obtain a cast ingot;

(2) turning a magnesium alloy ingot, removing a surface oxidation part, processing the magnesium alloy ingot into an alloy bar with the diameter of 70mm, then preserving heat for 16-24 hours at 400-450 ℃, and carrying out homogenization heat treatment;

(3) extruding the alloy on an extruder at an extrusion speed of 50cm/min to obtain a magnesium alloy extruded bar with the diameter of 16mm, wherein the extrusion temperature is 350 ℃ and the extrusion ratio is 25: 1.

(4) And cooling the extruded magnesium alloy section by liquid nitrogen, and coating a layer of protein on the surface of the section.

In the step (1), the magnesium alloy ingot with high strontium content (Sr) comprises the following components in percentage by mass: sr: 1-3%, Mn: 0.15-0.4%, Al: 5.9-6.2%, Zn: 0.8-1.2%, total amount of impurity elements: < 0.1%, the balance being Mg.

Further: and cooling the extruded magnesium alloy section by liquid nitrogen, and coating a layer of protein on the surface of the section.

Further: in the step (3), high-purity oxygen is introduced in the extrusion process to oxidize the surface of the magnesium alloy, and the pure oxygen can obtain an extremely thin high-purity magnesium oxide layer, so that the friction force between the alloy body and equipment can be reduced, and the magnesium alloy can be prevented from being further oxidized.

Further: in the step (3), the method for introducing oxygen is to adopt a high-pressure oxygen pulse type introduction mode, so that the high-pressure oxygen is contacted with the magnesium alloy in an ultrasonic impact mode, the structure of the magnesium alloy can be improved, the tensile stress of the bar in the extrusion process is reduced, and holes and cracks in the magnesium alloy extruded bar can be effectively reduced.

2. The magnesium alloy with high strontium (Sr) content prepared by the preparation method

The invention has the beneficial effects that: compared with the prior art, the invention provides the high-strontium (Sr) magnesium alloy and the preparation method thereof, and the Mg-Al-Zn-Mn-Sr magnesium alloy with high comprehensive performance is obtained by scientific alloying component design and proper heat treatment process and extrusion process. Under the condition of room temperature, the tensile strength of the wrought magnesium alloy can reach 260-307 MPa, the yield strength can reach 207-255 MPa, and the elongation can reach 5-9.5%. Wherein Al is the most common alloy element in magnesium alloy, Al mainly shows solid solution strengthening and time effect strengthening in Mg, the solubility of Al in Mg decreases with temperature reduction, when the alloy is solidified or agedIn time, the supersaturated solid solution precipitates dispersed and balanced beta-Mg₁₇Al₁₂Strengthening phase to improve the strength of magnesium alloy; the maximum solubility of Zn in magnesium is 6.2 wt%, and the solid solubility of Zn decreases significantly with the decrease of temperature, and decreases to 2% or less at 100 ℃. When the zinc content is small (<l%) the role of zinc in magnesium is expressed on the one hand as its own solid solution strengthening; on the other hand, a small amount of zinc can also increase the solubility of aluminum in magnesium and improve the solid solution strengthening effect of aluminum. In addition, the corrosion resistance of the Mg-Al alloy can be greatly improved after a small amount of Zn is added into the Mg-Al alloy. Adding surface active elements enriched on the surface of the crystal grains and the positions of the grain boundaries to fill crystal lattice vacancies at the grain boundaries and improve the tissue morphology near the grain boundaries. The Sr element is added into the magnesium alloy, so that the alloy structure can be obviously refined, the structure uniformity is improved, and the casting defects are reduced; the solid solubility of the element Sr in the magnesium alloy is only 0.11 percent, and the Sr is extruded to the front edge of a solid-liquid interface in the solidification process, so that the Sr content of the solidification interface is higher, and Al with a high melting point is formed in the magnesium alloy₄The Sr phase has thermal stability, can pin the grain boundary and prevent the grain boundary from sliding, and plays a role in strengthening the grain boundary so as to effectively improve the comprehensive mechanical property of the alloy. The main purpose of adding Mn element into magnesium alloy is to improve the stress corrosion resistance tendency of the alloy, thereby improving the corrosion resistance and changing the welding performance of the alloy. Mn can improve the corrosion resistance of the magnesium alloy, mainly because the addition of Mn can improve the potential of the alloy on one hand, and Mn can form Alx (Fe, Mn) y compounds with Fe in the alloy to be eliminated as slag, thereby eliminating the harmful influence of Fe on the corrosion resistance of the magnesium alloy. The preparation method disclosed by the invention is simple and easy to operate, only needs conventional equipment, is low in cost and is suitable for industrial production.

Drawings

In order to make the object, technical scheme and beneficial effect of the invention more clear, the invention provides the following drawings for explanation:

FIG. 1 is a metallographic microstructure photograph of a sheared portion of a magnesium alloy having a high strontium (Sr) content after extrusion in example 1;

FIG. 2 is a metallographic microstructure photograph of a magnesium alloy with a high strontium (Sr) content prepared in example 2;

FIG. 3 is a metallographic microstructure photograph of a magnesium alloy with a high strontium (Sr) content prepared in example 3;

FIG. 4 is a metallographic microstructure photograph of a magnesium alloy with a high strontium (Sr) content prepared in example 4;

FIG. 5 is a graph showing true strain and true stress curves of the high strontium (Sr) content magnesium alloys prepared in examples 2, 3, and 4.

Detailed Description

The preferred embodiments of the present invention will be described in detail below.