CN108950337B

CN108950337B - Low-cost high-strength Mg-Zn-Y-Ce-Ca magnesium alloy and preparation method thereof

Info

Publication number: CN108950337B
Application number: CN201810890921.8A
Authority: CN
Inventors: 陈先华; 刘晓芳; 潘复生
Original assignee: Chongqing University
Current assignee: Chongqing University
Priority date: 2018-08-07
Filing date: 2018-08-07
Publication date: 2020-06-23
Anticipated expiration: 2038-08-07
Also published as: CN108950337A

Abstract

The invention provides a low-cost high-strength Mg-Zn-Y-Ce-Ca magnesium alloy and a preparation method thereof, wherein the alloy comprises the following components in percentage by mass: 5.0-6.0 wt.% Zn, 0.15-0.45 wt.% Y, 0.15-0.35 wt.% Ce, 0-1.0 wt.% Ca, and the balance of Mg and inevitable impurities. The preparation method comprises the following steps: 1) smelting: placing the material in CO₂And SF₆Heating and melting under the protection of mixed gas, stirring and standing, fishing floating slag, taking out a crucible, putting the crucible into brine, and cooling by water to obtain an ingot; 2) machining to obtain a material with a proper size; 3) preserving heat for 10-12 h at 350 ℃, then preserving heat for 6h at 400 ℃, taking out and quenching to obtain a homogenized material; 4) and extruding the leather at the temperature of 300-350 ℃ according to the extrusion ratio of 25:1 to obtain the magnesium alloy bar. The method has the advantages of rare earth content of about 0.5%, less Ca addition and lower cost. The material has simple preparation process, can improve the mechanical property of the alloy after extrusion deformation, still keeps good plasticity, can replace part of zirconium-containing magnesium alloy materials, and is suitable for 3C products, rail transit parts and the like.

Description

Low-cost high-strength Mg-Zn-Y-Ce-Ca magnesium alloy and preparation method thereof

Technical Field

The invention belongs to the field of metal materials, and particularly relates to a low-cost high-strength Mg-Zn-Y-Ce-Ca magnesium alloy and a preparation method thereof.

Background

Magnesium is the lightest metallic structural material, has a density of only 1.736 g/cm3, is 2/3 for aluminum, and is 1/4 for steel. Meanwhile, the magnesium and the magnesium alloy also have the advantages of high specific strength and specific stiffness, good damping property, cutting processability and thermal conductivity, strong electromagnetic shielding capability, good casting performance, easy recovery and regeneration and the like. In recent years, magnesium and magnesium alloys have been widely used in the automotive, aerospace, electronic and space industries, are known as "green engineering materials for the century", and have become the third largest metallic structural materials following steel and aluminum. However, the crystal structure of magnesium is a close-packed hexagonal structure, and the magnesium has less sliding system at room temperature, low strength and poor plasticity, so that the wide application of the magnesium is limited.

At present, alloying and processing technology change are usually adopted to improve the mechanical property of the alloy. The Mg-Zn series is one of the commercial magnesium alloys widely used at present, the content of Zn in the Mg-Zn binary alloy commonly used by enterprises at home and abroad is about within 4-6% (wt.%), but the simple Mg-Zn binary alloy has the disadvantages of large crystallization temperature range, poor fluidity of metal liquid, difficult casting, difficult corrosion resistance and easy generation of micro-porosity of Zn, thereby causing the tendency of magnesium alloy thermal stress. Therefore, in the actual production, other alloy elements are added into the Mg-Zn alloy, the alloy structure is improved, and the alloy performance is improved, such as Mg-Zn-Zr, Mg-Zn-RE, Mg-Zn-Ca series magnesium alloy and the like.

The performance of the alloy added with high-content rare earth is the most excellent, but the alloy cost can be greatly improved. The Zr-containing Mg-Zn alloy has good room temperature mechanical property, but Zr has high density and serious sedimentation in the smelting process, so more raw materials need to be added for supplement, and resource waste and cost increase are caused. While the formation of large second phases in Mg-Zn-Ca alloys reduces the plasticity of the alloy. Therefore, the development of low-cost magnesium alloy is required continuously, and the mechanical property can be improved by combining the conventional plastic deformation process.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a low-cost high-strength Mg-Zn-Y-Ce-Ca magnesium alloy and a preparation method thereof.

