CN108950337B - A kind of low-cost high-strength Mg-Zn-Y-Ce-Ca magnesium alloy and preparation method thereof - Google Patents

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

A kind of 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, in particular to a low-cost and high-strength Mg-Zn-Y-Ce-Ca magnesium alloy and a preparation method thereof.

Background technique

Magnesium is the lightest metal structural material, with a density of only 1.736 g/cm3, 2/3 of aluminum and 1/4 of steel. At the same time, magnesium and its alloys also have the advantages of high specific strength, specific stiffness, good damping, machinability and thermal conductivity, as well as strong electromagnetic shielding ability, good casting performance and easy recycling. In recent years, magnesium and magnesium alloys have been widely used in the automotive, aerospace, electronics and space industries, known as "the green engineering materials of the century", and have become the third largest metal structural materials after steel and aluminum. However, the crystal structure of magnesium is a close-packed hexagonal structure, with few slip systems at room temperature, low strength and poor plasticity, which limit its wide application.

At present, alloying and changing the processing technology are usually used to improve the mechanical properties of the alloy. Mg-Zn system is one of the widely used commercial magnesium alloys. The content of Zn in Mg-Zn binary alloys commonly used by domestic and foreign companies is about 4%-6% (wt.%), but pure Mg- Due to the large crystallization temperature range of Zn binary alloys, the fluidity of molten metal is poor, it is not easy to cast, and it is not resistant to corrosion, and Zn is prone to microscopic porosity, which causes the tendency of magnesium alloys to be hot. Therefore, in actual production, Mg-Zn alloys should be added with other alloying elements to improve the alloy structure and improve the alloy properties, such as Mg-Zn-Zr, Mg-Zn-RE, Mg-Zn-Ca and other magnesium alloys.

Among them, adding high-content rare earth alloys has the best performance, but the cost of alloys will increase significantly. The room temperature mechanical properties of Zr-containing Mg-Zn alloys are good, but during the smelting process, Zr has serious sedimentation due to its high density, and more raw materials need to be added to supplement it, resulting in waste of resources and increased cost. The formation of bulk second phase in Mg-Zn-Ca alloys will reduce the ductility of the alloys. Therefore, there is an urgent need to continue to develop low-cost magnesium alloys that can be combined with conventional plastic deformation processes to improve mechanical properties.

SUMMARY OF THE INVENTION

In view of the above deficiencies in the prior art, the purpose of the present invention is to provide a low-cost and high-strength Mg-Zn-Y-Ce-Ca magnesium alloy, and the present invention also provides a preparation method of the magnesium alloy.

In order to achieve the above purpose, the present invention adopts the following technical scheme: a low-cost and high-strength Mg-Zn-Y-Ce-Ca magnesium alloy, the composition mass percentages are: Zn 5.0~6.0 wt.%, Y 0.15~0.45 wt.% , Ce 0.15~0.35 wt.%, Ca 0~1.0 wt.%, and the rest are Mg and inevitable impurities.

The present invention also provides a preparation method of the magnesium alloy, comprising the following steps:

1) Smelting: prepare raw materials according to the stated components. The raw materials used are pure magnesium ingots, pure zinc ingots, Mg-Y master alloys, Mg-Ce master alloys, and Mg-Ca master alloys. Preheating, holding for 1h, then under the protection of CO2 and SF6 mixed gas, put the magnesium ingot into the crucible and heat it to 700 ℃ to melt, after all melting, raise the temperature to 720 ℃, put the zinc ingot and the master alloy into the magnesium melt , stir for 2~5 minutes after melting to make the composition uniform, let stand at 720℃ for 10~20 minutes, after standing, salvage the scum on the surface of the melt, when the temperature drops to 700-710℃, take out the crucible and put it in brine Medium water cooling to prepare the required magnesium alloy ingots;

2) Machining: according to the size of the extrusion barrel of the extruder, cut the above ingot car skin and saw to the appropriate size;

3) Homogenization: the magnesium alloy ingot prepared in step 2) is covered with graphite, kept at 350°C for 10-12 hours, then kept at 400°C for 6 hours, taken out and quenched to obtain a homogenized material;

4) Hot extrusion: remove the surface oxide scale from the material in step 3), and preheat the extrusion die at 350°C for 1 hour, extrude at 300°C~350°C, the extrusion ratio is 25:1, and the extrusion The speed is 0.6~1.2 m/min to obtain magnesium alloy rods.

