CN107964602B - Effective method for improving plastic forming capability of high-strength Mg-Gd-Y-Nd-Zr magnesium alloy - Google Patents

Abstract

The invention relates to the field of plastic enhancement of high-strength magnesium alloys, in particular to a method for effectively utilizing element Li to improve the plastic forming ability of high-strength Mg-Gd-Y-Nd-Zr magnesium alloys, which solves the problem of extremely poor high-strength plasticity. Under the premise of keeping the relative contents of all elements in the alloy unchanged, by adding 5-20% Li element by weight, a β-Li phase with strong plastic deformation ability is formed in the alloy, and the formation of β-Li phase is controlled. The volume fraction of Li phase (20-90%), a lithium-containing Mg-Gd-Y-Nd-Zr alloy with high strength and good plasticity is prepared, which is processed into a sheet by alloy melting and subsequent hot rolling. Simple and convenient operation. The tensile strength of the material of the present invention under as-cast conditions is σ _b =120-250MPa, the yield strength is σ _0.2 =80-150MPa, the elongation is δ=10-30%, and the density is 1.50-1.89g/cm ³ , And the plate will not appear edge cracking after being deformed by 40% of the rolling amount at room temperature.

Description

An effective method to improve the plastic formability of high-strength Mg-Gd-Y-Nd-Zr magnesium alloys

technical field

The invention relates to the field of plastic enhancement of high-strength magnesium alloys, in particular to a method for effectively utilizing element Li to improve the plastic forming ability of high-strength Mg-Gd-Y-Nd-Zr magnesium alloys.

Background technique

Among all metal structural materials, magnesium alloy has the lowest density, which is 2/3 of aluminum alloy and 1/4 of stainless steel. If magnesium alloy materials can replace most of stainless steel and aluminum alloys in aircraft and vehicles, it can not only achieve the purpose of reducing its own weight and speed, but also effectively solve a series of problems related to energy saving and environmental protection. At the same time, magnesium alloys also have the advantages of high specific strength and specific stiffness, strong resistance to high-energy particle penetration, good electromagnetic shielding performance, good damping performance, and excellent machinability, which make magnesium alloys in aerospace and automotive high-tech fields. potential application prospects.

However, compared with traditional metal structural materials, the absolute engineering strength of magnesium alloys is relatively low, and it is difficult to meet the requirements of the bearing capacity of engineering components, which seriously restricts the application and further development of the alloys. In recent years, researchers have found that the addition of rare earth elements can significantly strengthen magnesium alloys, and the maximum tensile strength of Mg-Gd-Y-Nd-Zr alloys can reach more than 400MPa, which is basically equivalent to that of medium-strength aluminum alloys. However, the ductility of Mg-Gd-Y-Nd-Zr magnesium alloy is extremely poor, and its elongation is difficult to exceed 5%, resulting in very limited plastic forming ability of the alloy.

Early studies have shown that the addition of elemental Li can promote the formation of β-Li phase in magnesium alloys, which can significantly improve the plastic formability of the alloys. It can be predicted that if a certain weight percentage of Li element is added to the high-strength Mg-Gd-Y-Nd-Zr magnesium alloy to form a certain volume fraction of β-Li phase, the plastic forming ability of the alloy can be effectively improved, and the extreme It will greatly promote and broaden the practical engineering application of high-strength magnesium alloys.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an effective method for improving the plastic forming ability of high-strength Mg-Gd-Y-Nd-Zr magnesium alloys. element, to form a β-Li phase with strong plastic deformation ability in the alloy, and to control the volume fraction of the formed β-Li phase to prepare a lithium-containing Mg-Gd-Y-Nd-Zr with high strength and good plasticity Alloy, to solve the problem of poor plastic forming ability of high-strength magnesium alloy.

The technical scheme of the present invention is:

An effective method for improving the plastic forming ability of high-strength Mg-Gd-Y-Nd-Zr magnesium alloy, the lithium content in the alloy is 5-20%, and the volume fraction of the formed β-Li phase is 20-90%.

In the effective method for improving the plastic forming ability of high-strength Mg-Gd-Y-Nd-Zr magnesium alloy, the gadolinium content is 5-10%; the yttrium content is 3-8%; the neodymium content is 0.5-10% by weight. 2%; Zirconium content is 0.3-1.0%; Lithium content is 5-20%; Magnesium balance.

In the effective method for improving the plastic forming ability of the high-strength Mg-Gd-Y-Nd-Zr magnesium alloy, the tensile strength of the alloy under the as-cast condition is σ _b =120～250MPa; the yield strength is σ _0.2 =80～ 150MPa; elongation δ=10～30%; density of alloy is 1.50～1.89g/cm ³ .

