Effect of tilted plate vibration on solidification and microstructural and mechanical properties of semisolid cast and heat-treated A356 Al alloy

摘要

A356 Al alloy melt solidified partially while flowing down a bottom cooled tilted plate. Columnar dendrites were formed on the plate wall. Because of forced convection, the dendrites were sheared off into equiaxed/fragmented grains and washed away by producing semisolid slurry at plate exit. Plate vibration enabled necessary shear for generating slurry which got solidified in metal mold to produce semisolid-cast billets of desired microstructure. Semisolid-cast billets were also heat treated to improve surface quality. The present investigation illustrates effect of plate vibration on solidification and microstructural and mechanical properties of semisolid-cast and heat-treated billets produced using tilted plate. This study involves five different plate vibrations (0, 15, 30, 40, and 50 Hz). Plate vibration of 30 Hz gave the finest and globular microstructure with superior mechanical properties. Because, little lower plate vibration slowed down dendrite fragmentation and grain refinement owing to inadequate shearing causing increase in grain size and decrease in shape factor, primary alpha-phase fraction, and grain density. Whereas, little higher plate vibration caused coarsening (which opposes grain refinement) due to coalescence/agglomeration and Ostwald ripening also resulting the same. Such variation in grain size with plate vibration caused variations in mechanical properties because of Hall-Petch effect. The results obtained are along the expected lines and in very good agreement with the results available in the literature.