WO2021134947A1 - High-strength and high corrosion resistance magnesium alloy and preparation method therefor - Google Patents

Abstract

The present invention relates to a high-strength and high corrosion resistance magnesium alloy and a preparation method therefor. The high-strength and high corrosion resistance magnesium alloy comprises magnesium alloy AZ91D of a mass fraction of 98-98.5%, also comprises the following components, the percentage by mass of the components being as follows, Y: 0.75-1.0%; La: 0.26-0.35%; and Ce: 0.49-0.65%. The present invention, by adding mixed rare earth elements Y, La, and Ce into AZ91D magnesium alloy, utilizes the rare earth elements to refine magnesium grains and to strengthen the structure of the alloy, thus achieving the goal of increasing mechanical property of the AZ91D magnesium alloy and increasing corrosion resistance. The present invention has a simple process, inexpensive production costs, and provides great significance in terms of increasing the competitiveness of the magnesium alloy and of consuming and utilizing low-valued rare earth elements such as La, Ce, and Y.

Description

High-strength high-corrosion resistance magnesium alloy and preparation process thereof Technical field

The invention relates to the field of magnesium alloy forging, in particular to a high-strength and high-corrosion resistance magnesium alloy and a preparation process thereof.

Background technique

AZ91D magnesium alloy is currently the most widely used magnesium alloy, but due to its poor high-temperature strength and corrosion resistance, it can only be used in fields such as lampshades and communication product housings with lower requirements, and further applications in more demanding fields However, it is restricted, so on the basis of ensuring the original excellent performance of AZ91D magnesium alloy, the development of a magnesium alloy with higher mechanical properties and corrosion resistance has been chased by the market.

In order to achieve new purposes, some people have studied other methods to improve the mechanical properties and corrosion resistance of AZ91D magnesium alloys, but the methods used in the prior art have some limitations. "Mechanical properties method" (CN105525107A) introduces the purpose of improving the mechanical properties of magnesium alloys by adding promethium to AZ91D. But promethium is a radioactive element, which is very dangerous when used and operated.

In "A Method for Enhancing the Mechanical Properties of Magnesium Alloys" (CN2009101176062), Dai Jianfeng introduced that by adding carbon nanotubes to AZ91D to form composite materials, the purpose of improving the properties of magnesium alloys can be achieved. However, this method is complicated in process and costly in production. Higher.

Li Cong used high-value rare earth elements such as Gd, Nd, Er, etc. in "a rare earth magnesium alloy and its production process" (CN104328317B), and the added amount is still relatively high, which greatly increases this The use cost of this magnesium alloy is not conducive to promotion.

Therefore, in view of the shortcomings of the existing technology, a new technical solution needs to be designed.

Summary of the invention

The purpose of the present invention is to provide a magnesium alloy with high strength and high corrosion resistance by adding a variety of rare earth elements and a preparation process thereof.

In order to achieve the foregoing objective, the present invention provides a high-strength and high-corrosion-resistant magnesium alloy, comprising 98-98.5 wt% of magnesium alloy AZ91D, which is characterized in that it also includes the following components, and the mass percentage of each component is as follows:

Y: 0.75-1.0%;

La: 0.26-0.35%;

Ce: 0.49-0.65%.

As a further improvement of the present invention, the ratio of the content of Y to the sum of the content of La and Ce is Y/(La+Ce)=1.

As a further improvement of the present invention, the ratio of the content of La to the sum of the content of Y and Ce is La/(Y+Ce)=0.175.

As a further improvement of the present invention, the ratio of the content of Ce to the sum of the contents of Y and La is Ce/(Y+La)=0.325.

The invention also provides a process for preparing a magnesium alloy with high strength and high corrosion resistance, which includes the following steps:

a. Add 200kg of bottom flux to the 2.5T cast steel refining crucible that has been heated to pink. After the bottom flux is completely melted into a liquid, add 1600kg-1900kg of pure magnesium ingots into the crucible, and at the same time pass into the crucible with a purity greater than 99.99 % Nitrogen for stirring and blowing off the slag,

b. When the pure magnesium ingot is completely melted, heat the melt to 650°C-660°C, start the mixer, and add a flux consisting of 10kg-16kg refining agent, 6kg-10kg fluorite powder and 5kg-7kg manganese powder for the first step Refining, the refining time is 20 minutes,

