CN108950337A - 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. The components of the alloy 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 unavoidable impurities. The preparation method includes: 1) smelting: heat and melt the material under the protection of a mixed gas of CO ₂ and SF ₆ , stir and let it stand, salvage the scum, take out the crucible and put it in salt water to cool in water, and make an ingot; 2) machining to obtain a suitable Size material; 3) heat preservation at 350°C for 10~12h, then heat preservation at 400°C for 6h, take out and quench, and obtain homogenized material; Extrude at ℃ to obtain magnesium alloy rods. The rare earth content added by this method is about 0.5%, the amount of Ca added is relatively small, and the cost is low. The material preparation process is simple, and the mechanical properties of the alloy can be improved after extrusion deformation, and the plasticity can still be maintained. It can replace some magnesium alloy materials containing zirconium, and is suitable for 3C products, rail transit parts, etc.

Description

A low-cost high-strength Mg-Zn-Y-Ce-Ca magnesium alloy and its preparation method

technical field

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

Background technique

Magnesium is the lightest metal structure material with a density of only 1.736 g/cm3, which is 2/3 of aluminum and 1/4 of steel. At the same time, magnesium and its alloys also have high specific strength, specific stiffness, good damping, machinability and thermal conductivity, strong electromagnetic shielding ability, good casting performance and easy recycling and regeneration. In recent years, magnesium and magnesium alloys have been widely used in automobiles, aerospace, electronics and space industries, known as "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, which has few slip systems at room temperature, low strength, and poor plasticity, which limits its wide application.

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

Among them, the alloy with high content of rare earth has the best performance, but the cost of the alloy will be greatly increased. The mechanical properties of Mg-Zn alloys containing Zr are better at room temperature, but the Zr subsides seriously due to its high density during the smelting process, and more raw materials need to be added for supplementation, resulting in waste of resources and increased costs. However, the formation of bulky second phases in Mg-Zn-Ca alloys will reduce the plasticity 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.

Contents of the invention

In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a low-cost 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 object, the present invention adopts the following technical scheme: a low-cost high-strength Mg-Zn-Y-Ce-Ca magnesium alloy, the composition mass percentage is: 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 unavoidable 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. Preheat and keep warm for 1 hour, then under the protection of CO2 and SF6 mixed gas, put the magnesium ingot into the crucible and heat it to 700°C to melt. After melting, stir for 2-5 minutes to make the ingredients uniform, and let it stand at 720°C for 10-20 minutes. After standing, remove the scum on the surface of the melt. When the temperature drops to 700-710°C, take out the crucible and put it in salt water. Medium water cooling to prepare the required magnesium alloy ingot;

2) Machining: According to the size of the extruder cylinder, the above-mentioned cast ingot car skin and sawing are cut to a suitable size;

3) Homogenization: cover the magnesium alloy ingot prepared in step 2) with graphite, keep it at 350°C for 10-12h, then keep it at 400°C for 6h, take it out and quench it, and obtain the homogenized material;

4) Hot extrusion: Remove the surface scale from the material in step 3), preheat the extrusion die at 350°C for 1 hour, and extrude at 300°C~350°C, with an extrusion ratio of 25:1, and extrude 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, Ca, and combines with Mg, Zn to form Mg-Zn-Y, Mg-Zn-Ce, Mg-Zn-Ca ternary phase with high melting point. The homogenization heat treatment before extrusion can partially re-dissolve the second phase into the matrix, effectively reducing the macro-segregation of the alloy. The second phase still remaining in the matrix during the extrusion process will be broken into fine particles and distributed along the extrusion direction, which can effectively promote dynamic recrystallization. The dispersed phase dynamically precipitated during the extrusion process is distributed in the matrix. These fine first phases Two-phase grains and precipitated phases can pin the grain boundaries and hinder the growth of recrystallized grains, resulting in fine recrystallized grains and coarse unrecrystallized regions with a large number of precipitated phases. Fine grains and a large number of precipitated phases are very conducive to matrix strengthening. 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 present invention are relatively low price zinc ingots and Mg-Ca master alloys, and relatively cheap rare earth master alloys Mg-Y and Mg-Ce, and alloy elements are added in a small amount in the prepared alloys, making full use of the Combination of materials.

