Microstructure engineering during directed energy deposition of Al-0.5Sc-0.5Si using heated build platform

•Multilayered melt pool shape and size, including thermal cycle at different build platform temperatures, are presented.•Gradient microstructure is presented inside the melt pool from top to bottom for the varying cooling rate.•Innovative grain refinement engineering for different build platform temperatures is analyzed and validated for Al-0.5Sc-0.5Si alloy.•Microhardness is correlated with an increase in the fraction of equiaxed grains inside the melt pool for multilayer deposition.