In-Situ Method for the Investigation of Equiaxed Grain Growth in Hypoeutectic and Hypereutectic Al-Si Alloys

Abstract

There are few experimental and kinetic studies of equiaxed-dendrite nucleation and growth in the mushy zone during the solidification of liquid metal alloys. Existing studies have either tried to deduce the solidification kinetics and mechanism from the final as-cast structure or to simulate the development of the grain structure using transparent organic solutions. These methods have short-comings in that they cannot account for various phenomena such as dendrite fragmentation, coarsening or grain refining. Pedneau et al have recently developed a method for the in-situ and real-time investigation of equiaxed-grain growth in the mushy zone during solidification (1). The method is based on the Electrical Sensing Zone (ESZ) technique, and allows for the monitoring of the density and size distribution of equiaxed grains in aluminum alloys during solidification. Electrical Sensing Zone (ESZ) principle has been the basis of various methods, such as the Coulter counter used to size particles in liquids. An application of ESZ in liquid metals is the Liquid Metal Cleanliness Analyzer (LiMCA)* which is an on-line technique for the analysis of non-metallic inclusions in liquid aluminum alloys. The LiMCA probe consists of two electrodes one of which is encased in a borosilicate tube which has an orifice. A constant current is maintained between the two electrodes. When the metal is drawn into the tube via a negative applied pressure, any non metallic particle passing through the orifice in the presence of the constant current causes a voltage change which is proportional to the volume of the particle through (2‐ 4), DR 5 4r d 3