CN108179335A - A kind of high intensity low density hcp+bcc double structures magnesium lithium alloy bar and preparation method thereof - Google Patents

Abstract

The invention discloses a kind of high intensity low density hcp+bcc double structures magnesium lithium alloy bar, raw materials by weight is as follows：Li：6.1 10.2%, Al：4.6 5.8%, Zn：1.5 2.3%, Y：0.1 0.6%, surplus is Mg and its impurity element, and impurity element includes Ca, Fe, Cu, Ni, and total amount is less than 0.2%, wherein Fe≤0.04%, Ca≤0.03%.The present invention is added to micro Y element and forms Al2Y hardening constituents with matrix Mg elements to improve the intensity of alloy by the Proper Match of alloying element type and proportionate relationship；The present invention is added in melt using the mode of Mg Y intermediate alloys and carries out melting, reduces cost of alloy, is conducive to industrialized production；On the one hand the present invention reduces the complexity of experimental implementation, on the other hand improves melt purification and yield of alloy using semicontinuous casting technique has been carried out under non-vacuum condition, lay a good foundation for later high intensity super-light Mg-Li alloy.

Description

A kind of high-strength low-density hcp+bcc double-structure magnesium-lithium alloy rod and preparation method thereof

technical field

The invention relates to the field of dropped magnesium-lithium alloy rods, in particular to a high-strength low-density hcp+bcc double-structure magnesium-lithium alloy rod and a preparation method thereof.

Background technique

Magnesium-lithium alloy is currently the lightest alloy material on the earth, with a density of 1.35-1.65g/cm3, which is 1/3-1/2 of the density of ordinary aluminum alloys and 1/4-1/3 of the density of ordinary magnesium alloys. Magnesium-lithium alloy has many advantages such as low density, high specific strength, high specific stiffness, good resistance to high-energy particle penetration, excellent electromagnetic shielding performance, good welding performance and excellent cold forming ability, so it is widely used in In the fields of aviation, aerospace, military, communication, 3C electronic products and other fields, it is known as "green engineering material in the 21st century". In recent years, the world's industrial production has required energy saving, emission reduction, energy consumption reduction, and environmental protection, which has stimulated the extensive development potential of magnesium-lithium alloys in the future. At present, the urgent demand for lightweight materials in many fields such as aerospace in my country provides more opportunities and challenges for the development and application of magnesium-lithium alloys. When lithium is added to the magnesium alloy, the density of the alloy decreases gradually, the plasticity increases gradually, but the strength decreases gradually. The disadvantages of magnesium-lithium alloys such as low strength, high development cost, and complicated operation limit the application of magnesium-lithium alloys in the national economy. Therefore, it is of great significance to prepare high-strength ultra-light magnesium-lithium alloys and develop a simple and effective preparation process suitable for industrial production.

With the continuous addition of Li elements in magnesium, the matrix structure of magnesium-lithium alloys is also constantly changing. When the Li content is lower than 5.7wt.%, the alloy matrix is mainly composed of α-Mg, when the Li content is 5.7wt.%-10.3wt.%, the alloy matrix becomes α+β dual-phase structure, when the Li content is high At 10.3wt.%, the alloy matrix completely transformed into β-Li single-phase structure. Alloying elements commonly used in magnesium-lithium alloys include Al, Zn and other elements. Studies have shown that Al has a significant strengthening effect on magnesium-lithium alloys. When the Al content is lower than 6wt.%, the strength increases very obviously, but when it is higher than 6wt.%, the strength trend is flat, so the addition of Al content should be Less than 6wt.%. Zn element also has a similar strengthening effect on magnesium-lithium alloys. Under the same mass, the strengthening effect of Zn element is not as obvious as that of Al element. However, considering the low density of the alloy, the content of Zn element should not be too high. Rare earth elements are also strengthening elements for magnesium-lithium alloys. With the addition of Y element, Mg and Y in the alloy will form a Mg24Y5 strengthening phase. After subsequent heat treatment, the Mg24Y5 phase is gradually dispersed and spheroidized, and the solid solubility in the β-Li phase is also increasing, which greatly improves the The strength of magnesium-lithium alloys. In the patent application number 201110266610.2, a high-plastic magnesium-lithium alloy containing Y element and its preparation method are announced. Although the high plasticity of the alloy is guaranteed, the strength of the alloy is low, which is 145-175MPa. This inevitably limits the application value of magnesium-lithium alloys.

Contents of the invention

The object of the present invention is to solve the shortcomings in the prior art, and propose a high-strength low-density hcp+bcc double-structure magnesium-lithium alloy rod and a preparation method thereof.

