Materials Research Group
Permanent URI for this community
Browse
Browsing Materials Research Group by Author "Ajersch, F."
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Metadata only Deformation behavior of semi-solid A356 Al-Si alloy at low shear rates: The effect of sample size(Elsevier Science SA, 2007) Lashkari, O.; Ghomashchi, R.; Ajersch, F.The rheological behavior of semi-solid metal slurries at low shear rates can be characterized by parallel plate compression tests of cylindrical discs where the height (h) is much smaller than the diameter (d) and the axial flow is assumed negligible or zero against the radial flow. In order to confirm the validity of required aspect ratio, two sets of cylindrical test samples with (h/d) of 0.4, d = 24 mm small discs, and 1.8, d = 75 mm billets, were prepared with similar microstructures. The small specimens were tested in a parallel plate squeezing flow rheometer to determine the viscosities which were compared to the viscosity values of samples (billets) with larger aspect ratios using a similar large scale apparatus. For the billets, rheocast samples, it was shown that the dendritic primary α-Al structure has the highest viscosity. The viscosity decreases when the structure comprises a rosette or globular morphology. Similar results were obtained for the discs, thixocast samples, where the specimens have similar initial microstructure. The results confirmed that for low shear rates, less than 10-2 s-1, the viscosity of semi-solid alloy is dependent mainly on the morphology of the primary particles and not the sample size. © 2006.Item Metadata only Effect of fraction solid and shear rate on the viscosity of conventionally cast semi-solid A356 Al-Si alloys(2006) Lashkari, O.; Ghomashchi, R.; Charette, A.; Ajersch, F.; Aluminium 2006 (2006 : Montreal, Canada)Item Metadata only Microstructure and rheological behavior of grain refined and modified semi-solid A356 Al–Si slurries(Pergamon-Elsevier Science Ltd, 2006) Nafisi, S.; Lashkari, O.; Ghomashchi, R.; Ajersch, F.; Charette, A.A comprehensive study was carried out to establish the effect of melt treatment using Ti-B grain refiner and Sr modifier additions on the microstructural evolution and rheological properties of A356 aluminum alloy in the semisolid state. Rheocast billets of 75 mm in diameter and ∼140 mm in length, prepared by the SEED process, were deformed and several parameters were investigated to characterize the flow behavior of the billets in a compression test. Strain-time graphs were used to calculate the viscosity and liquid segregation was monitored to identify the optimum conditions for melt treatment. It is shown that non-treated alloy has the highest apparent viscosity. Refined semisolid billets have smaller particle size and more globularity of primary α-Al particles and as a result deform and flow more easily. It is postulated that modifier addition reduces the liquid surface tension and leads to improved deformability. © 2006 Acta Materialia Inc.