With the development of science and technology, automotive, shipbuilding, aerospace, aerospace and other manufacturing industries have increasingly higher quality requirements for aluminum alloy castings. In addition to ensuring chemical composition, mechanical properties and dimensional accuracy, castings are not allowed to have porosity and shrinkage. Holes and other defects. The smelting of aluminum alloys is a very important process in the production process of castings. The production experience over the years proves that the smelting process is not strictly controlled and the castings are prone to defects such as pinholes, oxidized slag, and shrinkage, which directly affect the quality of castings. Therefore, in order to obtain high-quality aluminum alloy castings, the smelting process must be strictly controlled.
First, preparation before smelting 1 strict control of the charge quality. Burden quality is the source of foundry production and directly affects the quality of the final castings. The unqualified composition leads to scrapping of the product. therefore,
It should be highly valued.
Must do: 1 strictly control the proportion of new and old charge materials in the charge, the percentage of the mass of the charge returned to the charge should be less than or equal to 70%; 2 ensure that the charge is clean, the charge needs to be used after blowing sand; 3 the third return charge is poured It should be remelted and refined before use; 4 The burden should be fully preheated to remove impurities such as water, oil, etc. 5 As Ming alloys are aluminum-silicon, aluminum-copper, aluminum-magnesium and other alloys, more alloys are used, the elements used are Also more, and affect each other, require strict management, can not mix; 6 ingredients, weighing to be accurate, such as ZL104 alloy, taking into account the degassing, slagging and deterioration in the process of loss, Mg elements should be added in the actual ingredients 0.02%-0.03% of the charge quality guarantees the chemical composition of the casting.
2 smelting tools. The melting point and smelting tool used for smelting must be cleaned and painted to ensure that they are effectively separated from the aluminum alloy during use, and the alloy fluid is reduced from contamination by impurities. It needs to be fully preheated, and the material must be baked to dark red before charging. Smelting,
Water vapor is introduced into the alloy to increase the alloy gas and increase the pinhole degree.
3 other work. The preparatory work for covering agents, refining agents and modifiers should be done in strict accordance with the established process specifications.
Second, the smelting operation smelting steps are as follows.
1 charge. In the preheated Mandarin A, it is filled with pre-cast alloy ingots and high-quality recycled materials.
Plus in the fol alloy, and finally add alloying elements.
2 temperature control. Strictly control the melting temperature of the aluminum alloy, only the right temperature can obtain high-quality alloy liquid, avoid overheating. If the temperature is too high, the oxidation loss of various elements in the alloy will increase, causing changes in the chemical composition of the alloy. If the temperature is too low, the chemical composition of the alloy will be non-uniform, and the inclusions, gases, etc. in the alloy will not be easily discharged, and the physical and chemical properties of the alloy will be degraded, which will affect the casting performance.
3 time control. Strictly control the melting time, the operation should be rapid, reduce the alloy suction and oxidation inclusions, increase the burning of alloying elements, affect the chemical composition of the alloy.
4 refining operation. The main purpose of aluminum alloy refining is to remove gases and non-metallic inclusions and uniform alloy components in the melt. Refining is a very important process in smelting. The refining agent should be selected correctly, the addition of 0.5%-0.7% of the mass of the added alloy should be controlled, and the refining temperature should be controlled. The refining temperature is generally controlled at 700-
7200C. In the refining process, the refining agent is pressed in batches into about 2/3 of the molten surface with a bell jar
At the same time, you should press the orange rhyme at the bottom, and rotate it evenly and clockwise. The speed should be slow and the movement must be steady to avoid stirring the molten metal to prevent it from increasing its hydrogen content and being involved in inclusions.
5 metamorphic treatment. The purpose of metamorphism of the alloy is to refine the grains and improve the performance of the casting. The modifier should be preheated. The main points of control are: 1 metamorphic temperature, generally not exceeding
7400C; 2 metamorphic time, generally 10min; 3 the amount of modifier added, the amount of use of two-color modifier is generally 1.0% -1.2% of the quality of the alloy; 4 operating methods should be in place. After the alloy is refined, it must be poured as soon as possible. Sand casting should generally be controlled
In 40min, the metal mold casting should be controlled within 2h, otherwise, it is necessary to re-refining,
As a result of deterioration, the refining agent added at the time of refining is about 0.2% of the alloy mass.