In order to achieve the above object, the present invention adopts the following technical solutions:

A high-strength and low-density hcp+bcc double-structure magnesium-lithium alloy rod, the raw materials of which are as follows by weight percentage: Li: 6.1-10.2%, Al: 4.6-5.8%, Zn: 1.5-2.3%, Y: 0.1-0.6% , the balance is Mg and its impurity elements, the impurity elements include Ca, Fe, Cu, Ni, the total amount is less than 0.2%, wherein Fe≤0.04%, Ca≤0.03%.

The present invention also provides a method for preparing a high-strength low-density hcp+bcc double-structure magnesium-lithium alloy bar, comprising the following steps:

S1: Prepare pure magnesium ingots, pure lithium strips, pure aluminum ingots, pure zinc ingots and Mg-25% Y master alloy as raw materials;

S2: After the alloy is completely melted at 720°C, a magnesium-lithium alloy ingot is prepared by a semi-continuous casting process under the condition of feeding a protective gas;

S3: Machining and homogenizing heat treatment of the magnesium-lithium alloy ingot;

S4: performing single-pass constant temperature reverse extrusion on the homogenized magnesium-lithium alloy ingot to obtain magnesium-lithium alloy rods;

S5: Heat the magnesium-lithium alloy rod to 270-290°C for at least 30 hours to complete the solution treatment, water-cool to room temperature, and then perform room temperature polishing to obtain a high-strength and low-density hcp+bcc double-structure magnesium-lithium alloy rod.

Preferably, the protective gas is a mixed gas of argon and sulfur hexafluoride in a ratio of 1:3.

Preferably, during the casting process, the applied low-frequency electromagnetic frequency is 100 Hz, the intensity is 41000 AT, and the casting speed is 350 mm/min.

Preferably, the constant temperature extrusion temperature is 200-250° C., and the extrusion speed is 1.3-1.8 mm/s.

Compared with prior art, the beneficial effect of the present invention is:

1. The present invention increases the strength of the alloy by adding a small amount of Y element and forming an Al2Y strengthening phase with the matrix Mg element through the reasonable matching of the type and proportion of the alloy element;

2. What the present invention adopts is that the mode of Mg-Y master alloy is added in the melt and smelts, has reduced alloy cost, is conducive to industrialized production;

3. The present invention uses a semi-continuous casting process under non-vacuum conditions. On the one hand, it reduces the complexity of the experimental operation, and on the other hand, it improves the purity of the melt and the yield of the alloy. Light magnesium lithium alloy laid the foundation;

4. The extrusion process of the present invention adopts single-pass constant temperature reverse extrusion. During the reverse extrusion process, the temperature of the extrusion cylinder is kept constant, which can not only reduce the occurrence of macroscopic and microscopic defects of the rod, but also increase the effective extrusion length of the rod. By changing the extrusion temperature and speed, the recrystallization structure of the alloy can be adjusted from time to time, thereby greatly improving the strength and plasticity of the sheet;

5. The magnesium-lithium alloy of the present invention undergoes solid solution treatment at low temperature for a long time, and the MgAlLi2 and AlLi phases can greatly compensate for the softening effect of the bcc-Li structure on the alloy through the solid solution behavior in the bcc-Li structure, thereby greatly improving the strength of the alloy . The solid solution temperature is 200°C-320°C, and the holding time is 20-50h. The results also show that the heat resistance of the magnesium-lithium alloy is also improved;

6. The present invention improves the strength of the alloy through the solid solution strengthening of the Zn element;

7. The present invention considers the low density of the alloy, and precisely regulates the contents of Al, Zn, and Y elements;

8. The preparation process of the present invention is clear and clear, easy to operate, and is conducive to industrial production. The prepared magnesium-lithium alloy rod has high strength and good shape. The tensile strength at room temperature is 230-300MPa, and the elongation 10%-25%.

Description of drawings

Fig. 1 is a structural representation of the present invention;

Fig. 2 is the scanning picture of the extruded state of magnesium-lithium alloy of the present invention;

Fig. 3 is the scanning picture of magnesium-lithium alloy annealed state of the present invention;

Fig. 4 is a picture of the mechanical properties of the magnesium-lithium alloy of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Example 1

A high-strength and low-density hcp+bcc double-structure magnesium-lithium alloy rod, the raw materials of which are as follows by weight percentage: the chemical composition and weight percentage of the magnesium-lithium alloy are: Li: 8.8%, Al: 5.7%, Zn: 1.9%, 0.5% %Y, inevitable Ca, Fe, Cu, Ni and other impurity elements, the total amount is less than 0.2%, of which Fe≤0.04%, Ca≤0.03%. The rest is Mg.

