EA014150B1 - Process for casting a magnesium alloy - Google Patents

Abstract

A process for casting a magnesium alloy consisting of 5 - 1300 % by weight of aluminium, 0.00 - 22.00 % by weight of zinc, also containing 0.10 - 0.5 % by weight of manganese, and the balance being magnesium and unavoidable impurities, the total impurity level being below 0.1 % by weight, wherein the alloy is cast in a die in which the temperature is controlled in the range of 150-340°C, the die is filled in a time which expressed in milliseconds is equal to the product of a number between 2 and 300 multiplied by the average part thickness expressed in millimeter, the static metal pressures being maintained during casting between 20-70 MPa and may subsequently be intensified up to 180 MPa.

Description

The present invention relates to a method for casting a magnesium alloy containing aluminum, zinc and manganese, the rest is magnesium and permanent impurities, while the total content of impurities is at a level less than a specified weight percentage.

Magnesium-based alloys are widely used in the automotive industry as a material for the manufacture of cast parts and, increasingly, in the ZS industry (computers, communications and consumer electronics). Magnesium-based cast alloys can be manufactured using conventional casting techniques, which include injection molding, sand casting, casting in permanent molds and semi-permanent molds, casting in plaster molds and investment casting.

Magnesium-based alloys have a number of particularly advantageous properties, which has led to an increase in demand for molded parts from magnesium-based alloys in the automotive industry. These properties include low density, high strength-to-mass ratio, good casting properties, good workability and good damping characteristics. The most common magnesium alloy casting alloys are alloys such as magnesium aluminum alloys or magnesium aluminum zinc alloys containing <0.5% Mn, mainly -§-9% Α1-1% Ζη (denoted as ΑΖ91), Md-6% A1 (AM60) and Md-5% A1 (AM50).

XVO 2006/000022 A1 describes a magnesium-based alloy containing zinc, aluminum, calcium and (or) beryllium or optionally manganese, with which an attempt was made to improve the surface finish quality of magnesium cast parts. However, this document is not specifically related to the casting properties of the alloy. The present invention provides a relatively inexpensive magnesium based alloy that provides improved surface finish quality and has improved casting properties.

The invention is characterized in that it proposed an alloy containing 10.00-13.00 wt.% Aluminum, 10.00-22.00 wt.% Zinc, and also containing 0.10-0.5 wt.% Manganese, the rest is magnesium and permanent impurities, the total content of which is less than 0.1 wt.%, while the alloy is cast in a mold, the temperature in which is regulated in the range of 150-340 ° C, is filled in the mold for a time which is in milliseconds the product of the number from 2 to 300 and the average thickness of the part in millimeters, maintain the static pressure of the metal during casting in the range of 20-70 MPa s in Possible subsequent increase to 180 MPa according to independent claim 1.

In dependent claims 2-11, preferred embodiments of the invention are described.

By combining the proposed magnesium-aluminum-zinc alloy with the above-mentioned special casting method, products with excellent surface finish, good ductility and acceptable mechanical properties, as well as corrosion resistance characteristics can be obtained.

The aluminum content is preferably from about 5.00 to 13.00 wt.%. When the aluminum content is less than 10.00%, the zinc content does not exceed 10.00-22.00 wt.%. With a lower zinc content, the combination of castability and surface finish quality deteriorates. When the aluminum content exceeds 10.00%, the zinc content limit can be extended to 0.00-22.00% with the preservation of satisfactory casting qualities and surface quality.

In applications where minimal ductility is required, the composition of the alloy is chosen so that the aluminum content is in the range from 10.00 to 12.00 wt.%, And the zinc content is from 0.00 to 4.00 wt.%. Alloys with equivalent casting qualities and surface finish quality can be obtained if an alloy composition is chosen in which the aluminum content is in the range from 6.00 to 12.00 wt.%, And the zinc content is from 10.00 to 22.00. weight.%. The advantage of these alloys is a lower casting temperature.

