Modelling the semisolid processing of metallic alloys

摘要: Semisolid processing of metallic alloys and composites utilises the thixotropic behaviour materials with non-dendritic microstructure in semisolid state. The family innovative manufacturing methods based on this has been developing over last 20 years or so originates from scientific work at MIT early 1970s. Here, a summary is given of: routes to spheroidal microstructures; types processing; advantages disadvantages these routes. Background rheology mathematical theories thixotropy are then covered as precursors main focus review transient alloy slurries computational modelling. Computational fluid dynamics (CFD) can be used predict die filling. However, some reported rheological data obtained steady state experiments, where material maintained particular shear rate for time. In reality, thixoforming, slurry undergoes sudden increase rest 100 s−1 more it enters die. This change takes place less than second. Hence, measuring response under rapid changes critical development modelling filling successful design industrial processing. The categorised one-phase two-phase finite difference element. Recent by Alexandrou coworkers and, separately Modigell coworkers, led production maps which, respectively summarise regions stable/unstable flow laminar/transient/turbulent fill. These great potential use prediction appropriate process parameters avoidance defects. A novel approach Rouff involves micro-modelling `active zone' around particles. There little quantitative discrepancies otherwise between fill simulations experimental results (usually through interrupted filling). no direct comparisons capabilities various software packages model geometries accurately. addition, depends sparse, particularly increasingly complex models. Direct visualisation provide useful insight avoid effects inertia experiments.