Influence of Melt Superheating Treatment on the Cast Structure of Al-Sn Alloys

In this article, the effect of melt superheating treatment (MST) for Al-Sn alloys has been studied. To determine the optimal superheat temperature, the authors measured the temperature dependences of the kinematic viscosity, electrical resistivity, density, and surface tension of Al-Sn melts with tin contents of 10, 20, 30, 40, and 50 wt %. According to the measurement results, temperature t* is determined for each Al-Sn alloy; upon heating to that point, the micro-inhomogeneous state is destroyed and the heterogeneous liquid-homogeneous liquid structural transition occurs. MST results in a decrease in melt viscosity. It is found that temperature t* rises with an increasing tin concentration in the Al-Sn melt. An increase in the tin content in the Al-Sn melt also leads to a decrease in the absolute values of the kinematic viscosity and surface tension, while the electrical resistivity and density increase accordingly. Thus, the MST mode for Al-Sn alloys was determined. The effect of MST of the Al-Sn 50 wt % melt on the microstructure and mechanical properties of the ingot is studied. It is necessary to determine the structural sensitivity to the degree of overheating of the melts and find a new strategy to improve the shaping ability of the two-phase structure of Al-Sn alloys. The results show that the method of resistivity and viscosity are more sensitive and effective for determining the temperature of the superheat of the melt (MST mode). In addition, the desired modified Al-Sn ingot structure can be formed under normal casting conditions; MST can contribute to the formation of a modified ingot structure by increasing the solidification time and decreasing the average solidification rate by reducing the melt viscosity after superheating.