Further, the present invention is described by examples and with reference to the attached drawings, in which FIG. 1A, 1B schematically show die-casting machines with hot and cold pressing chambers, respectively;

in fig. 2 is a diagram illustrating the relationship between the solidification rate and the microstructure (grain size and distance between the secondary axes of dendrites) of cast magnesium alloys;

in fig. 3 is a diagram illustrating the relationship between grain size and ductility of magnesium alloys;

in fig. 4 is a diagram illustrating the relationship between grain size and tensile yield strength of magnesium alloys;

in fig. 5 is a diagram from the document of the prior art No. \ ν buss1ortsp15 ίη shadpesh bielezaypd, p.8. Roberg, notes 1MA, 1976, p. 35-39, in which the composition range is divided into a flowable area, a fragile area and an area of hot crack formation;

in fig. 6 - angle with a high content of magnesium in the phase diagram MD-A1 ^ n and the line of constant temperature of transition to the liquid state;

in fig. 7 is a diagram in which the relative solid content (wt.%) Is plotted on the horizontal axis depending on the temperature plotted on the vertical axis (° C) for three different magnesium alloy;

in fig. 8-10 - components of three different magnesium alloys, cast using three different molds;

in fig. 11 is a chart illustrating casting defects, average number of cracks and defective fins as illustrated in FIG. 8 flasks, which are shown in the diagram by lines of the same number of defects, with the zinc content along the x axis, and the aluminum content along the y axis;

in fig. 12 is a diagram illustrating the quality of surface treatment in the form of a gradation from 1 to 5 in the form illustrated in FIG. 8 opoka, which is shown in the diagram by lines of the same gradation, with the zinc content on the x axis, and the aluminum content on the y axis;

in fig. 13 is a diagram where the tensile strength in MPa is plotted along the axis, and the aluminum and zinc contents are shown along the x and y axes, respectively; plasticity is shown in the diagram by lines of equal relative elongation;

in fig. 14 is a diagram illustrating the corrosion rate in terms of weight loss, represented by lines equal to the corrosion rate (mg / cm ² / day), while the z-axis represents the zinc content, and the x-axis is the aluminum content.

FIG. 1A and 1B schematically show die-casting machines with hot and cold pressing chambers, respectively, each of which has a mold 10, 20, equipped with a system 11, 21 hydraulic clamping, respectively.

Molten metal using a shock cylinder 12, 22, equipped, respectively, with a piston 13, 23, is introduced into the mold. As shown in FIG. 1A, an auxiliary system is needed in the cold pressing chamber system for dispensing metal entering the horizontal shock cylinder. However, in the FIG. 1 In a hot pressing die casting machine, a system 12, 23 with a vertical piston is used directly in the molten alloy.

To obtain magnesium-aluminum-zinc alloys with excellent performance, the alloys must be cast under extremely rapid cooling. This concerns the method of injection molding. Steel mold 10, 20 is equipped with an oil (or water) cooling system that regulates the temperature in the mold in the range of 200-300 ° C. A prerequisite for ensuring high quality is the short filling time of the mold in order to avoid solidification of the metal during filling. The recommended time for filling the mold is of the order of 10 ^-2 s, multiplied by the average thickness of the part (mm). For this purpose, the alloy is forcibly supplied through a sprue with high speed in the range of 30-300 m / s. In order to provide the desired volumetric flows entering the shock cylinder with a short filling time, use plungers with a sufficiently large diameter and speed up to 10 m / s. Typically, the static pressure of the metal is 20-70 MPa with a possible subsequent increase in pressure to 180 MPa, especially in the case of castings with thicker walls. When using this method of casting the cooling rate of the product is usually 10-1000 ° C / s, depending on the thickness of the molded product.

FIG. 2 shows the relationship between the solidification rate and the microstructure of the cast alloy. The horizontal axis shows the rate of solidification (° C / s), the left vertical scale shows the distance between the secondary axes of the dendrites (μm), and the right vertical scale shows the grain diameter (μm). Line 30 is the resulting grain size, and line 31 is the resulting distance between the secondary axes of the dendrites.

