Rheological Behaviour and Microstructural Evolution of Semi-Solid A356 Alloy Produced by Different Routes
Different techniques used to produce semi-solid alloys can result in different structures in the material and, therefore, in distinct rheological behaviours which determine its thixo-forming ability. Suitable raw materials to be used for SSM forming must present non-dendritic, very fine or fragmented structure in order to globularize without excessive agglomeration when re-heated to the semi-solid state. This work analyses the influence of raw material production route on the rheological behaviour of semi-solid A356 alloy. Techniques used were: electromagnetic stirring (EMS) and chemical ultra-refining (UR). Samples were re-heated to 580oC (~ 0.45 solid fraction) and hold for 0, 90 and 210s to allow the observation of the structure evolution. After structures characterization, the samples were submitted to compression tests, at δH/δt = 10mm/s, in the same temperature/holding time conditions. Viscosity of the differently prepared raw material was related to the grain size, primary particle size, geometrical factor (roundness shape factor and contiguity).
C.G. Kang, S.K. Kim and S.Y. Lee
E. J. Zoqui et al., "Rheological Behaviour and Microstructural Evolution of Semi-Solid A356 Alloy Produced by Different Routes", Solid State Phenomena, Vols. 116-117, pp. 565-568, 2006