The beneficial effects of the present invention are:

1. The alloy proposed by the invention adds trace rare earth elements Y, Ce and Ca, and combines with Mg and Zn to form ternary phases of Mg-Zn-Y, Mg-Zn-Ce and Mg-Zn-Ca with high melting point. The homogenization heat treatment before extrusion can re-dissolve the second phase into the matrix, effectively reducing the macrosegregation of the alloy. During the extrusion process, the second phase still remaining in the matrix will be broken into fine particles and distributed along the extrusion direction, which can effectively promote dynamic recrystallization. Two-phase particles and precipitates can pin the grain boundaries, hinder the growth of recrystallized grains, and obtain fine recrystallized grains and coarse unrecrystallized regions with a large number of precipitates. The fine grains and a large number of precipitates are very beneficial to the strengthening of the matrix. After extrusion, the yield strength can reach 320MPa, and the tensile strength can reach 361MPa, which is significantly higher than the commercial ZK60 magnesium alloy, while maintaining a good elongation.

2. The alloy raw materials of the invention are relatively low-priced zinc ingots and Mg-Ca master alloys, and relatively cheap rare earth master alloys Mg-Y and Mg-Ce, and the alloys are prepared by adding a small amount of alloying elements, making full use of the Synthesis of materials.

3. The process of the invention is simple and easy to operate, and the adopted smelting furnace, heat treatment furnace and hot extrusion machine are all conventional equipment, which is easy to realize in industry and has low production cost.

4. The content of rare earth added to the magnesium alloy of the present invention is controlled at about 0.5%, the amount of Ca added is also relatively small, and the cost is low. The material preparation process is simple, the mechanical properties of the alloy can be improved after extrusion deformation, and the plasticity is still maintained. It can replace some zirconium-containing magnesium alloy materials, and is suitable for 3C products, rail transit parts, etc.

Description of drawings

Fig. 1 is the metallographic photograph of the extruded microstructure of magnesium alloy in Example 1

Fig. 2 is the metallographic photograph of the extruded microstructure of the magnesium alloy in Example 2

Figure 3 is a metallographic photograph of the extruded microstructure of the magnesium alloy in Example 3

FIG. 4 is a metallographic photograph of the extruded microstructure of the magnesium alloy in Example 4. FIG.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be noted that these embodiments are used to illustrate the present invention rather than limit the present invention, and the protection scope of the present invention is not limited to the following embodiments.

In the following examples, the purity of industrial pure magnesium and pure zinc ingots is above 99.95%, Y is added in the form of 25% magnesium-yttrium master alloy, Ce is added in the form of 20% magnesium-cerium master alloy, and Ca is It is added in the form of 20% magnesium-calcium master alloy, and the smelting protective gas is a mixture of CO ₂ and SF ₆ (the ratio is 99:1).

Example 1:

A novel low-cost and high-strength Mg-Zn-Y-Ce-Ca magnesium alloy comprises the following components by mass percentage: Zn 5.38 wt.%, Y 0.34 wt.%, Ce 0.19 wt.%, and the balance is Mg.

Prepare by above-mentioned proportioning and following manner, just can obtain the magnesium alloy of this embodiment:

1) Alloy smelting and casting: The raw materials used are pure magnesium ingot, pure zinc ingot, Mg-25 wt.%Y master alloy, and Mg-20 wt.% Ce master alloy. First, the raw materials and the crucible were preheated at 200°C and kept for 1 h. Then, under the protection of the mixed gas of CO ₂ and SF ₆ (99:1 ratio), the magnesium ingot was put into the crucible and heated to 700°C for melting. Raise the temperature to 720°C, put the zinc ingot and master alloy into the magnesium melt, stir for 2~5 minutes after melting to make the composition uniform, let stand at 720°C for 10~20 minutes, and salvage the melt after standing Surface scum, when the temperature drops to 700-710°C, take out the crucible and put it in brine for water cooling to prepare the required magnesium alloy ingot;

2) Machining: According to the size of the extrusion barrel of the extruder, the above ingot car skin and sawing are cut to the appropriate size;

3) Homogenization: the magnesium alloy ingot prepared in step 2) is covered with graphite, kept at 350°C for 10-12 hours, then kept at 400°C for 6 hours, taken out and quenched to obtain the homogenized material;

4) Hot extrusion: remove the surface oxide scale from the material in step 3), and preheat the extrusion die at 350 °C for 1 h, and extrude at 350 °C, the extrusion ratio is 25:1, and the extrusion speed is 0.6 ~1.2 m/min to obtain magnesium alloy rods with a diameter of 16 mm.

