CN110656270B

CN110656270B - Die-casting magnesium alloy and preparation method and application thereof

Info

Publication number: CN110656270B
Application number: CN201810699719.7A
Authority: CN
Inventors: 巩泉雨; 曹梦梦; 郭强
Original assignee: BYD Co Ltd
Current assignee: BYD Co Ltd
Priority date: 2018-06-29
Filing date: 2018-06-29
Publication date: 2021-11-12
Anticipated expiration: 2038-06-29
Also published as: CN110656270A

Abstract

The invention relates to the field of die-casting magnesium alloys, and discloses a die-casting magnesium alloy and a preparation method and application thereof. Based on the total weight of the magnesium alloy, the magnesium alloy comprises the following components: 2-6 wt% of Al, 2-4.5 wt% of Y, 1.5-3 wt% of Zn, 0.1-1.5 wt% of Ca, 0.05-0.3 wt% of Mn, 0.05-0.1 wt% of La, 0.05-0.1 wt% of Ce, 0.005-0.01 wt% of Nd, 84.39-94.145 wt% of Mg and less than 0.1 wt% of impurities. The magnesium alloy has good mechanical property, heat-conducting property and flow formability, and can still have good mechanical property after being recycled for many times.

Description

Die-casting magnesium alloy and preparation method and application thereof

Technical Field

The invention relates to the field of die-casting magnesium alloys, in particular to a die-casting magnesium alloy and a preparation method and application thereof.

Background

Die casting is one of basic forming methods of magnesium alloy, and can be used for product design of complex structural parts. The commonly used magnesium alloy die-casting material is AZ91D, the material has good flow forming performance, large forming process window and high cost performance, and the material is widely used for magnesium alloy die-casting products.

The main component elements of the AZ91D material are 8.5-9.5 wt% of aluminum, 0.45-0.9 wt% of zinc, 0.17-0.4 wt% of manganese, less than or equal to 0.05 wt% of silicon, less than or equal to 0.025 wt% of copper, less than or equal to 0.001 wt% of nickel, and less than or equal to 0.004 wt% of iron. The AZ91D material has the characteristics of high specific strength and greatly improved corrosion resistance compared with pure magnesium. The bracket is mainly used for shells of electric products, small-size thin or special-shaped brackets and the like. However, the mechanical properties of the product body after the AZ91D material is die-cast are general, the tensile strength is 210-220MPa, the yield strength is 150-160MPa, the hardness is about 75HV, and the impact toughness is about 15kJ/m²And the magnesium alloy die casting product with higher requirement on bearing force cannot be met.

CN1965099A discloses a high strength and toughness magnesium-based alloy, which comprises 1-8% rare earth elements and 1-6% calcium by weight, and the maximum crystal grain diameter of magnesium forming the matrix is below 30 μm. Further, at least one kind of element selected from the group consisting of 0.5 to 6% of zinc, 2 to 15% of aluminum, 0.5 to 4% of manganese, 1 to 8% of silicon, and 0.5 to 2% of silver on a weight basis is contained. The tensile strength (sigma) is 350MPa or more, and the elongation at break (epsilon) is 5% or more. The product of the tensile strength (sigma) and the elongation at break (epsilon) is sigma x epsilon is more than or equal to 4000 MPa. The rare earth element includes at least one element selected from the group consisting of cerium (Ce), lanthanum (La), yttrium (Y), ytterbium (Yb), gadolinium (Gd), terbium (Tb), scandium (Sc), samarium (Sm), praseodymium (Pr), and neodymium (Nd). Contains 1.5-4% of manganese, 2-15% of aluminum and less than 10ppm of iron by weight, and the maximum grain diameter of the Al-Mn compound is less than 20 μm. Can be excellent in tensile strength, elongation at break and fatigue strength at ordinary temperature and has high heat-resistant strength characteristics at around 200 ℃, and is useful for automobile parts, particularly engine parts and transmission parts used at high temperatures. Due to the addition of Ag and a large amount of rare earth elements, the material cost is too high, and the method is not suitable for large-scale industrial production.