Dry each raw material at 200±5°C for 30 minutes, then place the pure magnesium ingot in a smelting furnace and raise the temperature to 720±5°C. After the metal magnesium is completely melted, a magnesium melt is formed, and then the dried Mg-Y is placed in the middle The alloy, pure aluminum and pure zinc are placed in the magnesium melt in sequence, and the covering agent is sprayed to cover the surface of the magnesium melt, and the temperature is controlled at 720°C and stirred;

Under the condition of feeding protective gas, the temperature of the melt is lowered to 670°C, and the pure lithium strip wrapped in aluminum foil is pressed into the melt with a bell jar, and then the alloy melt is stirred. After all the metals in the crucible are melted, add refining The agent continued to stir up and down for 15s;

The alloy melt is slowly poured into the crystallizer through the spout below the melting furnace wall, and finally the magnesium-lithium alloy ingot is obtained through the semi-continuous casting process. During the semi-continuous casting process, the applied low-frequency electromagnetic frequency is 100Hz, and the strength 41000AT, casting speed 350mm/min;

Machining and homogenization heat treatment of magnesium-lithium alloy ingots, the homogenization temperature is 250±5℃, and the time is 1h;

The homogenized magnesium-lithium alloy ingot is subjected to a single-pass constant temperature reverse extrusion process to obtain a magnesium-lithium alloy rod, the extrusion temperature is 250 ° C, and the extrusion speed is 1.5mm/s;

Heat the magnesium-lithium alloy rod to 280°C for 48 hours to complete the solution treatment, water-cool to room temperature, and then perform room temperature polishing to obtain a high-strength and low-density hcp+bcc double-structure magnesium-lithium alloy rod;

The magnesium-lithium alloy rod is heated to 280°C for 48 hours to complete the solution treatment, cooled to room temperature, and then polished at room temperature to obtain a high-strength and low-density dual-phase structure magnesium-lithium alloy material; the alloy density is 1.49g/cm3, Tensile strength 238.7MPa, elongation 21.2%. The XRD pattern of the alloy is shown in Figure 1, the scanning image of the alloy in the extruded state is shown in Figure 2, the scanning image of the alloy after heat treatment is shown in Figure 3, and the mechanical properties of the final alloy in the extruded state and heat treatment state are shown in Figure 4 shown.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, any person familiar with the technical field within the technical scope disclosed in the present invention, according to the technical solution of the present invention Any equivalent replacement or change of the inventive concepts thereof shall fall within the protection scope of the present invention.

Claims (5)

1. a kind of high intensity low density hcp+bcc double structures magnesium lithium alloy bar, it is characterised in that：Its raw materials by weight is such as Under：Li：6.1-10.2%, Al：4.6-5.8%, Zn：1.5-2.3%, Y：0.1-0.6%, surplus be Mg and its impurity element, Impurity element includes Ca, Fe, Cu, Ni, and total amount is less than 0.2%, wherein Fe≤0.04%, Ca≤0.03%.

2. a kind of preparation method of high intensity low density hcp+bcc double structures magnesium lithium alloy bar described in claim 1, feature It is：Include the following steps：

S1：Prepare pure magnesium ingot, pure lithium band, fine aluminium ingot, pure zinc ingot and Mg-25%Y intermediate alloys as raw material；

S2：It is prepared after alloy all fusing in the case where being passed through protection gas by semicontinuous casting technique at 720 DEG C Go out magnesium lithium alloy ingot blank；

S3：Magnesium lithium alloy ingot casting is subjected to mechanical processing and homogenizes heat treatment；

S4：Magnesium lithium alloy ingot casting after Homogenization Treatments is subjected to single pass constant temperature reverse extrusion, obtains magnesium lithium alloy bar；

S5：Magnesium lithium alloy bar is heated to 270-290 DEG C of heat preservation at least 30h and completes solution treatment, water cooling to room temperature, Ran Houjin Row room temperature polishing treatment obtains high intensity low density hcp+bcc double structure magnesium lithium alloy bars.

3. a kind of preparation method of high intensity low density hcp+bcc double structures magnesium lithium alloy bar according to claim 2, It is characterized in that：Mixed gas of the protection gas for argon gas and sulfur hexafluoride, its ratio be 1：3.

4. the preparation method of high intensity low density hcp+bcc double structures magnesium lithium alloy bar according to claim 2, feature It is：In the casting process, the low frequency electromagnetic frequency of application is 100Hz, intensity 41000AT, casting speed 350mm/ min。

5. a kind of preparation method of high intensity low density hcp+bcc double structures magnesium lithium alloy bar according to claim 2, It is characterized in that：The constant temperature extrusion temperature is 200-250 DEG C, extrusion speed 1.3-1.8mm/s.