According to the effective method for improving the plastic forming ability of the high-strength Mg-Gd-Y-Nd-Zr magnesium alloy, the alloy plate does not appear edge cracks after being deformed by 40% of the rolling amount.

The described effective method for improving the plastic formability of high-strength Mg-Gd-Y-Nd-Zr magnesium alloys is to melt Mg-Gd-Y-Nd-Zr alloys and pure lithium ingots in a vacuum smelting furnace, and place them in an argon smelting furnace. It is carried out under the condition of gas shielding, and after being kept at a temperature of 740 to 780° C. for 3 to 5 hours, it is cast and formed in a furnace to obtain an ingot.

The effective method for improving the plastic forming ability of the high-strength Mg-Gd-Y-Nd-Zr magnesium alloy is that the ingot is subjected to a homogenization treatment at a temperature of 300-400 DEG C for 6-10 hours, and is tightly wrapped with aluminum foil, In order to prevent the possible combustion of the alloy due to high temperature oxidation.

The effective method for improving the plastic forming ability of the high-strength Mg-Gd-Y-Nd-Zr magnesium alloy is to perform plastic processing on the homogenized ingot at a temperature ranging from room temperature to 350°C.

In the effective method for improving the plastic forming ability of the high-strength Mg-Gd-Y-Nd-Zr magnesium alloy, the plastic processing is extrusion, rolling or forging with different deformation ratios.

The design idea of the present invention is:

含量为5～20％；镁余量)，使合金中形成一定体积分数的β-Li相(β-Li相的体积分数优选为60～90％)。经均匀化处理后，使合金中粗大共晶组织得以固溶，这样的作用在于：消除凝固过程中形成大尺寸共晶组织造成的应力集中，极大的发挥出β-Li相具有的塑性变形协调能力，有效避免了塑性加工变形过程中板材的边裂现象，最终显著提高了合金的塑性成型能力。In the present invention, a certain weight percentage of Li element (preferably 8-12%) is added to the high-strength Mg-Gd-Y-Nd-Zr magnesium alloy reasonably, and the relative content of other elements in the alloy is kept unchanged (according to By weight percentage, the content of gadolinium (Gd) is 5-10%; the content of yttrium (Y) is 3-8%; the content of neodymium (Nd) is 0.5-2%; the content of zirconium (Zr) is 0.3-1.0%;

The content is 5-20%; magnesium balance), so that a certain volume fraction of β-Li phase is formed in the alloy (the volume fraction of β-Li phase is preferably 60-90%). After the homogenization treatment, the coarse eutectic structure in the alloy can be solid-dissolved. This effect is to eliminate the stress concentration caused by the formation of large-size eutectic structure during the solidification process, and greatly exert the plastic deformation of the β-Li phase. The coordination ability effectively avoids the edge cracking of the plate during the plastic deformation process, and finally significantly improves the plastic forming ability of the alloy.

The advantages and beneficial effects of the present invention are:

1. By adopting this method in the present invention, the enhancement of the plastic deformation coordination ability of the magnesium alloy by the element Li can be fully utilized, the plastic processing and forming ability of the magnesium alloy is significantly improved, and the practical engineering application of the magnesium alloy is effectively promoted.

2. The present invention adopts this method to obtain a magnesium alloy material with low density, high strength and strong plastic forming ability, which is especially suitable for the material requirements of light weight, high strength and high toughness.

3. The equipment used in the present invention is simple, the cost is low, and the operation of the processing technology is simple and convenient.

Description of drawings

Figure 1 XRD phase analysis results of high strength Mg-7%Gd-5%Y-1%Nd-0.5%Zr magnesium alloys (Comparative Example 1 and Example 1) with and without Li. In the figure, the abscissa 2θ is the diffraction angle (degree), and the ordinate Intensity is the intensity (a.u.)

Figure 2 Microstructure photographs of high-strength Mg-7%Gd-5%Y-1%Nd-0.5%Zr magnesium alloys with and without Li (Comparative Example 1 and Example 1). in,

(a) Comparative Example 1 alloy Mg-7%Gd-5%Y-1%Nd-0.5%Zr; (b) Example 1 alloy Mg-7%Gd-5%Y-1%Nd-0.5%Zr- 10% Li.

Fig. 3(a)-Fig. 3(b) Plastic deformation of high-strength Mg-7%Gd-5%Y-1%Nd-0.5%Zr magnesium alloys with and without Li (Comparative Example 1 and Example 1) Ability comparison. Among them, Fig. 3(a) Comparative Example 1 Mg-7%Gd-5%Y-1%Nd-0.5%Zr alloy plate with a rolling amount of 12% has serious edge cracks on the side surface; Fig.3(b) Example 1 The side surface of the Mg-7%Gd-5%Y-1%Nd-0.5%Zr-10%Li alloy plate with a rolling amount of 40% has no edge cracking phenomenon.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments. It should be noted that the given 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 specific embodiments implemented below.