c. After the first refining, increase the melt temperature to 670℃-690℃, add a flux composed of 8kg-10kg refining agent and 6kg-10kg fluorite powder for the second refining, and the refining time is 20-30 minutes , Adding 175-185kg pure aluminum ingot and 12-15kg pure zinc ingot at the same time,

d. Raise the temperature to 720℃ and carry out bottom slag extraction for 28-32 minutes. After the slag extraction, raise the melt temperature to 750℃-760℃, and add 40-46kg of La-Ce- with a rare earth content of 28-32%. The Y-Mg master alloy is put into the material basket, and the material basket is immersed in the metal liquid. At the same time, the rare earth special refining flux is added and the agitator is operated.

e. After the master alloy is completely melted, keep the melt temperature at 750℃-760℃ for 25-30 minutes, then lower the temperature to 720℃-740℃, carry out the second bottom slag extraction, after the bottom slag extraction, cool down , Stand still until the temperature drops to 660°C-670°C, then transfer the melt to a holding furnace for casting, and finally obtain the high-strength and high-corrosion resistance magnesium alloy.

As a further improvement of the present invention, after the end of step c, sample the furnace for spectral analysis of components, if the weight percentage of each component meets the following conditions: Al: 8.80-9.20%, Mn: 0.20-0.4%, Zn: 0.60 %-0.80%, Re: 1.50%-2.50%, Fe: ≤0.04%, Cu: ≤0.025%, Ni: ≤0.0001%, Si: ≤0.05%, proceed to step d, if not satisfied, follow the results of spectral analysis Adjust the corresponding element composition until the above conditions are met.

As a further improvement of the present invention, the calculation formula for the added amount of the element that does not meet the results of the spectral analysis is the weight of the molten metal in the crucible* (the target value of the metal element content-the actual measured value of the metal element).

The beneficial effects of the present invention:

In the present invention, the mixed rare earth elements Y, La and Ce are added to the AZ91D magnesium alloy, the magnesium crystal grains are refined by the rare earth elements, and the alloy structure is strengthened, thereby achieving the purpose of improving the mechanical properties of the AZ91D magnesium alloy and improving the corrosion resistance. The invention has simple process and low production cost, and is of great significance for increasing the competitiveness of magnesium alloys and digesting and utilizing low-value rare earth elements of La, Ce, and Y.

Detailed ways

The present invention will be described in detail below in conjunction with the specific embodiments shown in the drawings.

The magnesium alloy AZ91D involved in this embodiment is an alloy product with a wide range of uses in the international market. The standard content is as follows:

name	Mg	Al	Zn	Mn	Si	Cu	Ni	Fe
AZ91D	margin	8.5-9.5	0.45-0.90	0.17-0.4	<=0.05	<=0.025	<=0.001	<=0.004

The basic performance parameters are as follows:

The invention embodies the purpose of the invention through specific embodiments.

Example 1

This embodiment provides a process for preparing a magnesium alloy with high strength and high corrosion resistance, and the specific steps are as follows:

Add 200kg of bottom flux to the 2.5T cast steel refining crucible that has been heated to pink. After the bottom flux is completely melted into a liquid, add 1800kg of pure magnesium ingots into the crucible, and at the same time pass 99.99% nitrogen into the crucible for stirring and Blow off slag

When the pure magnesium ingot is completely melted, raise the melt to 660°C in the greenhouse, turn on the mixer, and slowly add a flux consisting of 12kg refining agent, 8kg fluorite powder and 6kg manganese powder for the first refining, and the refining time is 20 minutes;

After the first refining, increase the melt temperature to 680℃, add a flux composed of 10kg refining agent and 8kg fluorite powder for the second refining, refining time is 20 minutes, and add 180kg pure aluminum ingot and 13kg pure zinc at the same time ingot;

After the secondary refining is completed, samples are taken for spectral analysis of the composition. If it is qualified, proceed to the next process, if it is unqualified, add alloying elements.

