Cast aluminum is a process method of forming the required shape aluminum parts by pouring it into the mold in a molten state. The aluminum used in cast aluminum is called cast aluminum alloy.Get a Quote
Aluminum Die Casting
Cast aluminum is a process method of forming the required shape aluminum parts by pouring it into the mold in a molten state. The aluminum used in cast aluminum is called cast aluminum alloy.
Is a pure aluminum or aluminum alloy ingot according to the standard proportion of ingredients, after artificial heating to turn it into aluminum alloy liquid or melting state, and then through a professional mold or the corresponding process of aluminum liquid or melting state of aluminum alloy pouring cavity, cooled to form the required shape of aluminum parts of a process.
The aluminum used in cast aluminum is called: cast aluminum alloy. Commonly used methods of cast aluminum are: sand casting, die casting, low-pressure casting, precision casting, permanent casting and so on.
Pay attention to the main points
First, the defect characteristics of oxidation slag: oxidation slag is distributed in the upper surface of the casting, in the casting does not ventilate the corner. Breaks are mostly gray-white or yellow, x-rayed or mechanically found, or in alkali washing, acid washing or anodization.
Cause: 1. Furnace material is not clean, return furnace material use is too much. 2. The pouring system is poorly designed. 3. The slag in the alloy fluid has not been removed. 4. The pouring operation is not correct and is brought into the slag. 5. There is not enough time to settle after refining the deterioration treatment. Prevention method: 1. Furnace material should be blown sand, the use of return furnace material should be appropriately reduced. 2. Improve the design of the pouring system and improve its slag-blocking capacity 3. Slag with an appropriate melt 4 Pouring should be smooth and should focus on slag 5 The alloy fluid should be lying for a certain period of time before pouring after refining.
Second, pores, defect characteristics: three casting wall gas holes are generally round or oval, with a smooth surface, generally bright oxidation skin, sometimes oily yellow. Surface pores, bubbles can be found through blasting, internal pores, bubbles can be found through X-ray or machining, bubbles on the X-ray negative black.
Cause: 1. The pouring alloy is uneven and involves gas. 2. Organic impurities (e.g. coal chips, grassroots horse manure, etc.) are mixed into the sand. 3. Poor casting and core ventilation. 4. The surface of the cold iron has shrink holes. 5. The pouring system is poorly designed. Prevention method: 1. Properly grasp the pouring speed and avoid getting involved in the gas. 2. Organic impurities must not be mixed into the type ( core ) sand to reduce the amount of air in the moulding material. 3. Improves the exhaust capacity of the ( core ) sand. 4. Proper selection and handling of cold iron. 5. Improve the design of the pouring system.
Third, shrink defect characteristics: aluminum castings shrink generally produced around the inner watering channel fly out of the root of the thick part, the wall of the thick thin transfer and with a large plane of the thin wall. In the casting state, the break is gray, the light yellow is heat treated for gray white light yellow or gray black on the x-ray negative is cloud-like serious silky shrinkage can be found by X-ray, fluorescence low-fold break and other inspection methods.
Cause: 1. The role of the vent replenishment is poor. 2. The furnace contains too much gas. 3. Overheating around the inner runner 4. The mould moisture is too high and the core is not dry. 5. Alloy grains are large. 6. The casting is not in the correct position in the mould. 7. The pouring temperature is too high and the pouring speed is too fast. Prevention method: 1. Rehydrate the metal solution from the outlet and improve the outlet design. 2. Furnace material should be clean and non-corrosive. 3. The casting is loosened to set the vent, and the cold iron or cold iron is placed in conjunction with the vent. 4. Control sand moisture, and core drying. 5. Take measures to refine the grain. 6. Improve the position of the casting in the mould to reduce pouring temperature and pouring speed.
Four, crack defect characteristics: 1. Casting cracks. Along the development of the crystal boundary, often accompanied by partial analysis, is a crack formed at a higher temperature in the volume of larger shrinkage of the alloy and the shape of the more complex castings easily appear 2 Heat treatment cracks: Due to heat treatment caused by excessive burning or overheating, often through the crystal crack. Often in the production of stress and thermal expansion coefficient of large alloy cooling drama. or when there are other metallurgical defects.
Cause:1. Casting structure design is unreasonable, there are sharp corners, the wall of the thick and thin changes are too wide. 2. The mould ( core ) is not regressive. 3. Cast local overheating. 4. The pouring temperature is too high. 5. The casting is removed prematurely from the mold. 6. Heat treatment overheats or overburns, cooling speed is too intense. Prevention method: 1. Improve casting structure design, avoid sharp corners, wall thickness for uniform, smooth transition. 2. Take measures to increase the mould ( core ) regression. 3. To ensure that each part of the casting solidifies or freezes sequentially at the same time, and improves the design of the pouring system. 4. Reduce the pouring temperature appropriately. 5. Controls the time when the mould cools out. 6. The casting is deformed by thermal correction. 7. Properly control the heat treatment temperature and reduce quenching cooling speed.