CN105385917A discloses a high-strength high-plasticity magnesium alloy, which comprises the following chemical components in percentage by mass: 7.5 to 9.0 percent of Al7, 0.5 to 1.0 percent of Zn0, 0.1 to 0.5 percent of Mn0, 0.1 to 1.0 percent of La0, 0.1 to 1.0 percent of Y, 0.1 to 1.0 percent of Nd0, 0.1 to 1.0 percent of Ca0, and the balance of Mg and inevitable impurity elements. The method is used for overcoming the defects of low strength, poor plasticity and the like of the die-casting magnesium alloy. In the casting state, the tensile strength of the magnesium alloy is 268-301MPa, the yield strength is 175-195MPa, and the elongation is 5.2-10.2%. The alloy has excessive aluminum elements, no effective elements are used for reducing the solid solution strengthening of Al, the heat conducting property of the material is poor, and the optimal strength and heat conducting property cannot be realized.

CN102803533A discloses a magnesium alloy sheet containing Al and Mn, wherein when a region from the surface of the alloy sheet to 30% of the thickness of the alloy sheet in the thickness direction of the magnesium alloy sheet is defined as a surface region and 50 μm is arbitrarily selected from this surface region²In the sub-region (b), the number of particles as a crystal phase containing both Al and Mn and having a maximum diameter of 0.1 to 1 μm is 15 or less, and the mass ratio of Al to Mn in the particles of the crystal phase, Al/Mn, is 2 to 5. Further, the magnesium alloy contains 5 to 12 mass% of Al and 0.1 to 2.0 mass% of Mn. Further contains Zn, Si, Ca, Sr, Y, Cu, Ag, Ce, Zr and rare earthAt least one element of elements (other than Y and Ce). The magnesium alloy is used for providing a magnesium alloy with high impact resistance even in a low-temperature environment, but the magnesium alloy has obvious solid solution strengthening, greatly reduces the heat-conducting performance of the material, and cannot be used as a heat-conducting structural member.

CN1434143A discloses a die-cast magnesium alloy having excellent heat resistance and castability, which contains 1.5 to 6% by weight of aluminum, 0.3 to 2% by weight of calcium, 0.01 to 1% by weight of strontium, 0.1 to 1% by weight of manganese, and the balance of magnesium and inevitable impurities. Also contains 0.001-1 wt% of silicon, 0.2-1 wt% of zinc, 0.1-3 wt% of rare earth elements. In order to have excellent heat resistance and castability and excellent creep properties. Strontium has heat resistance, but more than 0.5% results in a decrease in corrosion properties and a decrease in heat conductivity.

However, there is a need in the industry for a die-cast magnesium alloy that has good mechanical properties, thermal conductivity, and molding fluidity, and can maintain good mechanical properties after being recycled for many times.

Disclosure of Invention

The invention aims to provide a die-casting magnesium alloy with the performance, a die-casting magnesium alloy and a preparation method and application thereof.

In order to achieve the above object, a first aspect of the present invention provides a die-cast magnesium alloy comprising, based on the total weight of the magnesium alloy: 2-6 wt% of Al, 2-4.5 wt% of Y, 1.5-3 wt% of Zn, 0.1-1.5 wt% of Ca, 0.05-0.3 wt% of Mn, 0.05-0.1 wt% of La, 0.05-0.1 wt% of Ce, 0.005-0.01 wt% of Nd, 84.39-94.145 wt% of Mg and less than 0.1 wt% of impurities.

Preferably, the weight ratio of Y to Zn is 1-2: 1.

preferably, the weight ratio of La, Ce and Nd is (9-10): (9-10): 1.

Preferably, the total content of La, Ce and Nd in the magnesium alloy is 0.1-0.3 wt%.

Preferably, the yield strength of the magnesium alloy is 185-220 MPa; the tensile strength is 270-300 MPa; the elongation is 6-8%; the thermal conductivity is 80-90W/(m.K).