In the case of die casting, the reduction in grain size is achieved due to the cooling rate. As mentioned above, cooling rates in the range of 10-1000 ° C / s are typically used. As a result, the grain size is usually 5-100 microns.

It is well known that the small grain size contributes to an increase in the plasticity of the alloy. This relationship is illustrated in FIG. 3, which shows the relationship between grain size and relative elongation. The average grain size (μm) is plotted along the horizontal axis, and the relative elongation (%) is along the vertical axis. The diagram shows two different compositions, line 35 denotes pure magnesium, and line 36 denotes magnesium alloy (91 (MD-9% A1, 1% η).

It is also well known that the small grain size contributes to an increase in the yield strength of the alloy under tension. This relationship (Hall-Petch) is shown in FIG. 4. The horizontal axis represents the grain diameter in b ^(-0.5) , while the value b is expressed in microns, and the vertical axis shows the yield strength in tension in MPa.

Thus, it is clear that the small grain size obtained at very high cooling rates, achieved by injection molding, is necessary to ensure the ultimate tensile strength and ductility.

The term casting quality means the ability to cast from the alloy of the finished product with the required functionality and properties. It usually includes three parameters: (1) the possibility of forming a product with the desired geometry and size, (2) the possibility of making a dense product with the desired properties and (3) the impact on the mold tooling, foundry equipment and the efficiency of injection molding. The 3C industry uses cast components with extremely

- 2014141 small wall thickness, such as the case of portable computers and mobile phones. This imposes mandatory requirements on the ability of the alloy to fill the mold and at the same time provide a smooth and shiny surface. Alloy grade ΑΖ91 is the most common alloy, applicable for this purpose, mainly due to its best casting properties compared to alloys of the brands AM50 and AM60. However, the surfaces of thin-walled components made of ΑΖ91 alloy often do not meet the requirements. Usually a conversion coating is applied to these components. With a less shiny surface, sometimes including areas with the segregation of elements, it is necessary to apply multiple layers of coating. Usually, the higher the surface quality, the less coverage is required.

Magnesium-aluminum-zinc alloys containing 0–10 wt.% Aluminum and 0–35 wt.% Zinc were studied in the 1970s. (№ \ ν бсус1ортсп15 ίη тадиеыит Ше сакйид, С.8. Eoeg, notes ΙΜΑ, 1976, p. 35-39). In the FIG. 5 of the diagram from Eoteck, the composition range is divided into a flowable area, a fragile area and an area of hot cracking. The alloys described in Australian patent application XVO 2006/000022 A1, which attempts to improve the quality of surface treatment, mainly fall within the flowable area shown in FIG. 5. The ranges of the compositions of the alloys according to the present invention are mainly outside the ranges of the compositions described in the prior art document (FIG. 5) and entirely outside the ranges described in νθ 2006/000022 A1. During the tests that are described later, it became clear that the alloys according to the present invention have significant advantages over the alloys described earlier in terms of filling the mold, sticking to the mold and the formation of hot cracks. All of these features are essential when casting complex thin-walled components.

