Solutions to Common Casting Defects of 7E04 Aluminum Alloys

Abstract: In industry, aluminum alloy is a very widely used structural material, which has been used in many industries, especially in aerospace and machinery manufacturing. In the process of continuous development of science and technology, the speed of industrial development is getting faster and faster. Therefore, the demand for aluminum alloy welded structural parts is also increasing. It is very necessary to study the welding problem of aluminum alloys. The application range of aluminum alloy is very wide, and the welding technology has also been improved, which can better promote industrial production. When 7E04 aluminum alloy is casted, it is very difficult to form, and cracks and porosity often occur during use, resulting in many problems in the use of this material. 7E04 aluminum alloy has very serious defects when it is put into use. Therefore, different casting processes are analyzed in this article, which is very beneficial to improve the performance and optimize the casting process of aluminum alloys.
 
In recent years, there have been great achievements in China's economic construction, making many industries undergo great changes in the development process, especially in industrial production. In the process of continuous development of science and technology, the application range of high-impact aluminum alloys is constantly expanding. 7E04 aluminum alloy is a super hard aluminum alloy. This aluminum alloy has very good strength, and its comprehensive performance is very good. It is a very common structural material used in the development of the aerospace industry. However, there are many problems for 7E04 aluminum alloys during casting, which have a great impact on their performance. Analysis of the composition, casting defects and microstructure of 7E04 aluminum alloy can optimize the casting process and improve the process parameters.
 
1. Test materials and methods of 7E04 aluminum alloys 
The composition of 7E04 aluminum alloy was analyzed, and it was found that this kind of aluminum alloy contained a lot of metal elements; there were many kinds. The temperature was controlled at 720 degrees Celsius in the smelting process, and the smelting time was controlled at 1.5 hours, so that aluminum alloys with better performance can be obtained. When the aluminum alloy is smelted, it can be refined with a sodium free refining agent. After standing for 10 minutes, the slag is slagging off, and then poured into the crystallizer; it is casted through the wiper, so that the 7E04 aluminum alloy cast stick can be obtained.
 
The 7E04 aluminum alloy metal casting rods must be processed for subsequent operations. When they are processed, they should be placed at a temperature of 465 degrees Celsius for 10 hours, then homogenized, and then cooled down by the air-cooled method. During the homogenization treatment, the casting rods should be sampled horizontally, and then the samples should be ground. After polishing, an appropriate mix ratio should be adopted, which can better ensure the casting effect. In the pouring process, great attention should be paid to the use of preservatives, and ethanol should be used for cleaning; the surface should be blown with hot air. When the ZEISS-AXIO inverted material microscope is used to observe the sample, the structure and composition of the as-cast state should be well analyzed and studied, so that the causes of casting defects can be well analyzed. In the casting process, it is necessary to adjust the process parameters such as the melting temperature and the melting speed, and then carry out repeated tests, so that the optimal melting and casting process parameters can be determined. When the melting point of the test material is measured by the DSC method, the overburning temperature can also be determined, so that the casting quality of the 7E04 aluminum alloy can be better controlled.
 
When the casting temperature of 7E04 aluminum alloy is 479.9 degrees Celsius, the DSC curve will absorb heat. At the same time, at the low melting point, the eutectic will also begin to melt, and the matrix will start to melt at 627.2 degrees Celsius. Therefore, when pouring 7E04 aluminum alloys, the homogenization temperature should not exceed 479.9 degrees Celsius. At the same time, you'd better control it at 465 degrees Celsius, as shown in Figure 1.
 
2. Test results and analysis
Under conditions of different smelting processes, the microstructure of 7E04 aluminum alloy changes. When the smelting temperature is 720°C, the aluminum melt is not fully bonded due to the low temperatures, resulting in unstable bonding between grains. There are obvious loose holes in the as-cast structure of the material; meanwhile, some alloying elements are not completely dissolved in the aluminum melt due to the low temperature, resulting in a lot of undissolved alloy phases in the structure. As the melting temperature increases, the dispersed phase becomes more uniform and finer, and defects such as porosity and gas holes are significantly reduced. When the smelting time is 1.5 hours and the smelting temperature is 740±5℃, the dispersed phase and crystalline phase in the as-cast structure of the material are uniform and fine. When the smelting time is increased to 2 hours, a large amount of segregation occurs. From the picture, it can be found that there are a lot of porosity, gas holes and big phases in the structure. Through SEM observation and energy spectrum analysis, these relatively big phases are undissolved alloy phases. Therefore, it is necessary to increase the melting temperature and prolong the melting time to repeatedly test. At smelted temperatures of 730±5℃, 740±5℃, and 745±5℃, when the as-cast microstructures are different, with the increase of smelting temperature, the dispersed phase becomes more uniform and finer, and the defects such as porosity and gas holes are obviously reduced. When the melting temperature is 745±5℃, the structure is the most uniform and the defects are the least. At the smelting temperature of 745±5℃, when the smelting time is extended to 2h and 2.5h, the as-cast microstructure will change accordingly; the disperse phase is uniform and fine, and the defects such as porosity and gas holes are reduced. However, with the extending of the smelting time, the segregation of components inside the structure becomes more and more serious, and there will be a burning loss.
 
3. Conclusion
When 7E04 aluminum alloy is processed, it is very difficult to form. Therefore, it is necessary to analyze and study its casting process. By analyzing the casting process, the parameters of the casting process can be controlled, which can better improve the casting effect. Through experimental research, it is found that the overburning temperature of 7E04 aluminum alloy should be controlled at 479.9 degrees Celsius, and the smelting temperature should be controlled at 475 degrees Celsius. When casting, it is necessary to ensure that the structure of the cast rod is very uniform to avoid more defects. When casting 7E04 aluminum alloys, control the smelting time within a certain range to avoid burning damage and segregation. The analysis of the casting process of 7E04 aluminum alloy can improve its casting parameters, which not only can improve its performance, but also promote better results in industrial production.