A second aspect of the present invention provides a method for producing the die-cast magnesium alloy of the present invention, comprising: (1) smelting raw materials containing Al, Y, Zn, Ca, Mn, La, Ce, Nd and Mg elements to obtain alloy liquid; (2) and casting the alloy liquid, and cooling to obtain the magnesium alloy.

Preferably, the smelting in step (1) comprises performing at 700-750 ℃ for 20-60 min.

Preferably, a protective agent is also added in the step (1) to protect the melt; the protective agent comprises a covering agent, a mixed gas of nitrogen and sulfur hexafluoride or an inert gas; the addition amount of the covering agent is 1-5 wt% of the raw material, and the covering agent comprises MgCl₂KCl, NaCl and CaF₂At least one of (1).

Preferably, step (1) also comprises argon blowing and stirring during the smelting process.

Preferably, the method further comprises the steps of carrying out aging treatment on the magnesium alloy, and then naturally cooling; preferably, the aging treatment temperature is 120-220 ℃, and the aging treatment time is more than 0.5 h.

A third aspect of the invention provides the use of the die-cast magnesium alloy of the invention in a high-strength heat-conducting structural material.

Through the technical scheme, the magnesium alloy containing multiple element components can improve the performance of the magnesium alloy, provides the die-casting magnesium alloy with good mechanical property, heat-conducting property and flow formability, and can still have good mechanical property after being recycled for many times.

Detailed Description

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

In a first aspect of the present invention, there is provided a die-cast magnesium alloy comprising, based on the total weight of the magnesium alloy: 2-6 wt% of Al, 2-4.5 wt% of Y, 1.5-3 wt% of Zn, 0.1-1.5 wt% of Ca, 0.05-0.3 wt% of Mn, 0.05-0.1 wt% of La, 0.05-0.1 wt% of Ce, 0.005-0.01 wt% of Nd, 84.39-94.145 wt% of Mg and less than 0.1 wt% of impurities.

The die-casting magnesium alloy provided by the invention has good mechanical property, heat conductivity and flow formability, and can still have good mechanical property after being recycled for multiple times. Preferably, the magnesium alloy comprises: 3-5 wt% of Al, 2-3.5 wt% of Y, 2.3-3 wt% of Zn, 0.5-1.5 wt% of Ca, 0.1-0.2 wt% of Mn, 0.07-0.09 wt% of La, 0.07-0.09 wt% of Ce, 0.008-0.009 wt% of Nd, 86.511-91.852 wt% of Mg and less than 0.1 wt% of impurities.

According to the present invention, the die-cast magnesium alloy containing Al in the above-mentioned content range can contribute to the magnesium alloy having both improved castability and mechanical properties. When the content of Al is more or less than the above content range, the simultaneous improvement of mechanical, thermal conductivity and flow formability cannot be provided.

According to the present invention, the mechanical properties of the die-cast magnesium alloy can be improved by including Y and Zn in the die-cast magnesium alloy in the above-mentioned content ranges. Preferably, Y and Zn are used together, so that the magnesium alloy has better effects of improving the tensile strength, the extensibility and the impact toughness. Preferably, the weight ratio of Y to Zn is 1-2: 1; more preferably, the weight ratio of Y to Zn is 1.5: 1.

according to the present invention, the die-cast magnesium alloy containing Mn in the above-mentioned content range can contribute to improvement of ductility and impact toughness of the magnesium alloy. In addition, the content of Mn in the range can also have favorable influence on the heat-conducting property and the corrosion resistance of the magnesium alloy. When the content of Mn is higher or lower than the above content range limit, the heat conductive property and/or the corrosion resistance of the die-cast magnesium alloy may be deteriorated.

According to the present invention, the die-cast polymetallic alloy contains Ca in the above-mentioned content range, and can contribute to improvement of the thermal conductivity of the magnesium alloy. When the content of Ca is more or less than the above content range limit, the heat conductive property of the die-cast magnesium alloy becomes poor.