Magnesium-aluminum-zinc alloys containing aluminum and zinc according to the present invention begin to harden at a temperature of about 600 ° C, depending on the content of aluminum and zinc. This is illustrated in FIG. 6, in which the MD-ΑΙ-Ζη phase diagram shows the lines of constant transition temperature to the liquid state for an angle with a high magnesium content. As a result, the casting temperature, usually 70 ° C higher than the transition temperature to the liquid state, can be significantly lower than that of conventional alloys AM50, AM60 and ΑΖ91. Due to the fact that the eutectic phase MD _g L1 | ₂ melts at a temperature of about 420 ° C, conventional magnesium-aluminum alloys, such as AM50, AM60 and ΑΖ91, will have a solidification interval of around 200 ° C, as shown in FIG. 7, on which the relative solid content (wt.%) Is plotted on the horizontal axis, depending on the temperature plotted on the vertical axis (° C) for three different magnesium alloys. In particular, alloy ΑΖ91 begins to harden at 600 ° C and fully hardens at 420 ° C. When the aluminum content increases to 14%, as in alloy ΑΖ141, solidification begins at a temperature of about 570 ° C and ends at 420 ° C. Due to the significant zinc content, alloy ΑΖ85 hardens in the temperature range 590-350 ° С. Since zinc in magnesium-aluminum-zinc eutectic alloy changes phase Μ§ ₁₇ Α1 ₁₂ alloy completely solidifies at temperatures significantly below 420 ° C as in the case of conventional alloys AM50, ΑΜ60 and ΑΖ91.

Usually, with an increase in the aluminum content of magnesium-aluminum alloys cast under pressure, the casting qualities of the casting are improved. This is due to the fact that magnesium-aluminum alloys have a wide range of hardening, which makes them naturally difficult to cast, unless a sufficiently large amount of the eutectic phase is present at the end of hardening. This can explain the good casting properties of ΑΖ91Ό, consistent with the cooling curves shown in FIG. 7. With a large amount of zinc in addition to aluminum in the proposed alloys, the amount of the eutectic (modified) phase present at the end of solidification increases even more, which explains the improved casting qualities of magnesium-aluminum-zinc alloys proposed in the invention.

In the molten state, magnesium alloys tend to ignite and oxidize (burn), unless they are protected by protective gases, such as 8E6, and dry air, with or without CO ₂ or 8O ₂ and dry air. Oxidation is exacerbated with increasing temperature. Usually, small amounts of beryllium (10-15 ppm by weight) are also added to reduce oxidation. Beryllium is known to form toxic substances and must be used with caution. Considerable precautions are required, in particular, in the processing of scale and slag formed during the cleaning of crucibles, since the scale / slag has a high content of beryllium compounds. One of the advantages of the present invention is that the casting of the alloy can be carried out at much lower temperatures than the casting of conventional alloys, thereby reducing the need for protective gases. For the same reason, beryllium supplements can be minimized.

Lower casting temperatures compared to conventional casting also provide significant advantages as the dosing system, impact cylinder and mold life increase. In particular, when casting under pressure using a hot pressing chamber, the service life of the tuyere hose is significantly increased. Alloys with lower temperature

- 3 014150 casting pits also have the potential to shorten the cycle time, thereby increasing the productivity of the injection molding process.

Example 1

In order to evaluate the effect of the alloy elements, several magnesium alloys were tested, which were cast in three different molds: the flask with ribs shown in FIG. 8, the plate / cassette mold shown in FIG. 9, a three plate mold shown in FIG. ten.

Next in the table. 1 shows the composition of the alloys and the casting temperature.

Table 1

A1 (% by weight) Ζη (% by weight) Casting temperature (C) A1 (% by weight) Ζη (% by weight) Casting temperature (C) AM20 2 0 710 ΑΖ85 eight five 670 ΑΖ21 2 one 710 AM90 9 0 670 ΑΖ22 2 2 705 ΑΖ91 9 one 670 -32-3.5 2 3.5 700 ΑΖ96 9 6 650 AM40 four 0 700 ΑΖ99 9 9 640 ΑΖ41 four one 695 ΑΖ9-12 9 12 620 ΑΖ42 four 2 695 ΑΖ9-18 9 18 585 ΑΖ4-3.5 four 3.5 690 ΑΖ9-22 9 22 560 ΑΖ45 four five 680 AM100 ten 0 660 ΑΖ4-14 four 14 650 ΑΖ10-1 ten one 660 ΑΖ4-18 four 18 630 ΑΖ10-2 ten 2 660 AM60 6 0 680 ΑΖ10-3.5 ten 3.5 650 ΑΖ61 6 one 680 ΑΖ10-5 ten five 650 ΑΖ62 6 2 680 AM120 12 0 650 ΑΖ63 b 3 680 ΑΖ12-1 12 one 650 ΑΖ6-3.5 6 3.5 680 ΑΖ12-2 12 2 640 ΑΖ65 6 five 670 ΑΖ12-3.5 12 3.5 640 ΑΖ66 6 6 670 ΑΖ12-5 12 five 630 ΑΖ6-12 b 12 640 ΑΖ12-6 12 6 630 ΑΖ6-18 b 18 610 ΑΖ12-12 12 12 590 ΑΖ71 7 one 680 ΑΖ12-18 12 18 550 ΑΖ72ΑΜ 7 2 680 AM140 14 0 640 AM80 eight 0 680 ΑΖ14-1 14 one 630 AM81 eight one 680 ΑΖ14-2 14 2 630 AM82 eight 2 670 ΑΖ 14-3.5 14 3.5 620 ΑΖ8-3.5 eight 3.5 670 ΑΖ14-5 14 five 610