(Precautions. To prevent aluminum splashing, the smelting site should be kept dry; operators should wear anti-radiation glasses, work caps, gloves, and overalls.
Three, two key issues 1 The mechanical properties of single-cast test bars cannot fully reflect the quality of smelting.
The performance of a single-cast test bar can only represent part of the smelting quality and heat treatment quality. The amount of gas contained in the aluminum liquid, the size of the shrinkage and oxidation tendency, and the content of the slag inclusions cannot be fully reflected in the mechanical properties of the single-cast test bars.
2 Effects of several elements on the microstructure and properties of aluminum alloys. In actual production, it was found that when the content of Mg in the aluminum alloy is close to the lower limit of the standard, the hardness of the casting may be reduced, and when the standard upper limit is approached, the elongation may be reduced; the Ti element is the most commonly used refiner in the aluminum alloy. , beneficial to alloy smelting; Fe element is the main harmful impurities in the alloy, will reduce the mechanical properties of the alloy, it comes from the citrus, smelting tools and charge, should be strictly controlled; Mn element can effectively reduce the Fe element harmful to the aluminum alloy Impact, but the amount of Mn added should not be too much, otherwise it is easy to produce large brittle compounds, and may also produce segregation, affecting the performance of castings.
IV. Analysis and Prevention of Defects Caused by Smelting
1. Pin hole defects caused by aluminum alloy pinholes: 1 charge and smelting tools baking is not sufficient;
2 the melting temperature is too high or the smelting time is too long; 3 the molten aluminum stays for a long time after the deterioration;
4 Alloy refining is not good; 5 Workplace is too humid.
Preventive measures: 1 charge and tools should be thoroughly dried; 2 control the melting temperature, generally does not exceed 7400C, does not exceed the pouring temperature, but also to prevent the local overheating of the alloy in the melting process; 3 rapid operation, minimize the smelting time; 4 refining Operation must be careful,
Refining is the best way to prevent blowholes; 5 After the metamorphic alloy is allowed to stand for 8-15min should be cast in time; 6 Keep the smelting site dry.
2. Oxidized slag aluminum oxide slag slag defects caused by the reasons: 1 charge is not clean, return material consumption too much; 2 alloy liquid slag is not removed clean; 3 after the deterioration of treatment, standing time is not enough.
Preventive measures: After the charge is blown, the charge is controlled within 70% of the charge quality. The degassing and slag removal must be thorough. After the deterioration, sufficient time for standing is ensured so that the slag has enough time to sink or float.
3. Shrinkage and shrinkage defects Aluminum alloy shrinkage and shrinkage defects caused by: 1 alloy grain coarse; 2 tricks alloy casting temperature is too high; 3 cast casting system design is unreasonable.
Preventive measures: (1) The effect of alloy liquid refining and metamorphic operation has a great influence on this type of defect; therefore, it must be in place; (2) strictly control the temperature of the molten aluminum to prevent overheating; in the case of ensuring that the casting does not produce insufficient water, it should be adopted as much as possible. Low pouring temperature, casting temperature generally does not exceed 7300C; 3 rational design of the casting system, so that the metal liquid can be filled smoothly; 4 appropriate adjustment of the composition, control of the appropriate impurity content to enhance the liquid metal flow is also effective.
5. Control measures of Mg elements in the smelting process of ZL 104 alloys. It is particularly important to prevent the burning of alloying elements in the smelting process. ZL104
In the melting process of aluminum alloys, the loss of Mg is more difficult to control than the loss of other components. In order to reduce the burning of Mg elements, it is necessary to strengthen the control of the melting process. This section focuses on
The ZL104 example discusses in detail the control of the aluminum alloy smelting process, especially the aluminum alloy in the high temperature state and the refining, metamorphic stage of the control.