According to the invention, the die-cast magnesium alloy contains a plurality of rare earth elements, La, Ce and Nd. Their limited content may contribute to the improvement of the heat conductive property and toughness of the magnesium alloy. Considering the balance of various properties to be achieved by the die-cast magnesium alloy, it is preferable that the total content of La, Ce, and Nd in the magnesium alloy is 0.1 to 0.3 wt%. Further, the definition between the plurality of rare earth elements contained in the magnesium alloy may lead to better performance of the magnesium alloy. Preferably, the weight ratio of La, Ce and Nd is (9-10):1, more preferably, the weight ratio of La, Ce and Nd is 10:10: 1.

In the present invention, the die-cast magnesium alloy inevitably contains impurities such as less than 0.05 wt% of Fe, less than 0.05 wt% of Cu, or other elements, but less than 0.01 wt%. The total content of the impurities is less than 0.1 weight percent.

The die-casting magnesium alloy provided by the invention has multiple components with the contents, and has better mechanical property, heat conduction property and flow formability when the Y and Zn, and the La, Ce and Nd meet the defined relationship, and the alloy can still have better mechanical property after being recycled for multiple times.

According to the invention, the yield strength of the die-cast magnesium alloy is preferably 185-220 MPa; the tensile strength is 270-300 MPa; the elongation is 6-8%; the thermal conductivity is 80-90W/(m.K).

In the invention, more preferably, the step (1) is carried out in an oxygen-free environment, and the quality of the magnesium alloy obtained by the method is better.

In the present invention, the raw material containing the above-mentioned element may be an intermediate alloy or a simple metal. As long as the composition of the die-cast magnesium alloy of the present invention can satisfy the melting in step (1).

According to the present invention, preferably, the smelting in step (1) comprises performing at 700-750 ℃ for 20-60 min.

According to the invention, preferably, a protective agent is also added in step (1) to protect the melt; the protective agent comprises a covering agent, a mixed gas of nitrogen and sulfur hexafluoride or an inert gas; the addition amount of the covering agent is 1-5 wt% of the raw material, and the covering agent comprises MgCl₂KCl, NaCl and CaF₂At least one of (1). Preferably, the covering agent is added in any combination of numerical ranges between 1 wt%, 2 wt%, 3 wt%, 4 wt% and 5 wt% of the raw material.

According to the invention, preferably, step (1) also comprises argon blowing stirring during the smelting process. The argon gas may be high purity argon gas having a purity of 99.99% or more.

According to the invention, preferably, the method further comprises the steps of carrying out aging treatment on the magnesium alloy, and then naturally cooling; preferably, the aging treatment temperature is 120-220 ℃, and the aging treatment time is more than 0.5 h.

The present invention will be described in detail below by way of examples.

Example 1

Alloy raw materials containing various elements were prepared in accordance with the magnesium alloy compositions shown in table 1.

Smelting the alloy raw materials in a smelting furnace, and adding MgCl with the weight percent of 3% of the alloy raw materials₂Blowing 99.99 percent of high-purity argon gas into the mixture during the smelting process, stirring the mixture, and smelting the mixture for 30min at the temperature of 720 ℃.

And injecting the melt into a metal mold, and cooling to obtain the magnesium alloy casting.

And (3) carrying out aging treatment on the prepared magnesium alloy casting at 150 ℃ for 5 h. And after the aging treatment is finished, naturally cooling to room temperature. Obtaining the die-casting magnesium alloy YM-1.

Example 2

The alloy raw materials are put into a smelting furnace for smelting, mixed gas of nitrogen and sulfur hexafluoride is added, 99.99% of high-purity argon is blown in during the smelting process, the mixture is stirred, and the alloy is smelted for 20min at 750 ℃.

And (3) carrying out aging treatment on the prepared magnesium alloy casting at 120 ℃ for 24 h. And after the aging treatment is finished, naturally cooling to room temperature. Obtaining the die-casting magnesium alloy YM-2.

Example 3

The process of example 1 was followed except that the prepared magnesium alloy casting was subjected to aging treatment at 300 ℃ for 2 hours. And after the aging treatment is finished, naturally cooling to room temperature. Obtaining the die-casting magnesium alloy YM-3.

