Method for regulating the precipitation position of iron-rich intermetallic compounds using a magnetic field

Abstract

The application provides a method for regulating the precipitation position of iron-rich intermetallic compounds by using a magnetic field, and belongs to the technical field of material solidification and magnetic field application. The method comprises the following steps: melting an iron-rich alloy ingot and then rotating and solidifying the alloy ingot horizontally under a magnetic field. In the alloy solidification process, a magnetic field is applied, the thermal electromagnetic effect of the magnetic field is utilized to regulate the precipitation position of the iron-rich intermetallic compounds, after the magnetic field is applied, the iron-rich intermetallic compounds are only formed and grown on the oxide film at the edge of the alloy, and the intermetallic compounds formed on the surrounding oxide film can continuously obtain the solute required for growth and growth, which also leads to a low solute concentration in the center of the alloy, and the center of the alloy is basically free of intermetallic compound formation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material solidification and magnetic field application, and particularly relates to a method for regulating the precipitation position of iron-rich intermetallic compounds by using a magnetic field. BACKGROUND

[0002] Aluminum alloys have good mechanical properties and corrosion resistance, and are widely used in the fields of machinery, aviation and the like. However, during the casting and recycling of aluminum alloys, iron impurities inevitably occur, which are difficult to remove. The internal trace iron impurities in Al-Si alloys can cause the formation of hard and brittle intermetallic compounds such as α-Al8Fe2Si and β-Al5FeSi. When the internal iron element content of the alloy is relatively high, the brittle plate-like β-Al5FeSi phase is the main precipitate in the alloy, and is precipitated in the internal alloy. These β phases are the main positions of crack formation, which have adverse effects on the casting performance, machining performance and final mechanical properties (especially ductility) of the alloy.

[0003] Therefore, how to control the position of the precipitated phase of the alloy, reduce or avoid the precipitation of the precipitated phase in the internal alloy, and improve the performance of the alloy have become problems in the prior art. SUMMARY

[0004] The present application relates to the technical field of material solidification and magnetic field application, and particularly relates to a method for regulating the precipitation position of iron-rich intermetallic compounds by using a magnetic field.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0006] The present application provides a method for regulating the precipitation position of iron-rich intermetallic compounds by using a magnetic field, comprising:

[0007] The iron-rich alloy ingot is melted and then horizontally rotated and solidified under a magnetic field.

[0008] Preferably, the mass fraction of iron in the iron-rich alloy ingot is 0.5-1.5%.

[0009] Preferably, the melting temperature is 750-850℃.

[0010] Preferably, the holding time of the melting is 20-40 min.

[0011] Preferably, the heating rate for heating to the melting temperature is 10-20℃ / min.

[0012] Preferably, the direction of the magnetic field is horizontal.

[0013] Preferably, the strength of the magnetic field is 0.05-9T.

[0014] Preferably, the horizontal rotation rate is 180° / 40~60s.

[0015] Preferably, the cooling rate during solidification is 2 to 4 K / min.

[0016] This invention provides a method for controlling the precipitation location of iron-rich intermetallic compounds using a magnetic field, comprising melting an iron-rich alloy ingot and then horizontally rotating and solidifying it under a magnetic field. In this invention, the iron-rich alloy ingot is melted and solidified under the action of a magnetic field. During solidification, due to the decrease in temperature, the alloy solidifies radially. The intermetallic compounds and the surrounding liquid have different compositions, resulting in a Seebeck effect. The temperature at the tip of the intermetallic compound may be significantly higher than its bottom, thus forming a non-isothermal interface and generating thermo-electromagnetic currents. These thermo-electromagnetic currents act on the interface near the melt at a microscale. Thermo-electromagnetic convection also causes directional flow in the melt. When only a transverse magnetic field of the same direction is applied, the transverse static magnetic field promotes the flow of the liquid phase, generating unidirectional thermo-electromagnetic flow. This causes Fe to migrate along the liquid flow direction, resulting in Fe solute enrichment on one side of the sample. This allows the intermetallic compounds initially formed at the sample edge to continuously acquire solute and grow, thus forming coarse, plate-like intermetallic compounds segregated on one side of the sample. When using the method of this invention, the sample is continuously rotated, and the Fe solute continuously moves towards the sample edge (previously it moved to one side). At this time, the intermetallic compounds formed on the oxide film at the sample edge can continuously acquire the Fe solute required for growth. This also results in a lower Fe solute concentration in the sample center, and virtually no intermetallic compounds forming in the sample center. Attached Figure Description

[0017] Figure 1 This is a physical diagram and an internal schematic diagram of the apparatus used in the method of controlling the precipitation location of iron-rich intermetallic compounds using a magnetic field, as described in this invention.