In order to achieve the purpose, the invention adopts the following technical scheme: a low-cost high-strength Mg-Zn-Y-Ce-Ca magnesium alloy comprises the following components in percentage by mass: 5.0-6.0 wt.% Zn, 0.15-0.45 wt.% Y, 0.15-0.35 wt.% Ce, 0-1.0 wt.% Ca, and the balance of Mg and inevitable impurities.

The invention also provides a preparation method of the magnesium alloy, which comprises the following steps: the method comprises the following steps:

1) smelting: preparing raw materials according to the components, wherein the raw materials are pure magnesium ingots, pure zinc ingots, Mg-Y intermediate alloys, Mg-Ce intermediate alloys and Mg-Ca intermediate alloys, preheating the raw materials and a crucible at 200 ℃, preserving heat for 1h, then putting the magnesium ingots into the crucible under the protection of mixed gas of CO2 and SF6, heating the magnesium ingots to 700 ℃ for melting, raising the temperature to 720 ℃ after all the magnesium ingots are melted, putting the zinc ingots and the intermediate alloys into a magnesium solution, stirring for 2-5 minutes after melting to ensure that the components are uniform, standing for 10-20 minutes at 720 ℃, fishing dross on the surface of the melt after the standing is finished, taking out the crucible when the temperature is reduced to 710 ℃, putting the crucible into brine for water cooling, and preparing the required magnesium alloy ingots;

2) machining: turning and sawing the ingot casting to a proper size according to the size of an extrusion cylinder of an extruder;

3) homogenizing: covering the magnesium alloy ingot prepared in the step 2) with graphite, preserving heat for 10-12 h at 350 ℃, then preserving heat for 6h at 400 ℃, taking out and quenching to obtain a homogenized material;

4) hot extrusion: removing the surface oxide skin of the material in the step 3), preheating the material and an extrusion die at 350 ℃ for 1h, and extruding at 300-350 ℃ at an extrusion ratio of 25:1 and an extrusion speed of 0.6-1.2 m/min to obtain the magnesium alloy bar.

The invention has the beneficial effects that:

1. the alloy provided by the invention is added with trace rare earth elements Y, Ce and Ca, and can be combined with Mg and Zn to form high-melting-point Mg-Zn-Y, Mg-Zn-Ce and Mg-Zn-Ca ternary phases. The homogenization heat treatment before extrusion can re-dissolve the second phase part into the matrix, thereby effectively reducing the macro segregation of the alloy. The second phase still remained in the matrix in the extrusion process can be broken into fine particles which are distributed along the extrusion direction, dynamic recrystallization can be effectively promoted, the dispersed phase dynamically precipitated in the extrusion process is distributed in the matrix, and the fine second phase particles and the precipitated phase can pin grain boundaries to hinder the growth of recrystallized grains, so that fine recrystallized grains and a large-sized unrecrystallized area with a large amount of precipitated phases are obtained. The fine crystal grains and a large amount of precipitated phases are very beneficial to strengthening the matrix, after extrusion, the yield strength can reach 320MPa, the tensile strength can reach 361MPa, the tensile strength is obviously higher than that of the commercial ZK60 magnesium alloy, and meanwhile, the better elongation rate is kept.

2. The alloy raw materials of the invention are zinc ingot and Mg-Ca intermediate alloy with relatively low price and rare earth intermediate alloy Mg-Y, Mg-Ce with relatively low price, and trace addition alloy elements are added in the prepared alloy, thus fully utilizing the comprehensive effect of the material.

3. The invention has simple process and easy operation, and the adopted smelting furnace, heat treatment furnace and heat extruder are all conventional equipment, thus being easy to realize in industry and having lower production cost.