3. The process of the invention is simple and easy to operate, and the adopted smelting furnace, heat treatment furnace and hot extruding machine are all conventional equipments, which is easy to implement industrially 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 relatively small, and the cost is low. The material preparation process is simple, and the mechanical properties of the alloy can be improved after extrusion deformation, and the plasticity can still be maintained. It can replace some magnesium alloy materials containing zirconium, and is suitable for 3C products, rail transit parts, etc.

Description of drawings

Fig. 1 is the metallographic photo of embodiment 1 magnesium alloy extrusion microstructure

Fig. 2 is the metallographic photo of embodiment 2 magnesium alloy extrusion microstructure

Fig. 3 is the metallographic photograph of the extruded microstructure of the magnesium alloy of Example 3

Fig. 4 is a metallographic photo of the extruded microstructure of the magnesium alloy of Example 4.

Detailed ways

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

The purity of industrial pure magnesium and pure zinc ingots described in the following examples are all 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 melting protective gas is a mixed gas of CO ₂ and SF ₆ (the ratio is 99:1).

Example 1:

A new low-cost high-strength Mg-Zn-Y-Ce-Ca magnesium alloy, including the following components by mass percentage: Zn 5.38wt.%, 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 present 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. First, preheat the raw materials and crucible at 200°C and keep it warm for 1 hour. Then, under the protection of CO ₂ and SF ₆ mixed gas (the ratio is 99:1), put the magnesium ingot into the crucible and heat it to 700°C for melting. Raise the temperature to 720°C, put the zinc ingot and the master alloy into the molten magnesium, stir for 2-5 minutes after melting to make the composition uniform, and let it 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 salt water for water cooling to prepare the required magnesium alloy ingot;

2) Machining: According to the size of the extruder barrel, the above-mentioned cast ingot car body is sawed to a suitable size;

3) Homogenization: Cover the magnesium alloy ingot prepared in step 2) with graphite, keep it warm at 350°C for 10-12h, then keep it at 400°C for 6h, take it out and quench it, and obtain the homogenized material;

4) Hot extrusion: Remove the surface scale from the material in step 3), preheat the extrusion die at 350°C for 1 hour, and extrude at 350°C with an extrusion ratio of 25:1 and an extrusion speed of 0.6 ~1.2 m/min, a magnesium alloy rod with a diameter of 16 mm was obtained.

Example 2:

A new low-cost high-strength Mg-Zn-Y-Ce-Ca magnesium alloy, including the following components by mass percentage: Zn 5.10wt.%, Y 0.31 wt.%, Ce 0.18 wt.%, Ca 0.29 wt.%, The balance is Mg.

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

1) Alloy smelting and casting: the raw materials used are pure magnesium ingots, pure zinc ingots, Mg-25 wt.%Y master alloys, Mg-20 wt.%Ce master alloys, and Mg-20 wt.%Ca master alloys. First, preheat the raw materials and crucible at 200°C and keep it warm for 1 hour. Then, under the protection of CO ₂ and SF ₆ mixed gas (the ratio is 99:1), put the magnesium ingot into the crucible and heat it to 700°C for melting. Raise the temperature to 720°C, put the zinc ingot and the master alloy into the molten magnesium, stir for 2-5 minutes after melting to make the composition uniform, and let it 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 salt water for water cooling to prepare the required magnesium alloy ingot;

2) machining: with embodiment 1

3) homogenization: with embodiment 1

4) hot extrusion: with embodiment 1

Example 3:

A new low-cost high-strength Mg-Zn-Y-Ce-Ca magnesium alloy, including the following components by mass percentage: Zn5.1wt.%, Y 0.37 wt.%, Ce 0.17 wt.%, Ca 0.61 wt.%, The balance is Mg. The method of alloy smelting-machining-homogenization-hot extrusion to obtain the magnesium alloy of this example is the same as that of Example 2.

Example 4:

A new type of low-cost medium-high-strength Mg-Zn-Y-Ce-Ca magnesium alloy, including the following components by mass percentage: Zn 5.1wt.%, Y 0.36 wt.%, Ce 0.19 wt.%, Ca 0.28 wt.%, The balance is Mg.

