CN111041311A

CN111041311A - Rare earth magnesium alloy with low cost and high performance and preparation technology thereof

Info

Publication number: CN111041311A
Application number: CN201911406569.7A
Authority: CN
Inventors: 刘轲; 郭成龙; 杜文博; 李淑波; 王朝辉; 杜宪
Original assignee: Beijing University of Technology
Current assignee: Beijing University of Technology
Priority date: 2019-12-31
Filing date: 2019-12-31
Publication date: 2020-04-21

Abstract

A rare earth magnesium alloy with low cost and high performance and a preparation technology thereof belong to the advanced manufacturing technology of metal materials. The alloying element and the content thereof in the alloy plate are mainly rare earth element Gd, and the mass percent content is less than or equal to 6 percent; the mass percent of the rare earth element Er is less than or equal to 2.0 percent, the total mass percent of the rare earth in the alloy is less than or equal to 8.0 percent, the mass percent of Zr is less than or equal to 1.0 percent, and the balance is Mg. Under the condition of the invention, the rolling temperature is 300-450 ℃, the rolling reduction reaches 75% or more, the thickness of the obtained magnesium metal plate is 1.0-1.5mm, the yield strength can reach 200-350 MPa, the tensile strength can reach 260-370 MPa, the elongation is 2-10%, and the chain-shaped structure in the alloy is the main reason for improving the alloy performance. The alloy is convenient to produce, high in preparation efficiency and short in process flow, and is a magnesium alloy plate with great application prospect.

Description

Rare earth magnesium alloy with low cost and high performance and preparation technology thereof

Technical Field

The invention relates to a rare earth magnesium alloy material with low cost and high strength and a preparation process technology, belongs to an advanced manufacturing technology of metal materials, and particularly relates to a forming process for obtaining a high-strength rare earth magnesium metal plate.

Background

The magnesium alloy has excellent performance, the density of the magnesium alloy is about 1.8g/cm3, only 2/3 of aluminum and 1/4 of steel have the characteristics of light specific gravity, high specific strength and specific rigidity, good shock absorption performance, easy heat conduction, good electromagnetic shielding performance, easy recycling and the like, can meet the requirement of the automobile and aerospace field on material lightweight, and the annual growth rate of the magnesium alloy in the world is up to 20 percent in recent years, mainly because the magnesium alloy usage in the world is increased due to the sharp demand of industries such as automobiles and portable electronic products. It can be said that magnesium alloy will be widely applied in fields of modern automobiles, aerospace, national defense and portable electronic products in the 21 st century, and is a green engineering material in the 21 st century. But at the same time, because magnesium is in a typical close-packed hexagonal structure, the magnesium has poor processability at a lower temperature, which causes great difficulty in preparing the plate. The addition of rare earth elements in the magnesium alloy can effectively improve the flame retardant and corrosion resistant properties of the alloy, improve the plastic forming capability of the alloy and improve the mechanical properties of the alloy at room temperature and high temperature. Therefore, in recent years, the development and use of rare earth magnesium alloys have been receiving attention. The abundance of rare earth resources and magnesium resources in China makes China have certain advantages in the research aspect of Mg-RE series alloy. The rare earth element has high solid solubility in the magnesium alloy and has the characteristic of rapid reduction of the solid solubility along with the reduction of temperature, so that the Mg-RE alloy has good solid solution strengthening and age hardening effects. Therefore, the rare earth elements have the function of improving the performance of the magnesium alloy, which cannot be replaced by other elements. Recent researches find that the performance of the alloy can be effectively improved by performing plastic working on the rare earth alloy, including obtaining higher strength, when Wang et al performs hot rolling on Mg-12Gd-3Y-0.4Zr (wt.%) alloy at 450 ℃ and the cumulative deformation of 92%, a high-strength magnesium alloy plate with obviously refined grain size is obtained, the tensile strength of the high-strength magnesium alloy plate reaches 381.8MPa, and the yield strength of the high-strength magnesium alloy plate reaches 309.6 MPa. After the aging treatment is carried out at 225 ℃ for 17 hours, the tensile strength and the yield strength are further improved, the tensile strength reaches 456.8MPa, and the yield strength also reaches 348.9 MPa. However, the addition of a large amount of rare earth elements to magnesium alloys simultaneously causes a plurality of problems: (1) the excessive rare earth elements cause the density of the alloy to be higher, and the inherent advantage of light specific gravity of the magnesium alloy is weakened. (2) The rare earth magnesium alloy has poor elongation after aging treatment, and is not beneficial to the deep processing of the material in the later period. (3) The rare earth elements are expensive, and the magnesium alloy is added with a large amount of rare earth elements, so that the overall cost of the alloy is increased, and the large-scale mass production in the industry is not facilitated. Therefore, the magnesium alloy with low rare earth content is developed and designed, and the high strength of the material is realized by the aid of the thermomechanical treatment process, so that the magnesium alloy is more suitable for future industrial application of the magnesium alloy.