Raise the temperature to 720℃, carry out bottom slag extraction for 30 minutes, after the slag extraction, raise the melt temperature to 760℃, add 42kg of La-Ce-Y-Mg master alloy with 30% rare earth content to the basket, and Immerse the basket in the metal liquid, add the rare earth special refining flux and run the agitator at the same time;

After the master alloy is completely melted, keep the melt temperature at 760℃ for 30 minutes, then lower the temperature to 740℃, carry out the second bottom slag lifting, after the bottom slag is lifted, cool and stand until the temperature drops to 660 ℃, the melt is transferred to a holding furnace for casting, and finally an AZ91D magnesium alloy ingot containing 0.5% rare earth is obtained. Take the magnesium alloy for high temperature strength, salt spray test and metallographic inspection.

In the above-mentioned Examples 1 and 2, after the second refining, the furnace was sampled for spectral analysis of components. If the weight percentage of each component satisfies the following conditions: Al: 8.80-9.20%, Mn: 0.20-0.4%, Zn :0.60%-0.80%, Re: 1.50%-2.50%, Fe: ≤0.04%, Cu: ≤0.025%, Ni: ≤0.0001%, Si: ≤0.05%, proceed to step d, if not satisfied, according to the spectrum The analysis results are adjusted to the corresponding element composition until the above conditions are met.

The calculation formula for the added amount of the detected elements that do not meet the results of the spectral analysis is:

Weight of molten metal in the crucible* (target value of metal element content-actual measured value of metal element).

Example 2

The preparation process of this embodiment is carried out according to the steps of Example 1, the difference is that the 30% La-Ce-Y-Mg master alloy is added to 83kg, and finally an AZ91D magnesium alloy ingot containing 1.0% rare earth is obtained. The magnesium alloy undergoes high-temperature strength, salt spray test and metallographic testing.

Example 3

The preparation process of this embodiment is carried out according to the steps of Example 1. The difference is that the 30% La-Ce-Y-Mg master alloy is added to 125kg, and finally an AZ91D magnesium alloy ingot containing 1.5% rare earth is obtained. The magnesium alloy undergoes high-temperature strength, salt spray test and metallographic testing.

Example 4

The preparation process of this embodiment is carried out according to the steps of Example 1, the difference is that the 30% La-Ce-Y-Mg master alloy is added to 167kg, and finally an AZ91D magnesium alloy ingot containing 2.0% rare earth is obtained. The magnesium alloy undergoes high-temperature strength, salt spray test and metallographic testing.

Example 5

The preparation process of this embodiment is carried out according to the steps of Example 1, the difference is that the 30% La-Ce-Y-Mg master alloy is added to 209kg, and finally an AZ91D magnesium alloy ingot containing 2.5% rare earth is obtained. The magnesium alloy undergoes high-temperature strength, salt spray test and metallographic testing.

In order to illustrate the advantages of the present invention, another set of control samples were added. The samples were not added to the rare earth element formula of the present invention. The magnesium alloy was used for high-temperature strength, salt spray test and metallographic testing. The results are shown in Table 1 and Figure 6. Show.

The high temperature strength test results of the magnesium alloy samples in the above embodiment and the comparative example are shown in Table 1.

Table 1

test results	Control sample	Example 1	Example 2	Example 3	Example 4	Example 5
High temperature tensile strength MPa	155	188	191	199	187	185
High temperature tensile strength increase percentage%	/	21.29	23.23	28.39	20.65	19.35
High temperature elongation	3.10	4.50	4.80	5.67	5.46	5.06
High temperature elongation increase percentage%	/	45.16	54.83	82.90	76.12	63.22

It can be seen from the data in Table 1 that the high temperature strength and elongation of magnesium alloy AZ91D after adding La, Ce, and Y rare earth elements have been significantly improved. When the addition amount is 1.5%, the increase is the largest.

The metallographic diagrams of the magnesium alloy samples in the above embodiment and the comparative example after the metallographic detection are shown in Figure 1-6, in which Figure 1 is the metallographic diagram of the control sample, and Figures 2-6 correspond to the metallographic diagram of Example 1-5 . It can be seen from the comparison of Figures 1-6 that after adding La, Ce, and Y rare earth elements to the magnesium alloy AZ91D, its grains have been significantly refined and the alloy structure has been strengthened.