In tab. 2 shows the detailed casting parameters.

table 2

Speed 1 (m / s) Speed 2 (m / s) Slowdown (m / s) Estimated fill time (msec) Press form one Tensile test specimen 0.5 five 3 50 Mold 2 Three plate 0.5 five 2.5 53 Mold 3 Flask 0.5 five 3 40

No increase in pressure was applied. The following tests were performed.

Casting defect evaluation

An external examination of ten randomly selected flasks was carried out with each alloy. Defects were grouped as follows:

defective fins, including incomplete filling and cold junctions, hot cracks counted at the nodes, face cracks.

Surface quality assessment

The quality of surface treatment was checked visually by several individuals individually and was assessed on a scale from 1 to 5 (5 is the highest rating).

Tensile strength and ductility

Samples were made for testing with a diameter of 6 mm according to the standard ΆδΤΜ V557M and tested in the following conditions:

Instron tensile testing machine, 10 kN, room temperature, at least 10 parallel clamps,

- 4 014150 strain rate of 1.5 mm / min with a strain of up to 0.5%, mm / min with a strain of more than 0.5%, tested according to the standard Ι8 6892.

Corrosion Resistance Characteristics

Corrosion resistance tests were carried out according to the standard A8TM B117.

Example 2

FIG. 11 illustrates casting defects, the average number of cracks and defective fins, which are shown in the diagram by lines of the same number of defects, with zinc content being deposited along the x axis, and aluminum content along the y axis. It can be seen that the smallest number of cracks is in areas with low (<3%) and high (> 10%) zinc content. It is seen that particularly good in terms of casting defects, alloys are obtained with an aluminum content in the range of 8–10 wt.% And a zinc content of <2 wt.%; the lower the zinc content, the better. Alloys with an aluminum content in the range of 7–12 wt.% And a zinc content in the range of 12–18 wt.% Also have a very small number of casting defects.

Example 3

FIG. 12 illustrates the quality of surface treatment in the form of a gradation from 1 to 5, which is shown in the diagram by lines of the same gradation, with the zinc content being deposited along the x axis and the aluminum content along the y axis. It is seen that the best in terms of surface quality are obtained with an aluminum content of> 11 wt.% And a zinc content of <3 wt.%; the lower the zinc content, the better. The area with an approximate aluminum content of 8–12 wt.% And a zinc content of> 10 wt.% Also corresponds to alloys with excellent surface finish.

Example 4

The strength and elongation at room temperature of several compounds were measured. The results are shown in FIG. 13. On the axis, the ultimate tensile strength is set in MPa, and on the x and y axes, the contents of aluminum and zinc, respectively. Plasticity is shown in the diagram by lines of equal relative elongation. In general, it can be seen that the tensile strength in MPa increases with increasing content of alloy elements. The effect of an increase in the aluminum content (wt.%) Significantly exceeds the effect of an increase in the zinc content. FIG. 13 also shows that with an increase in the content of alloy elements, ductility decreases in percent elongation. For example, a line indicating a 3% elongation runs almost straightforwardly from an aluminum content of 12 wt.% A1 and a zinc content of 0 wt.% To an aluminum content of 0 wt.% And a zinc content of 18 wt.%.