(1) When melting with aluminum ingots and intermediate alloys, first load the aluminum and then add the intermediate alloy.
(2) When smelting with prefabricated alloy ingots, first load the prefabricated alloy ingots and then add the required quantities of aluminum and intermediate alloys. When the furnace material consists of the furnace material and aluminum ingots, the largest part of the furnace material is first melted.
(4) When the furnace has sufficient capacity to load several furnaces at the same time, it should first be loaded together with ingredients similar to the melting point.
(5) Furnaces that are prone to burn and low melting points, such as magnesium and zinc, should be added at the end.
(6) In the case of continuous melting, a portion of the aluminum liquid shall remain in the crucible to accelerate the melting of the next furnace.
(7) When covering the melt, the melt should be added when the furnace material starts to melt. 
When smelting, the order and method of loading furnace material not only relate to the time of smelting, the burning loss of metal, heat consumption, but also affect the quality of metal melt and furnace life. The loading principles are:
1, the order of loading furnace material should be reasonable. The correct loading depends on the nature and state of the added furnace material, taking into account the fastest melting speed, minimal burn loss and accurate chemical composition control.
When loading, first small or thin pieces of waste, aluminum ingots and large pieces of material in the middle, and finally installed intermediate alloy. The melting point is easily oxidized by the intermediate alloy in the lower and middle layers. The loaded furnace material should be evenly distributed in the melting pool to prevent heavyness.
Small or sheet material is mounted on the lower layer of the melting pool, which reduces burn damage while also protecting the furnace body from direct impact from large pieces of material. Intermediate alloys have high melting points, such as AL-NI and AL-MN alloys with a melting point of 750-800degrees C,mounted on the upper layer, due to the high upper temperature in the furnace easy to melt, but also a full time to spread;
Furnace material is leveled, melting speed is similar to this to prevent heavy when caused by local metal overheating.
Furnace material should be once into the furnace, two or more feeding will increase non-metallic inclusions and gas content.
2, for high quality requirements of the product (including forgings, mold forgings, hollow girders and beam profiles, etc.) furnace material in addition to the above loading requirements, before loading must be sprinkled into the melting pool 20-30 kg powder melt, in the furnace process to layer the furnace powder melt, which can improve the purity of the furnace body, but also reduce losses.
3, electric furnace loading, should pay attention to the furnace material maximum point from the resistance wire distance must not be less than 100mm,otherwise easy to cause short circuit.
Once the furnace is finished, it heats up. Melting is the process of converting from solid to liquid. The quality of this process has a decisive impact on product quality.
As the furnace temperature increases during melting, especially when the furnace material starts to melt, the oxide film covered by the metal outer surface can easily rupture and gradually lose its protective effect. The gas is easy to invade at this time, causing further oxidation of the internal metal. And the melted liquid or flow of liquid to the bottom of the furnace, when droplets or fluid flow into the bottom of the pool, its surface of the oxide film will be mixed into the melt. Therefore, in order to prevent further oxidation of the metal and reduce the oxide film into the melt, when the furnace material softens and collapses, it should be appropriate to the metal surface sprinkled with a layer of powdered melt cover, the amount of which can be seen in the table. This also reduces metal inhalation during melting.
When the furnace material melts part, zinc ingots or copper plates can be evenly added to the liquid, so that the melt in the melting pool just can drown zinc ingots and copper plates.
It should be emphasized that the melting point of the copper plate is 1083degrees C,and that copper is dissolved in thealuminum alloy melt within the melting temperature range of the aluminum alloy. Therefore, if the copper plate is added too early, the melt can not cover it, which will increase the burning damage of the copper plate, and if it is added too late, the copper plate too late to dissolve and diffuse, will extend the melting time, affecting the chemical composition control of the alloy.
When smelting an electric furnace, try to avoid replacing the resistance ribbon to prevent dirt from falling into the melt and contaminating the metal.
C,stir the melt
Care should be taken during the melting process to prevent the melt from overheating, especially when the furnace temperature is as high as 1200degrees Cwhen the natural gas furnace (or gas furnace) issmelting, which is prone to local overheating at such a high temperature. For this reason, when the furnace material melts, the melt should be properly stirred so that the temperature of the melting pool is uniform, but also conducive to accelerating melting.
Pickle and stir
When the furnace material has been fully melted in the melting pool, and the melt temperature reaches the melting temperature, that is, a large amount of oxidizing slag floating on the surface of the melt can be removed.
Before slag should first evenly sprinkle powdered melt on the melt, so that slag and metal separation, conducive to pickpocketing, can bring out less metal. Slag requires smoothness to prevent slag from getting involved in the melting body. Slag to be thorough, because the presence of slag will increase the gas content of the melt, and soil the metal.
B,magnesium plus radon
After slag, magnesium ingots can be added to the melt body and covered with Powder 2 to prevent magnesium from burning. In order to prevent the poisoning of radon, wear a mask when adding radon. In addition, the slag that pickles after addition should be piled up in a special stacking site or specially treated.