ZL104 aluminum alloy belongs to Al-Si binary eutectic alloy added Mg AI-Mg-Si
Casting alloys, in the defense industry and civilian products, casting aluminum alloy ZL104 widely used, its composition (mass fraction) Si8.0% -10.5% "M four.17% -0.3%
MnO.2% -0.5%, the rest are Alo ZL104 alloy castings are generally used in the T6 state, because Mg and Si form a hard and brittle M protection phase, it is the most sensitive to the heat treatment effect of the alloy. When the alloy is solution-treated and then aged at 150-180°C, the dispersive Mg2Si particles are precipitated from the solid solution of the a-matrix, causing the lattice to undergo a catastrophic transformation, impeding the movement of dislocations and strengthening the alloy. The tensile strength has greatly improved and even reached a peak. However, a small amount of Mg does not enhance it.
Excessive Mg will have a large amount of Mg2Si, which affects the plasticity of the alloy. In practice, it was found that when the Mg content is close to the lower limit of the material standard, the hardness is generally low and the elongation is high; and when the Mg content is close to the upper limit of the material standard, the general elongation is low and may not meet the requirements.
Years of production practice show that the smelting process is the key process in the production process of such material castings. This process is a guarantee of physical and chemical properties. A slight oversight may lead to scrapping of the entire furnace component due to unqualified chemical composition. Among the elements that play a key role is the Mg element in the composition. Repeated practice has proven that because Mg elements are relatively lively, coupled with various aspects of burning factors, it is not easy to control in production. Therefore, how to improve the quality of ZL104 alloy in the smelting process is a key issue for producing ZL104 alloy castings.
There are many factors that affect the Mg element in the ZL104. Mg is an active element with a melting point of 650° C. and a strong affinity for oxygen. The oxidation rate is greatly enhanced when in the liquid state. During the refining and metamorphic process, the burning of Mg elements will increase, the time of heat preservation and pouring will be too long, and the loss of Mg elements will increase.
1. Ingredients The proportion of Mg elements should be given special emphasis on the proportions of new and returned materials. In the charging ratio of the charge, it is necessary to adopt the method of "de-tailing". For example, if the content of Mg in the recycled material is 0.1484%, our usual algorithm is to retain two digits after the decimal point.
The third digit adopts the method of 'rounding'. At this time, 0.1484% is even considered as
0.15%. This calculation equals 0.0016% of Mg in the return charge, and 0.0016% of Mg in the mix. However, considering the large amount of loss of Mg in the smelting process, regardless of the third digit, the actual figure of the second digit shall prevail, which is 0.14% to calculate its Mg content. The facts show that the charge smelting effect calculated by this method is qualified.
2. The purpose of the refining process is to remove non-metallic inclusions in the alloy fluid.
There are many methods for refining, among which hexachloroethane (C2CQ degassing refining is more commonly used.
At a temperature of 700-720°C, the refiner C plant 16 is pressed in batches into about 2/3 of the melt surface with a bell jar.
Evenly and slowly, rotate clockwise until C2Ch reacts fully and brings out inclusions and gases in the melt. The main point is that the speed of stirring is slow, if the frequency of stirring is too large, C2CL6
The reaction in the molten aluminum is fierce, the melt constantly tumbling, and the magnesium in the melt is in large contact with oxygen.
Burning occurs, which increases the amount of burns and may cause a drastic reduction in the amount of magnesium.
C2CI. The amount used is related to the alloy composition and the quality of the original ingot, but also related to the Mg content.
The general amount is 0.5%-0.7% of the charge quality. When the melting time is less than 10 minutes, the Mg loss is 0.02%-0.05% of the charge quality.
3. Drossing When the C2CL is fully refined, the bell jar is removed, the residual oxide is removed, and the inclusions on the surface of the molten metal are removed with a slag scoop. At a temperature of 680-700°C, the Mg is placed in a bell jar and pressed into the lower part of the melt.