4. The content of rare earth added into the magnesium alloy is controlled to be about 0.5 percent, the addition of Ca is less, and the cost is lower. The material has simple preparation process, can improve the mechanical property of the alloy after extrusion deformation, still keeps good plasticity, can replace part of zirconium-containing magnesium alloy materials, and is suitable for 3C products, rail transit parts and the like.

Drawings

FIG. 1 is a metallographic photograph of an extruded microstructure of a magnesium alloy in example 1

FIG. 2 is a metallographic photograph of an extruded microstructure of a magnesium alloy in example 2

FIG. 3 is a metallographic photograph of an extruded microstructure of a magnesium alloy in example 3

FIG. 4 is a metallographic photograph of an extruded microstructure of the magnesium alloy of example 4.

Detailed Description

The present invention will be further described with reference to the following embodiments, which are provided for illustration and not for limitation, and the scope of the present invention is not limited to the following embodiments.

The purity of the industrial pure magnesium and pure zinc ingots in the following examples is more than 99.95%, Y is added in the form of 25% magnesium-yttrium intermediate alloy, Ce is added in the form of 20% magnesium-cerium intermediate alloy, Ca is added in the form of 20% magnesium-calcium intermediate alloy, and the smelting protective gas is CO₂And SF₆Mixed gas (ratio 99: 1).

Example 1:

a novel low-cost high-strength Mg-Zn-Y-Ce-Ca magnesium alloy comprises the following components in percentage by mass: zn5.38 wt.%, Y0.34 wt.%, Ce 0.19 wt.%, the balance Mg.

The magnesium alloy of the embodiment can be obtained by the following preparation according to the proportion:

1) alloy smelting and casting: the raw materials used are pure magnesium ingot, pure zinc ingot, Mg-25 wt.% of Y master alloy and Mg-20wt.% of Ce master alloy. Preheating raw materials and a crucible at 200 ℃, preserving heat for 1h, and then adding CO₂And SF₆Under the protection of mixed gas (the proportion is 99: 1), putting a magnesium ingot into a crucible, heating the crucible to 700 ℃ for melting, raising the temperature to 720 ℃ after the magnesium ingot is completely melted, putting a zinc ingot and an intermediate alloy into a magnesium melt, stirring for 2-5 minutes after the magnesium ingot is melted to ensure that the components are uniform, standing for 10-20 minutes at 720 ℃, fishing dross on the surface of the melt after the standing is finished, taking out the crucible when the temperature is reduced to 700-;

4) hot extrusion: removing surface oxide skin from the material in the step 3), preheating the material and an extrusion die at 350 ℃ for 1h, and extruding at 350 ℃ at an extrusion ratio of 25:1 and an extrusion speed of 0.6-1.2 m/min to obtain a magnesium alloy rod with the diameter of 16 mm.

Example 2:

a novel low-cost high-strength Mg-Zn-Y-Ce-Ca magnesium alloy comprises the following components in percentage by mass: zn5.10 wt.%, Y0.31 wt.%, Ce 0.18 wt.%, Ca 0.29 wt.%, and the balance Mg.

1) alloy smelting and casting: the raw materials used are pure magnesium ingot, pure zinc ingot, Mg-25 wt.% of Y master alloy, Mg-20wt.% of Ce master alloy and Mg-20wt.% of Ca master alloy. Preheating raw materials and a crucible at 200 ℃, preserving heat for 1h, and then adding CO₂And SF₆Under the protection of mixed gas (ratio is 99: 1), putting magnesium ingot into crucible, heating to 700 deg.C for melting, heating to 720 deg.C, putting zinc ingot and intermediate alloy into molten magnesium, and meltingStirring for 2-5 minutes after melting to ensure that the components are uniform, standing for 10-20 minutes at 720 ℃, fishing dross on the surface of the melt after the standing is finished, taking out the crucible when the temperature is reduced to 700-;

2) machining: same as example 1

3) Homogenizing: same as example 1

4) Hot extrusion: same as example 1

Example 3:

a novel low-cost high-strength Mg-Zn-Y-Ce-Ca magnesium alloy comprises the following components in percentage by mass: zn5.1wt.%, Y0.37 wt.%, Ce 0.17 wt.%, Ca 0.61 wt.%, and the balance Mg. The alloy smelting-machining-homogenizing-hot extrusion method for obtaining the magnesium alloy of the present example was the same as in example 2.