[0018] Figure 2 This is an X-ray image of the solidified sample after a magnetic field was applied in Example 1 of the present invention.

[0019] Figure 3 This is a 3D reconstruction image of a solidified sample after applying a magnetic field in Example 1 of the present invention, obtained by CT.

[0020] Figure 4 A schematic diagram showing the precipitation sites of intermetallic compounds when a magnetic field is applied in this invention;

[0021] Figure 5 This is an X-ray image of the solidified sample of Comparative Example 1 of the present invention without a magnetic field.

[0022] Figure 6 This is a 3D reconstruction image of the solidified sample of Comparative Example 1 of the present invention without a magnetic field after CT.

[0023] Figure 7 This is a schematic diagram showing the precipitation locations of intermetallic compounds when no magnetic field is applied, according to the present invention. Detailed Implementation

[0024] This invention provides a method for controlling the precipitation location of iron-rich intermetallic compounds using a magnetic field, comprising:

[0025] The iron-rich alloy ingot is melted and then solidified by horizontal rotation under a magnetic field.

[0026] Unless otherwise specified, the present invention does not impose any special restrictions on the source of the raw materials, and commercially available products well known to those skilled in the art can be used.

[0027] The present invention preferably involves smelting the alloy raw materials to obtain iron-rich alloy ingots.

[0028] In this invention, the alloy is preferably an Al-Si-Fe alloy.

[0029] In this invention, the mass fraction of Si in the Al-Si-Fe alloy is preferably 8-12%, more preferably 10%.

[0030] In this invention, the mass fraction of iron in the iron-rich alloy ingot is preferably 0.5-1.5%, more preferably 1%.

[0031] In this invention, the alloy raw materials preferably include pure iron, pure aluminum, and an Al-12wt%Si-0.2wt%Fe master alloy.

[0032] In this invention, the melting temperature is preferably 650–850°C, more preferably 700–800°C; the invention preferably involves holding the alloy raw material at this temperature after it has completely melted; the holding time is preferably 5–15 min, more preferably 10 min. The invention preferably involves stirring during the holding process; the stirring rate is preferably 200–400 rpm, more preferably 300 rpm. By limiting the melting temperature, time, and stirring rate within the above ranges, this invention enables a more uniform distribution of the solute in the alloy, resulting in a fine and uniform primary Si phase and a dense matrix structure.

[0033] In this invention, the smelting is preferably carried out in high-purity argon gas. The high-purity argon gas protects the alloy, preventing oxidation and contamination.

[0034] In this invention, the smelting is preferably carried out in a vacuum medium-frequency induction furnace. Prior to smelting, high-purity argon gas is preferably used for gas washing to remove impurities and oxygen.

[0035] After smelting, the present invention preferably cools, cuts, grinds, washes and dries the smelted product in sequence to obtain an iron-rich alloy ingot.

[0036] The present invention does not impose any particular limitation on the cooling method; any smelting cooling method known to those skilled in the art can be used.

[0037] In this invention, the cutting is preferably performed using wire electrical discharge machining to cut round bars with a diameter of 2-4 mm and a length of 50-70 mm, more preferably into round bars with a diameter of 3 mm and a length of 60 mm. In this invention, the round bar structure is more suitable for rotation to ensure that the magnetic field is applied uniformly during rotation, thereby obtaining more accurate results.

[0038] The present invention does not impose any special limitations on the polishing operation; any polishing operation known to those skilled in the art can be used.

[0039] In this invention, the washing process preferably includes, in sequence, alkaline washing, water washing, and organic solvent washing.