The invention relates to a low-cost high-strength rare earth magnesium alloy and a preparation technology thereof, and develops and designs a magnesium alloy Mg-Gd-Er-Zr alloy with low rare earth content, wherein the mass percent of the rare earth element Gd is less than or equal to 6 percent, the mass percent of Er is less than or equal to 2.0 percent, the total amount of rare earth is less than or equal to 8.0 percent, and the balance is Mg. In the invention, the magnesium alloy plate is prepared by regulating and controlling the rolling process parameters (rolling temperature, rolling reduction and heat preservation time), and the magnesium alloy plate has the characteristics of smooth surface, thin thickness, good formability and excellent mechanical property and has great potential in industrial application.

Disclosure of Invention

The invention aims at the problems that the prior high rare earth magnesium alloy has high production cost and low elongation after deformation processing. The invention discloses a magnesium alloy plate preparation technology which reduces the content of rare earth and has short industrial production flow. The invention has the characteristics that the rare earth content is effectively reduced and controlled to be below 8% (such as 7%) and the high strength of the plate is realized after the thermomechanical treatment. Firstly, after the cast alloy is subjected to solution treatment, the plate is rolled at different rolling temperatures by adopting a conventional rolling process, so that the high-strength high-toughness excellent mechanical property is obtained. The invention breaks through the defects of low strength and poor elongation of the current low rare earth magnesium metal, the form of the strengthening phase in the invention is represented by chain structure distribution of 5nm-20nm, the alloy realizes the aims of high strength and high toughness, the yield strength can reach 200-350 MPa, the tensile strength can reach 260-370 MPa, and the magnesium metal plate material has application prospect.

The magnesium alloy with lower rare earth content is designed for reducing the rare earth content in the magnesium alloy with rare earth and provides a preparation process thereof.

The invention relates to a rare earth magnesium alloy with low cost and high performance, which is characterized by comprising the following elements by mass: the mass percent of Gd which is a rare earth element is less than or equal to 6 percent, the mass percent of Er which is less than or equal to 2.0 percent, the total mass percent of rare earth is less than or equal to 8.0 percent, the mass percent of Zr which is less than or equal to 1.0 percent, the balance of Mg, and the mass percent of Gd and Er is not equal to 0.

The preparation process of the high-performance rare earth magnesium alloy comprises the following steps: carrying out heat treatment on the alloy casting blank, then rolling at different temperatures, wherein the rolling temperature interval is 300-450 ℃, the rolling speed is controlled at 8-12m/min, preferably 10m/min, the deformation of each pass is 8-10%, the time for returning and preserving heat between passes is 8-15min, and the accumulated deformation reaches 75% or more. Preferably, a cross rolling method is adopted, namely, the rolling direction of each pass is rotated by about 90 degrees compared with that of the previous pass. The final product, such as a plate with a thickness of 1.0 mm-1.5 mm, has smooth surface and edge and no cracking.

The grain size of the final product plate alloy is about 5-10 μm, a chain-shaped reinforcing phase different from the traditional reinforcing phase is generated, the width is 5nm-20nm, and the strength and the plasticity of the alloy can be improved at the same time. The alloy plate has the mechanical properties of yield strength of 200-350 MPa, tensile strength of 260-370 MPa and elongation of 2-10%.

The invention has the substantive characteristics and remarkable progress that:

(1) the invention discloses a magnesium metal material with low rare earth content, the total content of rare earth is less than or equal to 8.0 percent, and the content of rare earth is obviously lower than that of the common high-strength rare earth magnesium alloy material.

(2) The invention adopts a novel rolling technology, the total deformation can reach 75 percent or more in a rolling temperature range of 300-450 ℃, the rolling speed reaches 8-12m/min, the single-pass deformation is 8-10 percent, and the plate obtained by the rolling technology has smooth surface and good formability.

(3) The type of the strengthening phase in the invention is different from the type of the precipitated phase in the conventional Mg-Gd series alloy, and chain precipitation is generated in the alloy in the invention, which is helpful for improving the strength and the elongation of the material.

(4) The magnesium alloy plate with low rare earth content prepared by the method has excellent mechanical property, and is obviously higher than the magnesium alloy material with the same rare earth content.

(5) The alloy has simple preparation and processing methods and strong forming capability, and can obtain the magnesium metal plate with smooth surface and excellent mechanical property without special processing technology.

Drawings

FIG. 1 is a low-magnification TEM image of a chain-like reinforcing phase in example 1 of the present invention.

FIG. 2 is a high-magnification TEM image of a chain-like reinforcing phase in example 1 of the present invention.

Detailed Description

The present invention will be further illustrated with reference to the following examples, but the present invention is not limited to the following examples.

Example 1

Mg-6Gd-1Er-0.5Zr alloy obtained by common melting casting is subjected to solution treatment, then cutting and milling are carried out to obtain a rolled blank, and the blank is placed in a heat preservation furnace for treatment, wherein the temperature of the heat preservation furnace is 300 ℃. Setting the rolling speed to be 10m/min, setting the deformation of each pass to be 8%, rolling to rotate 90 degrees after one pass is finished, carrying out next pass of rolling, carrying out multi-pass rolling in such a way, keeping the temperature for 15min between each pass, and obtaining the plate with the thickness of 1.5mm by setting the rolling accumulated reduction to be 75%, and obtaining the mixed crystal structure with the grain size of 7.4 mu m, wherein Mg is a Mg-alloy mixed crystal structure with the grain size of 7.4 mu m₅The size of the (Gd, Er) strengthening phase is 240nm, the yield strength of the alloy is 349MPa, the tensile strength is 367MPa, and the elongation is 9.0%. The TEM of the chain-like strengthening phase in the alloy is shown in FIG. 1-2.