The top views obtained after the salt spray test of the magnesium alloy samples in the above embodiment and the comparative example are shown in Figs. 7 and 8, wherein Fig. 7 is the result after 24h, and Fig. 8 is the result after 48h. Figures 7 and 8 correspond to the results of the control sample and Examples 1-5 after the salt spray test from left to right. From the comparison of Figure 7 and Figure 8, it can be seen that the corrosion resistance of magnesium alloy AZ91D after the addition of La, Ce, and Y rare earth elements is significantly improved. The effect is most obvious when the addition amount is 1.5%, and when the addition amount is higher than 2 %Time.

It should be understood that although this specification is described in accordance with the implementation manners, not each implementation manner only includes an independent technical solution. This narration in the specification is only for the sake of clarity, and those skilled in the art should regard the specification as a whole. The technical solutions in the embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

The series of detailed descriptions listed above are only specific descriptions of feasible implementations of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent implementations or implementations made without departing from the technical spirit of the present invention All changes shall be included in the protection scope of the present invention.

Claims (7)

1. A high-strength and high-corrosion resistance magnesium alloy, comprising 98-98.5% mass fraction of magnesium alloy AZ91D, characterized in that it also includes the following components, and the mass percentages of each component are as follows:

   Y: 0.75-1.0%;

   La: 0.26-0.35%;

   Ce: 0.49-0.65%.
2. The high-strength and high-corrosion resistance magnesium alloy according to claim 1, wherein the ratio of the content of Y to the sum of the content of La and Ce is Y/(La+Ce)=1.
3. The high-strength and high-corrosion resistance magnesium alloy according to claim 1, wherein the ratio of the content of La to the sum of the content of Y and Ce is La/(Y+Ce)=0.175.
4. The high-strength and high-corrosion resistance magnesium alloy according to claim 1, wherein the ratio of the content of Ce to the sum of the contents of Y and La is Ce/(Y+La)=0.325.
5. A preparation process of high-strength and high-corrosion resistance magnesium alloy, which is characterized in that it comprises the following steps: a. Add 200kg of bottom flux to the 2.5T cast steel refining crucible heated to pink, and wait until the bottom flux is completely melted into a liquid. , Add 1600kg-1900kg pure magnesium ingot into the crucible, and at the same time pass nitrogen with purity greater than 99.99% into the crucible to stir and blow off the slag.

   b. When the pure magnesium ingot is completely melted, heat the melt to 650°C-660°C, start the mixer, and add a flux consisting of 10kg-16kg refining agent, 6kg-10kg fluorite powder and 5kg-7kg manganese powder for the first step Refining, the refining time is 20 minutes,

   c. After the first refining, increase the melt temperature to 670℃-690℃, add a flux consisting of 8kg-10kg refining agent and 6kg-10kg fluorite powder for the second refining, and the refining time is 20-30 minutes , Add 175-185kg pure aluminum ingot and 12-15kg pure zinc ingot at the same time,

   d. Raise the temperature to 720℃ and carry out bottom slag extraction for 28-32 minutes. After the slag extraction, raise the melt temperature to 750℃-760℃, and add 40-46kg of La-Ce- with a rare earth content of 28-32%. The Y-Mg master alloy is put into the material basket, and the material basket is immersed in the metal liquid. At the same time, add the rare earth special refining flux and run the agitator.

   e. After the master alloy is completely melted, keep the melt temperature at 750℃-760℃ for 25-30 minutes, then lower the temperature to 720℃-740℃, carry out the second bottom slag extraction, after the bottom slag extraction, cool down , Stand still until the temperature drops to 660°C-670°C, then transfer the melt to a holding furnace for casting, and finally obtain the high-strength and high-corrosion resistance magnesium alloy.
6. The preparation process of the high-strength and high-corrosion resistance magnesium alloy according to claim 5, characterized in that: after the step c is completed, a sample is taken in the furnace for spectral analysis of components, if the weight percentage of each component meets the following conditions: Al: 8.80-9.20%, Mn:0.20-0.4%, Zn:0.60%-0.80%, Re:1.50%-2.50%, Fe:≤0.04%, Cu:≤0.025%, Ni:≤0.0001%, Si:≤0.05 %, then proceed to step d, if not satisfied, adjust the corresponding element composition according to the results of the spectral analysis until the above conditions are met.
7. The preparation process of a magnesium alloy with strong and high corrosion resistance according to claim 6, wherein the calculation formula for the added amount of the element that does not meet the results of the spectral analysis is:

   Weight of molten metal in the crucible* (target value of metal element content-actual measured value of metal element).

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