Comparative Example 1

In this embodiment, the effective method to improve the plastic forming ability of high-strength Mg-Gd-Y-Nd-Zr magnesium alloy is as follows:

Ⅰ), the composition of magnesium-lithium alloy used

Using high-strength Mg-7%Gd-5%Y-1%Nd-0.5%Zr alloy, its chemical composition (weight percentage) is: gadolinium content is 7%; yttrium content is 5%; neodymium content is 1% ; Zirconium content is 0.5%; Magnesium balance.

Ⅱ), alloy smelting

Alloy smelting is carried out in a vacuum smelting furnace under the protection of argon gas, and after holding for 4 hours at a temperature of 770 ° C, casting is carried out in the furnace.

Ⅲ), homogenization treatment

The high-strength Mg-7%Gd-5%Y-1%Nd-0.5%Zr alloy was kept at 400°C for 8 hours and tightly wrapped with aluminum foil to prevent the alloy from burning due to high temperature oxidation.

Ⅳ), plastic deformation

Under the condition of room temperature, the alloy after homogenization is rolled and formed, and the rolling reduction is 12%.

Ⅴ), microstructure characterization

The preparation process of the sample for tissue observation is as follows: the surface is smoothed with No. 1000 silicon carbide water abrasive paper, and then mechanically polished with oil-based diamond abrasive paste. The XRD results show that the sample of Comparative Example 1 mainly contains α-Mg and Mg5Gd phases, and the corresponding photos are shown in Figure 1. The optical observation results show that there is no β-Li phase in the sample of Comparative Example 1, and the corresponding photo is shown in Figure 2(a).

Ⅵ), mechanical properties test

The room temperature tensile properties of the alloy samples are plate-shaped, with a standard length of 25 mm, a width of 5 mm, and a thickness of 4 mm. The strain rate of the tensile test was 1×10 ^-3 s ^-1 , and the tensile test was carried out on an MTS (858.01M) tensile-torsion testing machine. The corresponding tensile properties of the alloy were determined. The yield and tensile strength were 148MPa and 148MPa, respectively. 220MPa, elongation 1%, listed in Table 1.

Ⅶ), plastic forming ability

When the rolling amount is 12%, serious edge cracks appear on the side of the high-strength Mg-7%Gd-5%Y-1%Nd-0.5%Zr alloy sheet, as shown in Figure 3(a).

Example 1

In this embodiment, the effective method to improve the plastic forming ability of high-strength Mg-Gd-Y-Nd-Zr magnesium alloy is as follows:

Ⅰ), the used lithium-containing Mg-7%Gd-5%Y-1%Nd-0.5%Zr-10%Li alloy composition

Using lithium-containing high-strength Mg-7%Gd-5%Y-1%Nd-0.5%Zr-10%Li alloy, its chemical composition (weight percentage) is: gadolinium content is 7%; yttrium content is 5% %; Neodymium content is 1%; Zirconium content is 0.5%; Lithium content is 10%; Magnesium balance.

Ⅱ), alloy smelting

The Mg-Gd-Y-Nd-Zr alloy and pure lithium ingot were melted in a vacuum smelting furnace, and the alloy was smelted under the protection of argon. .

Ⅲ), homogenization treatment

The high-strength Mg-7%Gd-5%Y-1%Nd-0.5%Zr-10%Li alloy was kept at 400℃ for 8 hours and tightly wrapped with aluminum foil to prevent the alloy from burning due to high temperature oxidation.

Ⅳ), plastic deformation

Under the condition of room temperature, the alloy after homogenization is rolled and formed, and the rolling reduction is 40%.

Ⅴ), microstructure characterization

The preparation process of the sample for tissue observation is as follows: the surface is smoothed with No. 1000 silicon carbide water abrasive paper, and then mechanically polished with oil-based diamond abrasive paste. The XRD results show that the sample of Example 1 mainly contains β-Li, α-Mg and Mg5Gd phases, and the corresponding photos are shown in Figure 1. The optical observation results show that the volume fraction of the quasicrystal phase formed in the sample of Example 1 is 75%, and the corresponding photo is shown in Figure 2(b).

Ⅵ), mechanical properties test

The tensile specimen processing and tensile properties testing methods are as follows: the room temperature tensile properties of the alloy samples are plate-shaped, and the standard length of the specimen is 25 mm, the width is 5 mm, and the thickness is 4 mm. The strain rate of the tensile test was 1×10 ^-3 s ^-1 , and the tensile test was carried out on an MTS (858.01M) tensile-torsion testing machine to determine the corresponding tensile properties of the alloy. The yield and tensile strengths of the alloy samples of Example 1 were measured to be 105 MPa and 195 MPa, respectively, and the elongation was 24%, which are listed in Table 1.