Example 4

The alloy raw materials are put into a smelting furnace for smelting, NaCl with the weight percent of 2 percent of the alloy raw materials is added, 99.99 percent of high-purity argon is blown in during the smelting process, the mixture is stirred, and the smelting is carried out for 60min at the temperature of 700 ℃.

And injecting the melt into a metal mold, and cooling to obtain the magnesium alloy casting YM-4.

Example 5

The procedure of example 1 was followed except that the contents of Y and Zn were 3% and 3%, respectively.

Obtaining the die-casting magnesium alloy YM-5.

Example 6

The procedure of example 1 was followed except that the contents of Y and Zn were 2% and 3%, respectively.

Obtaining the die-casting magnesium alloy YM-6.

Example 7

The procedure of example 1 was followed except that the total content of La, Ce and Nd was 0.096% by weight, and the content of La, Ce and Nd was 0.008%, 0.008% and 0.08%, respectively.

Obtaining the die-casting magnesium alloy YM-7.

Example 8

The procedure of example 1 was followed except that the total content of La, Ce and Nd was 0.169% by weight (0.08%, 0.08% and 0.009%).

Obtaining the die-casting magnesium alloy YM-8.

Example 9

The die-casting magnesium alloy YM-1 obtained in example 1 was remelted and returned, and die-cast magnesium alloy YM-9 was obtained in the same manner as in example 1.

EXAMPLE 10

A die-cast magnesium alloy YM-10 was prepared in the same manner as in example 1.

Example 11

A die-cast magnesium alloy YM-11 was prepared in the same manner as in example 1.

Comparative example 1

The procedure of example 1 was followed except that Y was replaced with equal amounts by weight of La, Ce and Nd.

Obtaining the die-casting magnesium alloy D-1.

Comparative example 2

The procedure of example 1 was followed except that Zn was replaced with Al of equal mass.

Obtaining the die-casting magnesium alloy D-2.

Comparative example 3

The procedure is as in example 1, except that Ca is Al in equal weight.

Obtaining the die-casting magnesium alloy D-3.

Comparative example 4

The procedure of example 1 was followed except that La, Ce, Nd were replaced with Al of equal mass. Obtaining the die-casting magnesium alloy D-4.

Comparative example 5

The procedure of example 1 was followed except that Mn was replaced with Al of equal weight.

Obtaining the die-casting magnesium alloy D-5.

Comparative example 6

The procedure is as in example 1, except that the amount of Y is 1%.

Obtaining the die-casting magnesium alloy D-6.

TABLE 1

Test example

The die-cast magnesium alloys YM-1 to YM-11, D-1 to D-6 were subjected to the following property measurements, and the results are shown in Table 2.

Tensile strength: the tensile test method was carried out by means of a universal tester in accordance with GB/T228.1-2010.

Impact toughness: measured according to the GB/T229-2007 impact test method.

Formability: the evaluation standard is die-casting mosquito incense molds, and the flowability is judged according to the length of the die-casting mosquito incense molds. And (3) comparing the lengths of the die-casting mosquito-repellent incense dies by using AZ91D as a standard part under the same die-casting parameters. When the length of the sample die-casting mosquito-repellent incense die is more than or equal to that of the AZ91D die-casting mosquito-repellent incense die, the formability is recorded as excellent; when the length of the sample die-casting mosquito-repellent incense die is less than or equal to 80% of the length of the AZ91D die-casting mosquito-repellent incense die, the formability is recorded as poor; when the length of the AZ91D die-casting mosquito-repellent incense die is more than 80% and the length of the sample die-casting mosquito-repellent incense die is less than the length of the AZ91D die-casting mosquito-repellent incense die, the formability is good.

Hardness test: according to GB/T231.1-2009, a magnesium alloy wafer with the diameter of 12.7mm and the thickness of 3mm is tested for more than 3 times under the conditions that the pressing force is 3kg and the dwell time is 15s by adopting a Vickers hardness tester, and the average value of the obtained data is the measured hardness of the magnesium alloy, and the unit is HV.