Example 4:

a novel low-cost medium-high strength Mg-Zn-Y-Ce-Ca magnesium alloy comprises the following components in percentage by mass: zn5.1wt.%, Y0.36 wt.%, Ce 0.19 wt.%, Ca 0.28 wt.%, and the balance Mg.

1) alloy smelting and casting: the same as example 2;

2) machining: the same as example 2;

3) homogenizing: the same as example 2;

4) hot extrusion: removing surface oxide skin from the material obtained in the step 3), preheating the material and an extrusion die at 350 ℃ for 1h, and extruding at 300 ℃ at an extrusion ratio of 25:1 and an extrusion speed of 0.6-1.2 m/min to obtain a magnesium alloy rod with the diameter of 16 mm.

And (3) mechanical property detection:

tensile test samples of magnesium alloy rods of the above examples 1, 2, 3 and 4 are taken according to GB/T228.1: 2010 nonstandard, and room temperature tensile test is carried out on a CMT-5105 universal tester, and the test results are shown in Table 1.

TABLE 1 Room temperature mechanical properties of the low cost, high strength magnesium alloys of the present invention

It can be seen from table 1 that, by adding a proper amount of Ca to the alloy, the mechanical properties of the alloy are greatly improved after extrusion treatment, and a proper elongation can be maintained, the yield strength in example 3 can reach 321MPa, which is significantly higher than that of ZK60 magnesium alloy, the tensile strength can reach 361MPa, and the elongation is 10.4%. The material can be used as a light structural material for 3C products and rail transit parts.

The organization in fig. 2 and 3 is clearly detailed in comparison with fig. 1. Due to the adoption of a bipolar heat treatment mode, most of the second phase in an as-cast state can be dissolved into the matrix, the second phase remained in the matrix can be crushed into fine particles in extrusion with the extrusion ratio of 25:1 and distributed along the extrusion direction, the second phases can promote dynamic recrystallization formation, elements dissolved into the matrix can be dynamically separated out in the extrusion process, and in the dispersed matrix, fine second phase particles and dispersed phases can pin grain boundaries and prevent recrystallized grains from growing. FIG. 3 shows that there are many broken second phases in the alloy, and the energy spectrum analysis shows that the alloy is Mg-Zn-Y I phase, Mg-Zn-Ce phase and Ca2Mg6Zn3 phase. These second phases can pin dislocation motion and improve the mechanical properties of the alloy.

Finally, the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and the technical solutions of the present invention should be covered by the claims of the present invention.

Claims

1. A novel low-cost high-strength Mg-Zn-Y-Ce-Ca magnesium alloy is characterized by comprising the following components in percentage by mass: zn5.1wt.%, Y0.37 wt.%, Ce 0.17 wt.%, Ca 0.61 wt.%, the balance Mg;

the preparation method of the magnesium alloy comprises the following steps:

1) alloy smelting and casting: the raw materials are pure magnesium ingot, pure zinc ingot, Mg-25 wt.% of Y master alloy and Mg-20wt.% of Ce master alloyMg-20wt.% Ca master alloy; preheating raw materials and a crucible at 200 ℃, preserving heat for 1h, and then adding CO₂：SF₆Under the protection of mixed gas of 99:1, putting a magnesium ingot into a crucible, heating the magnesium ingot to 700 ℃ for melting, raising the temperature to 720 ℃ after the magnesium ingot is completely melted, putting a zinc ingot and an intermediate alloy into a magnesium solution, stirring the magnesium solution for 2 to 5 minutes after the magnesium ingot is melted to ensure that the components are uniform, standing the magnesium ingot at 720 ℃ for 10 to 20 minutes, fishing floating slag on the surface of the melt after the magnesium ingot is completely stood, taking out the crucible when the temperature is reduced to 700-;