Microstructural evolution and thixoformability of semi-solid aluminum 319s alloy during re-melting

• Published in: Journal of alloys and compounds Vol. 649; pp. 204 - 210
• Main Authors: Hu, X.G., Zhu, Q., Lu, H.X., Zhang, F., Li, D.Q., Midson, S.P.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-11-2015
• Subjects: 319s alloy; Coarsening rate; Confocal; Evolution; Heating rate; In-situ observation; Liquids; Melting; Microstructure; Semi-solid; Semi-solid processing; Thixoformability; Windows (intervals); Thixoformability; Semi-solid; 319s alloy; In-situ observation; Heating rate; Coarsening rate
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2015.07.121

The aim of this paper is to characterize both microstructural evolution and thixoformability during partial melting of semi-solid 319s alloy. The thixoformability criteria of 319s was initially investigated by thermodynamic analysis. In-situ observation of partial re-melting was performed by a Confocal Laser Scanning Microscope to determine the effect of heating rate on melting characteristics. Meanwhile, the microstructural evolution of 319s alloy at extremely low heating rate was also investigated in order to understand the mechanism of re-melting process. The studies demonstrated that 319s alloy is suitable for thixocasting because of the controllable liquid fraction in the operating window of 15 °C. The process window was effected by both temperature and heating time. The primary particles evolution in 319s alloy can be divided into four stages, and the coarsening rate during isothermal test is 227 μm3/s. The effective method to obtain desirable microstructure is to manage the time in the semi-solid state by controlling heating rate and soaking time.
•The thixoformability of 319s is discussed by using SPSC and thermodynamic analysis.•The re-melting processes at different heating rate are in-situ observed.•We identified the four stages of microstructural evolution during re-melting.•The coarsening rate K for 319s during isothermal test is identified.•The variation tendency of Si particle size with increasing time is reported.