Test of thermal conductivity: a magnesium alloy wafer 12.7mm in diameter and 3mm in thickness was subjected to a test of thermal conductivity by a laser flash method according to the test method of ASTM E1461-07.

Tensile property test: according to the test method of ISO 6892-1, the smelted magnesium alloy melt is die-cast into a die cavity by using semi-solid casting equipment to obtain a tensile casting with the wall thickness of 1.5mm, and a universal mechanical testing machine is used for tensile test to obtain the yield strength and the elongation percentage, wherein the yield strength is the yield limit generating 0.2% of residual deformation, and the elongation percentage is the elongation at break.

And (3) corrosion resistance testing: the magnesium alloy obtained was cast into a sheet of 100mm × 100mm × 1.5mm, and immersed in a 3.5 wt% NaCl aqueous solution for 48 hours (i.e., 2 days), and the corrosion rate was calculated by the weight loss method as follows:

V＝(m₁-m₂)/(t×s)

wherein m is₁The mass of the magnesium alloy sample before soaking is measured in mg;

m₂the mass of the magnesium alloy sample is measured in mg after the magnesium alloy sample is soaked, cleaned by distilled water and dried to constant weight at 120 ℃;

t is the soaking time in days;

s is the surface area of the magnesium alloy sample in cm²Counting;

v is the corrosion rate in mg/(cm)²D) meter.

The die-casting magnesium alloy can still have mechanical properties after being repeatedly utilized.

TABLE 2

The results of the examples and the comparative examples in tables 1 and 2 show that the examples adopting the technical scheme provided by the invention can provide the die-cast magnesium alloy with good mechanical property, thermal conductivity and flow formability. As in example 9, the alloy can still have good mechanical properties after being recycled for many times.

The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims

1. A die-cast magnesium alloy comprising, based on the total weight of the magnesium alloy:

3-5% by weight of Al,

2-3.5% by weight of Y,

2.3-3 wt.% of Zn,

0.5 to 1.5% by weight of Ca,

0.1 to 0.2 wt.% of Mn,

0.07-0.09 wt% of La,

0.07-0.09 wt.% of Ce,

0.008-0.009 wt% of Nd,

86.511-91.852 wt.% Mg and 0.1 wt.% or less impurities;

wherein, the weight ratio of La, Ce and Nd is (9-10): (9-10):1, and the thermal conductivity of the magnesium alloy is 80-90W/(m.K).

2. The magnesium alloy of claim 1, wherein the weight ratio of Y to Zn is 1-2: 1.

3. the magnesium alloy according to claim 1, wherein the total content of La, Ce and Nd is 0.1-0.3 wt%.

4. The magnesium alloy of claim 1, wherein the magnesium alloy has a yield strength of 185-220 MPa; the tensile strength is 270-300 MPa; the elongation is 6-8%.

5. A method for producing the die-cast magnesium alloy as claimed in any one of claims 1 to 4, comprising:

(1) smelting raw materials containing Al, Y, Zn, Ca, Mn, La, Ce, Nd and Mg elements to obtain alloy liquid;

(2) and casting the alloy liquid, and cooling to obtain the magnesium alloy.

6. The method as claimed in claim 5, wherein the smelting in step (1) comprises performing at 700-750 ℃ for 20-60 min.

7. The method according to claim 5 or 6, wherein a protective agent is further added in step (1) to protect the melt; the protective agent comprises a covering agent, a mixed gas of nitrogen and sulfur hexafluoride or an inert gas; the addition amount of the covering agent is 1-5 wt% of the raw material, and the covering agent comprises MgCl₂KCl, NaCl and CaF₂At least one of (1).

8. The method of claim 5 or 6, further comprising aging the magnesium alloy followed by natural cooling; the aging treatment temperature is 120-220 ℃, and the aging treatment time is more than 0.5 h.

9. The method of claim 7, further comprising aging the magnesium alloy followed by natural cooling; the aging treatment temperature is 120-220 ℃, and the aging treatment time is more than 0.5 h.

10. Use of a die-cast magnesium alloy according to any of claims 1 to 4 in a high strength heat conducting structural material.