Before sampling, after adjusting the chemical composition, stirring should be carried out in time. The aim is to make the alloy composition evenly distributed and the temperature in the melting body consistent. This may seem like an extremely simple operation, but it is an important process in the process. Because, some of the denser alloy elements easily sink, and the addition of alloy elements can not be absolutely uniform, which results in the melt between the upper and lower layers, the furnace between the regions of the alloy elements are unevenly distributed. If the stirring is not thorough (there is no guarantee of long enough time and the elimination of dead corners), it is easy to cause the chemical composition of the melt uneven.
Stirring should be carried out smoothly and should not stir too many waves to prevent the oxide film from getting involved in the melt.
Adjust the ingredients
During smelting, the alloy composition may change for a variety of reasons, which may cause the real composition of the melt to deviate significantly from the value of the ingredient calculation. Therefore, after the furnace melts, the sampling needs to be quickly analyzed in order to adjust the composition according to the analysis results.
After the melt has been fully stirred, samples should be taken for rapid pre-furnace analysis to analyze whether the chemical composition meets the standard requirements. The furnace melt temperature at the time of sampling shall not be lower than the melting temperature limit.
The sampling part of the quick analysis specimen should be representative, the open gas furnace (or gas furnace) takes a set of specimens at the center of the two furnace doors, and the electric furnace takes two sets of specimens at the center of the half melt. Sample spoon before sampling to be warmed up, for high-purity aluminum and aluminum alloy, this prevents sample spoon pollution, sampling should be made of stainless steel sample spoon and coated with paint.
When the results of the quick analysis do not match the alloy composition requirements, the composition should be adjusted - diluted or replenished.
First, replenishment. The quick analysis results are less than the alloy chemical composition requirements when the need for rehydration. In order for the feed to be accurate, it should be calculated according to the following principles:
1, first calculate the amount of less and then calculate more;
2, first count impurities and then alloy elements;
3, first calculate the middle alloy of low components, and then calculate the intermediate alloy of high components;
4, the final count of new metals
Rapid analysis results are higher than the national standards for chemical composition, delivery standards, etc. when the upper limit needs to be diluted.
Alloy elements above the chemical composition standard at the time of dilution should be flushed to the upper limit of the alloy element content below the standard requirements.
According to the production practice of aluminum processing plant in China over the years, the standards of aluminum alloys have been formulated in order to obtain good casting and mechanic properties of these alloys. For this reason, when diluted, the chemical composition required to approach or fall below the standard upper limit of the chemical composition in the plant of the element is generally flushed.
C, adjust the composition should pay attention to the matter
1, sample with meta-representative. The unpretentious samples are added, some elements have a high density, slow dissolving diffusion speed, or are easy to partial layering. Therefore, before sampling should be fully stirred to uniform its composition, due to the high surface temperature of the reflective furnace melting pool, low temperature of the furnace bottom, no heat effect on the spread, sampling before many times stirring, each stirring time must not be less than 5min.
2, sampling site and operation methods should be reasonable. Due to the large and deep melting pool of the reflective furnace, although many stirrings are made before sampling, the composition of each part of the melting pool still has a certain deviation, therefore, the specimen should be taken out at one-half of the deepest part of the middle of the melting pool.
Samples should be fully heated and dry before sampling, sampling when the operation method is correct, so that the specimen meets the requirements, otherwise the specimen has pores, slag or does not meet the requirements, will bring some error to the rapid analysis.
3, sampling temperature should be appropriate. For some dense elements, the dissolving diffusion speed increases with the temperature. If the melt temperature is low before sampling, although after many stirring, its dissolution diffusion speed is still very slow, at this time the sample taken out is still unrepresentative, so the sample should be controlled before the melt temperature is appropriately higher.
4, filling and dilution are generally used with intermediate alloys, melting point is higher and more difficult to melt new metal materials, should be avoided.
5, the amount of replenishment and dilution in the premise of ensuring alloy elements should be less and better. And when diluting should consider the capacity of the furnace and whether it is easy to dilute the relevant operation.
6, if the dilution is large, should also be filled with other alloy elements, should make the content of these alloy elements not less than the corresponding standards or requirements.
The vast majority of industrially produced aluminum alloys no longer have gas refining steel process in smelting furnaces, but mainly rely on static furnace refining and on-line melt purification treatment, some aluminum processing plants still have smelting furnaces, the purpose of which is to improve the purity of the melt. These refining methods can be divided into two categories: gas refining and melt refining.
When the melt is refined and the surface slag is removed, the metal melt can be infused into the static furnace for casting when the temperature is right.
Clear the oven
The furnace is to completely clear the remaining slag from the furnace. Whenever the metal comes out, a furnace is carried out. When the alloy conversion, ordinary products continuous production 5-15 furnaces, special products for each production of a furnace, generally to carry out a large furnace. When clearing the furnace, a layer of powdered melt should be poured evenly into the furnace, and the furnace temperature should rise above 800degrees C, and then a triangular shovel should be used to completely remove the remaining slag from all parts of the furnace. 
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