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

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

2) machining: with embodiment 2;

3) homogenization: with embodiment 2;

4) Hot extrusion: Remove the surface scale from the material in step 3), preheat the extrusion die at 350°C for 1 hour, and extrude at 300°C with an extrusion ratio of 25:1 and an extrusion speed of 0.6 ~1.2 m/min, a magnesium alloy rod with a diameter of 16 mm was obtained.

Mechanical performance 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 tensile test at room temperature on a CMT-5105 universal testing machine. The test results are shown in Table 1.

Table 1 Room temperature mechanical properties of low-cost medium-high strength magnesium alloys of the present invention

It can be seen from Table 1 that after adding an appropriate amount of Ca to the alloy, the mechanical properties of the alloy are greatly improved after extrusion treatment, and the appropriate elongation can be maintained. The yield strength in Example 3 can reach 321MPa, which is significantly higher than that of the ZK60 magnesium alloy. The tensile strength can reach 361MPa, and the elongation rate is 10.4%. It can be used as 3C products and lightweight structural materials for rail transit parts.

Comparing Figure 1, the organization in Figure 2 and Figure 3 is clearly 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. Distributed along the extrusion direction, these second phases can promote the formation of dynamic recrystallization, and the elements dissolved into the matrix will be dynamically precipitated during the extrusion process. In the dispersed distribution matrix, the fine second phase particles and dispersed phase can pin the crystal boundary, hindering the growth of recrystallized grains. It can be seen from Figure 3 that there are many broken second phases in the alloy, and the energy spectrum analysis shows Mg-Zn-Y I phase, Mg-Zn-Ce phase, and Ca2Mg6Zn3 phase. These second phases can pin the dislocation movement and improve the mechanical properties of the alloy.

Finally, it is noted that the above embodiments are only used to illustrate the technical solutions of the present invention without limitation. 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 carried out Modifications or equivalent replacements that do not depart from the spirit and scope of the technical solution of the present invention shall be covered by the claims of the present invention.

Claims (2)

1. a kind of low-cost high-strength Mg-Zn-Y-Ce-Ca magnesium alloy, which is characterized in that ingredient percent are as follows: Zn 5.0 ~ 6.0 wt.%, Y 0.15 ~ 0.45 wt.%, Ce 0 ~ 1.0 wt.% of 0.15 ~ 0.35 wt.%, Ca, remaining is for Mg and unavoidably Impurity.

2. the preparation method of low-cost high-strength Mg-Zn-Y-Ce-Ca magnesium alloy as described in claim 1: including walking as follows It is rapid:

1) melting: matching raw material by the component, raw materials used for conjunction among pure magnesium ingot, pure zinc ingot, Mg-Y intermediate alloy, Mg-Ce Gold, Mg-Ca intermediate alloy, first preheat raw material and crucible at 200 DEG C, 1h are kept the temperature, later in CO₂And SF₆Mixed gas is protected Under shield, magnesium ingot is put into crucible and is heated to 700 DEG C of fusings, to whole fusings, temperature is risen to 720 DEG C, by zinc ingot metal and intermediate conjunction Gold is put into magnesium melt, is stirred 2 ~ 5 minutes after fusing, is kept its ingredient uniform, 10 ~ 20 minutes is stood at 720 DEG C, after standing Dross on surface of fusant is salvaged, crucible is taken out when temperature is down to 700-710 DEG C and is put into water cooling in salt water, required magnesium is prepared and closes Golden ingot casting；

2) it machines: cylinder size being squeezed according to extruder, by above-mentioned ingot casting railway carriage, is sawn to suitable dimension；

3) it homogenizes: the magnesium alloy ingot prepared in step 2) is covered with graphite, 10 ~ 12h, Zhi Hou are kept the temperature at 350 DEG C 6h is kept the temperature at 400 DEG C, takes out quenching, the material after obtaining Homogenization Treatments；

4) hot extrusion: the material in step 3) is removed into surface scale and extrusion die preheats 1h at 350 DEG C, at 300 DEG C It is squeezed at ~ 350 DEG C, extrusion ratio 25:1, extrusion speed is 0.6 ~ 1.2 m/min, obtains magnesium alloy rod.