Example 2

Mg-5Gd-1Er-Zr alloy obtained by ordinary melt casting is subjected to solution treatment, andthen cutting, cutting and milling are carried out to obtain a rolled blank, and the blank is placed in a heat preservation furnace for processing, wherein the temperature of the heat preservation furnace is 350 ℃. Setting the rolling speed to be 10m/min, setting the deformation of each pass to be 10%, rolling to rotate 90 degrees after one pass is finished, carrying out next pass of rolling, carrying out multi-pass rolling in such a way, keeping the temperature for 8min between each pass, and obtaining the plate with the thickness of 1.5mm by setting the rolling accumulated reduction to be 75%, and obtaining the equiaxial crystal structure with the grain size of 4.3 mu m, wherein Mg is an Mg alloy with the grain size of 4.3 mu m₅The size of the (Gd, Er) strengthening phase is 270nm, the yield strength of the alloy is 310MPa, the tensile strength is 330MPa, and the elongation is 7.0%.

Example 3

Mg-4Gd-1Er-0.5Zr alloy obtained by common melting casting is subjected to solution treatment, then cutting and milling are carried out to obtain a rolled blank, and the blank is placed in a heat preservation furnace for treatment, wherein the temperature of the heat preservation furnace is 400 ℃. Setting the rolling speed to be 10m/min, setting the deformation of each pass to be 10%, rolling to rotate 90 degrees after one pass is finished, carrying out the next pass of rolling, carrying out the multiple passes of rolling in this way, keeping the temperature for 5min between each pass, and obtaining the plate with the thickness of 1.5mm by setting the rolling accumulated reduction to be 75%, and obtaining the equiaxial crystal structure with the grain size of 9.3 mu m, wherein the yield strength of the alloy is 230MPa, the tensile strength is 300MPa, and the elongation is 3%.

Example 4

Mg-1Gd-1Er-0.5Zr alloy obtained by common melting casting is subjected to solution treatment, then cutting and milling are carried out to obtain a rolled blank, and the blank is placed in a heat preservation furnace for treatment, wherein the temperature of the heat preservation furnace is 450 ℃. Setting the rolling speed to be 10m/min, setting the deformation of each pass to be 10%, rolling to rotate 90 degrees after one pass is finished, carrying out next pass of rolling, carrying out multi-pass rolling in such a way, keeping the temperature for 2min between each pass, and obtaining a plate with the thickness of 1.5mm by setting the rolling accumulated reduction to be 75%, obtaining an equiaxed crystal structure with the grain size of 10 microns, wherein the yield strength of the alloy is 200MPa, the tensile strength is 260MPa, and the elongation is 6.0%.

Examples 2-4 have TEM structure diagrams substantially similar to the examples.

Claims

1. The rare earth magnesium alloy with low cost and high performance is characterized by comprising the following elements by mass: the mass percent of Gd which is a rare earth element is less than or equal to 6 percent, the mass percent of Er which is less than or equal to 2.0 percent, the total mass percent of rare earth is less than or equal to 8.0 percent, the mass percent of Zr which is less than or equal to 1.0 percent, the balance of Mg, and the mass percent of Gd and Er is not equal to 0.

2. The process for preparing a high-performance rare earth magnesium alloy according to claim 1, comprising the steps of: carrying out heat treatment on the alloy casting blank, then rolling at different temperatures, wherein the rolling temperature interval is 300-450 ℃, the rolling speed is controlled at 8-12m/min, preferably 10m/min, the deformation of each pass is 8-10%, the time for returning and preserving heat between passes is 8-15min, and the accumulated deformation reaches 75% or more. Preferably, a cross rolling method is adopted, namely, the rolling direction of each pass is rotated by about 90 degrees compared with that of the previous pass.

3. The process for preparing a high-performance rare earth magnesium alloy according to claim 2, wherein the finally obtained product is a plate with the thickness of 1.0mm to 1.5mm, and the surface and the edge of the plate are smooth and have no cracks.

4. A process for preparing a high performance rare earth magnesium alloy as claimed in claim 3, wherein the grain size of the final product sheet alloy is about 5 to 10 μm.

5. The process for preparing a high-performance rare earth magnesium alloy according to claim 3, wherein a chain-like strengthening phase is generated, the width of which is 5nm to 20nm, and the strength and the plasticity of the alloy can be simultaneously improved.

6. The preparation process of the high-performance rare earth magnesium alloy according to claim 3, wherein the mechanical properties of the alloy plate are yield strength of 200-350 MPa, tensile strength of 260-370 MPa, and elongation of 2% -10%.