[0040] In this invention, the alkaline solution used for alkaline washing is preferably a sodium hydroxide solution, potassium hydroxide solution, or sodium carbonate solution; the mass concentration of the alkaline solution is preferably 5-15%, more preferably 10%; the temperature of the alkaline washing is preferably 70-90℃, more preferably 80℃; and the washing time is preferably 20-40 minutes, more preferably 30 minutes. This invention does not have a specific limitation on the amount of alkaline solution used, as long as it is sufficient to submerge the iron-rich alloy ingot. In this invention, the alkaline washing is used to remove residues after electrical discharge machining (EDM).

[0041] The present invention does not impose any special limitations on the water washing operation; any water washing technical solution known to those skilled in the art can be used.

[0042] In this invention, after the water washing is completed, the surface of the alloy ingot is preferably inspected using a microscope to confirm whether there are any residual ablation marks or oxide scale; if so, the alkaline washing and water washing are preferably repeated. This invention does not have a specific limit on the number of alkaline washing and water washing cycles, as long as it ensures that there are no residual ablation marks or oxide scale on the surface of the alloy ingot.

[0043] In this invention, the organic solvent used for washing is preferably one or more of acetone and alcohol; the organic solvent washing is preferably ultrasonic washing; the ultrasonic power is preferably 50-200W, more preferably 100-150W; the ultrasonic time is preferably 10-30min, more preferably 15-20min. In this invention, the organic solvent washing can further remove residues after cutting.

[0044] In this invention, the drying temperature is preferably 90-110°C, more preferably 100°C; the drying time is preferably 1-3 hours, more preferably 2 hours.

[0045] After drying, the present invention preferably places the dried product in a dry environment to avoid reaction with moisture or other substances in the air.

[0046] After obtaining the iron-rich alloy ingot, the present invention melts the iron-rich alloy ingot and then solidifies it by horizontal rotation under a magnetic field.

[0047] In this invention, the melting temperature is preferably 750–850°C, more preferably 780–820°C; the holding time for melting is preferably 20–40 min, more preferably 30 min; and the heating rate to the melting temperature is preferably 10–20°C / min, more preferably 15°C / min. By limiting the melting temperature and time to the above ranges, this invention ensures the complete melting of the iron-rich alloy ingot.

[0048] In this invention, the direction of the magnetic field is preferably horizontal; the strength of the magnetic field is preferably 0.05–9 T, more preferably 0.05–5 T, and most preferably 0.05–1 T. By limiting the direction and strength of the magnetic field within the above ranges, this invention enables the iron-rich intermetallic compound to flow sufficiently to the edge of the melt.

[0049] In this invention, the rate of horizontal rotation is preferably 180° / 40–60 s, more preferably 180° / 50 s. In this invention, the rotation ensures that the iron-rich intermetallic compounds formed during solidification move to the edge of the alloy.

[0050] In this invention, the cooling rate during solidification is preferably 2 to 4 K / min, more preferably 3 K / min. By limiting the solidification rate within the above range, this invention enables the iron-rich intermetallic compound to have a smaller size.

[0051] This invention does not impose any particular limitation on the solidification apparatus; it can be selected according to actual needs. In this invention, the physical and schematic diagrams of the solidification apparatus are preferably as follows: Figure 1 As shown, a resistance furnace with two independent heaters is used. The furnace has a central hole for inserting and rotating iron-rich alloy ingots. The iron-rich alloy ingots are preferably placed inside boron nitride tubes before being inserted into the furnace's central hole. The center of the furnace's outer surface has a 10mm high and 20mm wide window made of boron nitride (BN) to allow X-ray penetration and facilitate subsequent inspection. Two thermocouples and one magnet are installed on the sidewall of the furnace's central area. The thermocouples are used to control the temperature, and a measuring thermocouple is placed at the top and bottom of the furnace to measure the internal temperature.

