Study Of Ultrasonic And Solute Effect On Internal Friction Of Casting Aluminum Alloys

Cast aluminum alloy has a series of advantages, such as good liquidity, good thermal conductivity, good processing performance, the casting cycle is short, good chemical stability, the ratio of strength to surface density is high. Therefore, it is widely used in various fields of manufacturing industry. Commonly used casting parts such as piston,rotating bracket,bearing, cylinder and so on. They can't fully meet the needs of production and life,because they produce huge vibration and serious noise.Through the existing process can improve these effects to a certain extent, they can not fundamentally solve the human needs of noise and reduce vibration. So how to improve the damping performance of the material, reduce vibration and noise, it had become a subject of inquiry. The internal friction technique is an effective means to study the microscopic mechanism of material and understand the microscopic characteristics of materials. It has important research significance and practical value for us in many respects. Such as study the internal structure of the material,understand the physical properties of the material, and how to improve the properties of materials to make it better to meet the needs of human beings.In this paper, we had added four kinds of solute elements(Cu, Mg, Zn, Cr)to molten aluminum. Casting under two conditions of ultrasonic vibration and non ultrasonic vibration. We had used different frequencies to test the performance of internal friction of four kinds of different aluminum alloy by internal friction apparatus. We had observed the size of grain by optical microscope. We had analyzed the content of elements in the crystal by scanning energy spectrum. We had made the necessary heat treatment for the material. Study the microscopic mechanism of different alloys, understand the characteristics of the internal friction peak and the generation principle, the change rule. We would explore the role of internal friction peak in alloy grain size, internal structure,,phase transition,,impurities and so on. The following main innovative conclusions have been obtained:(1)The addition of different solute elements can change the internal structure of aluminum alloy to a certain extent. We analyzed the information of the internal friction temperature curve, this information can reflect the micro mechanism of the alloy materials to some extent, such as the size of grain boundary, the existence of the precipitation phase, the existence of impurity elements, the content of impurityelements and so on.(2)Applying ultrasonic vibration and changing the content of solute elements can change the grain size of the alloy to a certain extent. It will have an impact on the grain boundary internal friction peak. The grain size of the alloy was smaller than that of the alloy which was not applied by ultrasound, the temperature and height of peak will be lower. Changing solute element content, when the grain size decreases, the temperature and height of boundary internal friction peak will be lower. On the contrary, it will be increase. If the solute elements in the alloy forming precipitation,phase transition peak will be produce in the alloy.(3)There were different internal friction peak in four kinds of aluminum alloy.There was one peak in the Al-Cu, it was phase transition peak.There were two peaks in the Al-Mg, they were boundary internal friction and phase transition peak which formed by supersaturated solution. There was a peak which caused by discontinuous precipitation in the Al-Zn. There were two peaks which were boundary internal friction peak and Snoek peak in the Al-Cr.(4)The principle of different peak is not the same. In Al-Mg, the phase transition peak which generated by over saturated phase, It forms an intermediate phase which was ?'above the recovery temperature. In Al-Zn, the phase transition peak which generated by discontinuous precipitation. It precipitates at the grain boundary and develops to the grain boundary. Grain boundary internal friction peak is caused by grain boundary sliding lag viscous in forced vibration and heating. In Al-Cr,Snoek peak is caused by increasing of the nonmetallic element such as carbon and oxygen in the alloy.