5min. After Mg is completely melted in the melt, it is slowly stirred clockwise to make it evenly distributed in the alloy. It cannot allow the tumbling melt to break through the liquid surface, so as to prevent Mg from floating on the liquid surface to cause oxidative combustion and reduce the actual content of Mg. . The entire operation process must be careful and stable.
4. Metamorphic process According to the alloy smelting process, the mass ratio of Si in the Al-Si alloy is 6%-11%.
The alloy is easy to produce coarse-grained silicon after casting, and it should be modified after refining in sand casting or metal casting. To refine grains, when using sodium-based quaternary modifiers,
The amount is generally about 2.5% of the mass ratio of the charge, it should be preheated at the hearth for 5-10min.
Let it evaporate as much as possible. When the alloy temperature reached 720-740°C, the modifier was pressed into the surface of the alloy, gradually melted to produce a metamorphic effect, and then allowed to stand. The entire operation time is 8-12 minutes. During the pouring process, there is no need to remove the slag from the modificator, and only the modificator can be pushed aside and the alloy liquid can be poured to ensure the metamorphic effect from beginning to end. In this process, the burning of Mg elements is larger than in the refining stage. The loss of Mg is 0.13%-0.18% of the mass ratio of the charge. The relatively high temperature of the alloy liquid and the large amount of contact with the sodium salt and the active sodium element contribute to the long-term oxidation of the Mg element. Therefore, the metamorphism process is the main stage of the loss of the Mg element.
5. Casting process 4-10min after the deterioration of the alloy should be cast immediately. The pouring temperature is generally required to be between 730-745°C. Practice has proved that when the temperature is above 750°C, it will accelerate the oxidation of aluminum, and the burning of magnesium will also accelerate. Therefore, the pouring temperature must be strictly controlled. According to the production characteristics of the casting, the temperature is controlled at 740750°C at the beginning of pouring. between,
Because the temperature of the sand or metal mold is low at this time, defects such as insufficient pouring of the final cast parts are avoided. Can not arbitrarily extend the standing time, which will increase the burning of magnesium elements, resulting in unqualified chemical composition, the general sand casting requirements within 40min pouring, metal mold casting in 2h finished. Otherwise, it should be re-refined and deteriorated. The bottom of the orange juice contains a lot of impurities, should be left 1/151/10 of the volume of the site do not cast parts.
ZL104 aluminum alloy castings can ensure the quality of metallurgy through the above-mentioned several controls in the smelting process.
The operation point of melting Z L303 with medium-frequency induction electric furnace starts the intermediate frequency generator set and preheats the intermediate frequency furnace to about 500°C.
2 After the charge material is completely melted, heat up to 680-70000, press the magnesium block into aluminum liquid with a bell jar, and stir slowly to make it completely melted.
After the 3 magnesium blocks are completely melted, continue heating up to 710-.7200C, and remove the covering agent.
Add C2C'6, which is about 0.7% of the total mass of the charge, and mix it evenly with N2SiF6 at a ratio of 3:2, and refine the degassing with aluminum foil.
4 After refining, sprinkle evenly with the newly removed coating agent and a small amount of Ca.
3- 5min, press into the aluminum liquid with a pressure scoop.
5 Open the scum and take samples for fracture inspection. If the fracture is clean and smooth,
Crystal density, the alloy smelting qualified.
ZL303 alloy is easy to oxidize. When smelting with medium frequency furnace, due to longer smelting time, it must be strictly controlled at the furnace temperature.
VII. Smelting process of ZL101 alloy
1, smelting preparation 1 cleaning furnace and washing furnace (resistance furnace or frequency ignition.
2 Preheat the citrus vortex and smelting tool to 200-3000C, then spray paint.
3 Clean and preheat the charge.
4 prepare flux.
5 Ingredients calculation, due to the large loss of Si and Mg in the smelting, the composition of the alloy changes greatly, so the ingredients should be calculated according to the upper limit of the standard composition.
2. The charge charging sequence is: return charge, Al-Si master alloy or ZL102 alloy,
Pure aluminum ingots.