[0052] A preferred schematic diagram of the precipitation sites of intermetallic compounds when a magnetic field is applied according to the present invention is shown below. Figure 4 As shown, the iron intermetallic compounds are distributed in the red annular shaded area under the influence of a magnetic field; the preferred location of the intermetallic compounds when no magnetic field is applied is shown in the diagram. Figure 7 As shown. From Figure 4 and 7 As can be seen, when a magnetic field is applied, during the rotation process, the thermo-electromagnetic effect of the magnetic field affects the diffusion of intermetallic compounds and the distribution of primary phases in the alloy, thereby regulating the distribution of intermetallic compounds.

[0053] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0054] Example 1

[0055] (1) Using industrial pure iron, pure aluminum and Al-12wt.%Si-0.2wt.%Fe as raw materials, put them into a corundum crucible according to the composition ratio of Al-10wt.%Si-1wt.%Fe alloy, and then put them into a vacuum induction furnace. The furnace is cleaned with high-purity argon gas, and then heated to 700℃ for melting. After the raw materials are completely melted, they are stirred at 300rpm for 10min by magnetic stirring. After cooling, alloy ingots are obtained. The entire melting process is carried out under high-purity argon gas conditions.

[0056] (2) The alloy ingot was cut into round bars with a diameter of 3 mm and a length of 60 mm by wire electrical discharge machining. After the surface was polished with sandpaper, it was placed in a 10% NaOH solution and kept at 80°C for 30 min. Then it was washed with water and dried. The surface was examined under a microscope and no residual ablation marks or oxide scale were found. It was placed in an oven at 100°C for 2 h. Then it was placed in acetone and ultrasonically washed at 100W power for 15 min. Then it was dried and placed in a boron nitride tube with an inner diameter of about 3 mm and an outer diameter of about 6 mm.

[0057] (3) Place the boron nitride tube containing the alloy ingot into the center hole of the resistance furnace and rotate it at a rate of 180° / 50s. Heat the furnace to 750°C at a rate of 15°C / min, apply a horizontal magnetic field of 0.07T, hold for 30min, and then cool at a rate of 3K / min until the sample is completely solidified.

[0058] Comparative Example 1

[0059] The magnetic field in Example 1 is omitted, and all other parameters are the same as in Example 1.

[0060] The cured alloy sample of Example 1 was observed using X-rays, and the results are as follows: Figure 2 As shown, Figure 2 The upper image shows an X-ray image of a section, and the lower image shows an X-ray image of a side view. The sample is a round rod. The upper image is equivalent to cutting the rod in half to observe the distribution of intermetallic compounds, and the lower image is equivalent to cutting the rod from top to bottom along the diameter of the circle to observe the distribution of intermetallic compounds in the cut surface. The image of the alloy sample from Example 1 after CT 3D reconstruction is shown below. Figure 3 As shown, from Figure 3 The distribution of intermetallic compounds in the sample can be seen in the images. The top image shows the sample viewed from above, and the bottom image shows it viewed from one side. X-ray observation was performed on the cured alloy sample of Comparative Example 1, and the results are as follows. Figure 5 As shown, Figure 5 The upper image shows an X-ray image of a slice, and the lower image shows an X-ray image of a side view. The image of the alloy sample in Comparative Example 1, reconstructed using CT, is shown below. Figure 6 As shown, from Figures 2-3 , Figures 5-6 As can be seen, when there is no magnetic field, the intermetallic compounds are randomly generated in the sample and cover the entire sample. However, when a magnetic field is applied, the intermetallic compounds only form and grow on the surface of the oxide film of the sample, with almost none in the central part.

[0061] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for controlling the precipitation location of iron-rich intermetallic compounds using a magnetic field, comprising: The iron-rich alloy ingot is melted and then solidified by horizontal rotation under a magnetic field. The iron-rich alloy ingot contains 0.5% to 1.5% iron by mass. The direction of the magnetic field is horizontal; the strength of the magnetic field is 0.05~9T; and the speed of the horizontal rotation is 180° / 40~60s.

2. The method according to claim 1, characterized in that, The melting temperature is 750~850℃.

3. The method according to claim 1 or 2, characterized in that, The holding time for melting is 20-40 minutes.

4. The method according to claim 2, characterized in that, The heating rate to the melting temperature is 10~20℃ / min.

5. The method according to claim 1, characterized in that, The cooling rate during solidification is 2~4 K / min.

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