Example 5

The corrosion resistance characteristics of a number of compounds according to A8TM B117 were determined. When conducting this test, a large number of data was used to determine the effect of zinc content depending on the aluminum content. The results are shown in FIG. 14.

FIG. 14 is a diagram illustrating the corrosion rate in terms of weight loss, represented by lines equal to the corrosion rate (mg / cm ² / day), while the z-axis represents the zinc content, and the x-axis - the aluminum content. It can be seen that when the zinc content is less than about 8 wt.%, The corrosion rate decreases with increasing aluminum content and practically does not depend on the zinc content, and when the zinc content exceeds about 12 wt.%, The corrosion rate slightly increases with increasing zinc content and almost does not depend on aluminum content. The area of zinc content in 8-12 wt.% Is transitional. In particular, with a zinc content of 0%, the corrosion rate decreases from about 0.09 mg / cm ² / day, with an aluminum content of 4 wt.% To about 0.03 mg / cm ² / day, with an aluminum content of 9 wt.% . With a constant aluminum content of 9 wt.%, The corrosion rate increases to 0.05 mg / cm ² / day with a zinc content of 8 wt.% And to 0.11 mg / cm ² / day with a zinc content of 14 wt.%.

From these results it is clear that the proposed method of casting a magnesium alloy allows to obtain products with an improved combination of creep at elevated temperatures, ductility and corrosion characteristics.

Claims (11)

CLAIM 1. The method of casting magnesium alloy containing 2. The method according to claim 1, characterized in that the temperature in the mold support in the range of 160-300 ° C., Preferably in the range from 200 to 270 ° C. 3. The method according to claim 1 or 2, characterized in that the time of filling the mold in milliseconds is equal to the product of the average thickness of the part in millimeters and a number from 2 to 200, preferably from 3 to 50, most preferably from 3 to 20. 4. The method according to any one of claims 1 to 3, characterized in that the static pressure of the metal during casting is maintained in the range of 30-70 MPa. 5. The method according to any one of claims 1 to 4, characterized in that the cooling rate after casting is 10-1000 ° C / s. - 5 014150 maintains the static pressure of the metal during casting in the range of 20-70 MPa, with possible subsequent increase to 180 MPa. 5.00-13.00 wt.% Aluminum, 0.00-22.00 wt.% Zinc, and also containing 0.10-0.5 wt.% Manganese, the rest is magnesium and permanent impurities, the total content of which is less than 0.1 wt.%, During the implementation of which is cast the alloy in the mold, in which the temperature is maintained in the range of 150-340 ° C, is filled in the mold for a time, which in milliseconds is equal to the product of the number from 2 to 300 and the average thickness of the part in millimeters, 6. The method according to any one of claims 1 to 5, characterized in that the aluminum content is from 10.00 to 13.00 wt.%, Preferably from 10.00 to 12.00 wt.%. 7. The method according to any one of claims 1 to 6, characterized in that the zinc content is from 0.00 to 10.00 wt.%. 8. The method according to any one of claims 1 to 7, characterized in that the aluminum content is from 10.00 to 12.00 wt.%, And the zinc content is from 0.00 to 4.00 wt.%. 9. The method according to any one of claims 1 to 5, characterized in that the aluminum content is from 5.00 to 13.00 wt.%, Preferably from 6.00 to 12.00 wt.%. 10. The method according to any one of claims 1 to 5 and 9, characterized in that the zinc content is from 10.00 to 22.00 wt.%. 11. The method according to any one of claims 1 to 5 and 9, 10, characterized in that the aluminum content is from 6.00 to 12.00 wt.%, And the zinc content is from 10.00 to 18.00 wt.% .