3. After melting and refining the burden is complete, it warms and melts. After the charge is completely melted, the residue is removed and the flux is added. When the temperature reaches 680°C, the metal magnesium block or Al-Mg master alloy preheated to 200-300°C is pressed into a certain depth of the bath with a bell jar and slowly turned and moved.
The time is 3-5min. Then increase the %} ill 730-75O t, with a total mass of 0.7% of the charge
0.75% of C2C1. 2-3 times with a bell jar pressed into the alloy liquid refining alloy liquid, the total time is 10-15min, slowly burning in the furnace. After the completion of refining is allowed to stand for 1-2min, samples are taken for pre-furnace analysis.
4. Modification treatment When the temperature of the alloy liquid reaches 730-750°C, the total mass of the charge is 1.5%-2.5%
The three-way metamorphic agent is subjected to a modification treatment, and the metamorphic time is 15-18 min.
5. Casting When the deterioration is completed, the slag is removed and stirred, and then allowed to stand for 5 - 10 minutes. When the temperature reaches
At 760°C, the slag is poured out.
VIII. Smelting process of Z L203 alloy
Smelting preparation 1 cleaning furnace and washing furnace (resistance citrus vortex furnace or mid-frequency induction P).
2 Preheat the citrus vortex and smelting tool to 200-30000, then spray paint.
3 Clean and preheat the charge.
4 Preparation of flux and modifiers.
5 é…‰ has been calculated.
2. The charge charging sequence is: return charge, pure aluminum ingot, Al-Cu master alloy.
3. After melting and refining the burden is complete, it warms and melts. After the charge is completely melted, the residue is removed and the flux is added. When the temperature reaches 690-720°C, chlorine, hexachloroethane, manganese chloride,
A refining agent such as zinc chloride refines the alloy solution. After completion of refining, let stand 1 -' 2min, take the sample for furnace analysis and composition adjustment.
4. Modification treatment When the temperature of the alloy liquid reaches 710-730°C, the total mass of the charge is 1.5%-'2.5%.
The three-way metamorphic agent is subjected to a modification treatment, and the metamorphic time is 15'-18 min.
5. Pouring When the deterioration is completed, the residue is removed and stirred, and then allowed to stand for 5-10 minutes. When the temperature reaches
At 780°C, the slag is poured out.
Nine, Z L401 alloy melting process
1 smelting preparation 1 cleaning furnace and washing furnace chaos resistance furnace or intermediate frequency P).
2 Preheat mandarin A and smelting tool to 200-30000, then spray paint.
3 Clean and preheat the charge.
4 Preparation of flux and modifiers.
5 Ingredients calculation, due to the large loss of Mg in the smelting, the composition of the alloy changes greatly, so the ingredients should be calculated according to the upper limit of the standard composition.
2. The sequence of charging and charging is: return charge, Al-Si master alloy or ZL102 alloy, pure aluminum ingot, and the ingot charge is melted at 660°C after melting.
3. After melting and refining the burden is complete, it warms and melts. After the charge is completely melted, remove the slag and gently stir the alloy solution for 3-5 turns. When the temperature reaches 660°C, use bell jar to preheat to 150-
250 °C metal zinc block press, until the zinc block is fully melted 1 - 3min, adding flux,
Immediately, the metal magnesium block or Al-Mg master alloy was pressed into a certain depth of the bath with a bell jar and slowly slewed and moved for 3 - 5 minutes. Then warm up to 710-7300C,
Use C2Ch or 0.1%--0.15% MnCl: 0.3%-0.5% of the total mass of the charge
2-3 times with the bell into the alloy liquid refining, the total time is 10-15min, slowly burning in the furnace. After the refining is completed, it is allowed to stand for 1 - 3 minutes, and the sample is taken for analysis and adjustment of the components before furnace operation.
4. Modification treatment When the temperature of the alloy liquid reaches 730-750°C, the total mass of the charge is 1.5%-2.5%
The three-way metamorphic agent is subjected to a modification treatment, and the metamorphic time is 15-18 minutes.
5. Pouring When the deterioration is completed, the residue is removed and stirred, and then allowed to stand for 5-10 minutes. When the temperature reaches
At 750°C, the slag is poured out.
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