Ⅶ), plastic forming ability

When the rolling amount is 40%, the high-strength Mg-7%Gd-5%Y-1%Nd-0.5%Zr-10%Li alloy sheet has no side cracking phenomenon, as shown in Figure 3(b).

Example 2

In this embodiment, the effective method to improve the plastic forming ability of high-strength Mg-Gd-Y-Nd-Zr magnesium alloy is as follows:

Ⅰ), the used lithium-containing Mg-9%Gd-6%Y-1.5%Nd-0.5%Zr-10%Li alloy composition

Using lithium-containing high-strength Mg-9%Gd-6%Y-1.5%Nd-0.5%Zr-10%Li alloy, its chemical composition (weight percentage) is: gadolinium content is 9%; yttrium content is 6% %; Neodymium content is 1.5%; Zirconium content is 0.5%; Lithium content is 10%; Magnesium balance.

Ⅱ), alloy smelting

Same as Example 1.

Ⅲ), homogenization treatment

Same as Example 1.

Ⅳ), plastic deformation

Same as Example 1.

Ⅴ), microstructure characterization

The tissue observation method is the same as that of Example 1. XRD results show that the sample in Example 2 mainly contains β-Li, α-Mg and Mg5Gd phases. The optical observation results show that the volume fraction of the quasicrystal phase formed in the sample of Example 2 is 75%.

Ⅵ), mechanical properties test

Tensile specimen processing and tensile properties testing methods are the same as in Example 1. The yield and tensile strengths of the alloy samples of Example 2 were measured to be 135 MPa and 233 MPa, respectively, and the elongation was 21%, which are listed in Table 1.

Ⅶ), plastic forming ability

When the rolling amount is 40%, the high-strength Mg-9%Gd-6%Y-1.5%Nd-0.5%Zr-10%Li alloy sheet has no side cracking phenomenon.

In the present invention, the mechanical property data of the high-strength Mg-Gd-Y-Nd-Zr alloys (Comparative Example 1, Example 1 and Example 2) with and without Li element are shown in Table 1.

Table 1

Sample status Yield Strength (MPa) Tensile strength (MPa) Elongation (%) Density (g/cm³) Comparative Example 1 Sample 148 220 1 1.93 Example 1 Sample 105 195 twenty four 1.56 Example 2 Sample 135 233 twenty one 1.72

The results of the examples show that the use of the present invention can effectively utilize the element Li, which can significantly improve the plastic forming ability of the high-strength Mg-Gd-Y-Nd-Zr magnesium alloy, solve the problem of poor plasticity of the magnesium alloy, and at the same time, the alloy retains relatively high plasticity. The high engineering strength broadens the practical engineering application of such high-strength magnesium alloys.

Claims (4)

1. an effective method for improving the plastic forming ability of high-strength Mg-Gd-Y-Nd-Zr magnesium alloy, it is characterized in that: by weight percentage, gadolinium content in the alloy is 5～7%; yttrium content is 5～8 %; the content of neodymium is 0.5-2%; the content of zirconium is 0.3-1.0%; the content of lithium is 8-12%; the balance of magnesium, the volume fraction of the formed β-Li phase is 20-90%; The tensile strength of the alloy under as-cast condition is σ _b =120～250MPa; the yield strength is σ _0.2 =80～150MPa; the elongation is δ=10～30%; the density of the alloy is 1.50～1.89g/cm ³ ; The Mg-Gd-Y-Nd-Zr alloy and pure lithium ingot are melted in a vacuum smelting furnace and carried out under the protection of argon. Casting is performed to obtain ingots; The ingot is homogenized at a temperature of 300-400°C for 6-10 hours, and is tightly wrapped with aluminum foil to prevent possible combustion of the alloy due to high-temperature oxidation. 2. according to the effective method of improving the plastic forming ability of high-strength Mg-Gd-Y-Nd-Zr magnesium alloy according to claim 1, it is characterized in that: the alloy plate does not have edge cracks after the deformation of 40% rolling amount Phenomenon. 3. The effective method for improving the plastic formability of high-strength Mg-Gd-Y-Nd-Zr magnesium alloys according to claim 1, characterized in that: under the temperature condition of room temperature to 350 ℃, the homogenized cast The ingot is processed plastically. 4. The effective method for improving the plastic forming ability of high-strength Mg-Gd-Y-Nd-Zr magnesium alloys according to claim 3, wherein the plastic working treatment is extrusion, rolling or forging with different deformation ratios.

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