Example 2:

A novel low-cost high-strength Mg-Zn-Y-Ce-Ca magnesium alloy, comprising the following components by mass percentage: Zn5.10 wt.%, Y 0.31 wt.%, Ce 0.18 wt.%, Ca 0.29 wt.% , the remainder is Mg.

Prepare by above-mentioned proportioning and following manner, just can obtain the magnesium alloy of this embodiment:

1) Alloy smelting and casting: The raw materials used are pure magnesium ingot, pure zinc ingot, Mg-25 wt.%Y master alloy, Mg-20 wt.% Ce master alloy, and Mg-20 wt.% Ca master alloy. First, the raw materials and the crucible were preheated at 200°C and kept for 1 h. Then, under the protection of the mixed gas of CO ₂ and SF ₆ (99:1 ratio), the magnesium ingot was put into the crucible and heated to 700°C for melting. Raise the temperature to 720°C, put the zinc ingot and master alloy into the magnesium melt, stir for 2~5 minutes after melting to make the composition uniform, let stand at 720°C for 10~20 minutes, and salvage the melt after standing Surface scum, when the temperature drops to 700-710°C, take out the crucible and put it in brine for water cooling to prepare the required magnesium alloy ingot;

2) Machining: same as Example 1

3) Homogenization: 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, comprising the following components by mass percentage: Zn 5.1 wt.%, Y 0.37 wt.%, Ce 0.17 wt.%, Ca 0.61 wt.%, The balance is Mg. The alloy smelting-machining-homogenization-hot extrusion method for obtaining the magnesium alloy of this example is the same as that of Example 2.

Example 4:

A novel low-cost medium and high-strength Mg-Zn-Y-Ce-Ca magnesium alloy, comprising the following components by mass percentage: Zn5.1 wt.%, Y 0.36 wt.%, Ce 0.19 wt.%, Ca 0.28 wt.% , the remainder is Mg.

Prepare by above-mentioned proportioning and following manner, just can obtain the magnesium alloy of this embodiment:

1) alloy smelting and casting: same as Example 2;

2) Machining: same as Example 2;

3) Homogenization: the same as in Example 2;

4) Hot extrusion: the surface oxide scale is removed from the material in step 3), and the extrusion die is preheated at 350 ° C for 1 h, and extruded at 300 ° C, the extrusion ratio is 25:1, and the extrusion speed is 0.6 ~1.2 m/min to obtain magnesium alloy rods with a diameter of 16 mm.

Mechanical property testing:

Using GB/T 228.1:2010 non-standard, take the above-mentioned examples 1, 2, 3 and 4 magnesium alloy bars to process tensile samples, and carry out room temperature tensile test on CMT-5105 universal testing machine. The test results are shown in Table 1.

Table 1 Room temperature mechanical properties of the low-cost, medium- and high-strength magnesium alloy according to the present invention

It can be seen from Table 1 that adding an appropriate amount of Ca to the alloy, after extrusion treatment, the mechanical properties of the alloy are greatly improved, and the appropriate 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%. It can be used as 3C products and lightweight structural materials for rail transit parts.

Comparing Fig. 1, the tissues in Fig. 2 and Fig. 3 are obviously refined. Due to the bipolar heat treatment method, most of the second phase in the as-cast state can be dissolved into the matrix, while the second phase remaining in the matrix will be broken into fine particles during extrusion with an extrusion ratio of 25:1 and Distributed along the extrusion direction, these second phases can promote the formation of dynamic recrystallization. The elements dissolved into the matrix will be dynamically precipitated during the extrusion process. In the dispersed matrix, the fine second phase particles and dispersed phases can pin the crystals. boundary, hindering the growth of recrystallized grains. Figure 3 shows that there are many broken second phases in the alloy, which are Mg-Zn-Y I phase, Mg-Zn-Ce phase, and Ca2Mg6Zn3 phase by energy spectrum analysis. These second phases can pin the dislocation movement and improve the mechanical properties of the alloy.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be Modifications or equivalent replacements without departing from the spirit and scope of the technical solutions of the present invention shall be covered by the scope of the claims of the present invention.

Claims (1)

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-;

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 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.

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