Structure and properties of nanostructured A357 alloy produced by melt spinning compared with direct chill ingot

The properties of nanostructured A357 ribbons produced by melt spinning were investigated using field emission gun scanning electron microscope, X-ray diffraction pattern, differential scanning calorimetry and microhardness testing in comparison with those fabricated by direct-chill (DC) casting. The solidification time and cooling rate of 46 mu m thick melt-spun ribbon were estimated to be 9.13 x 10(-6) s and 1.17 x 10(7) K s(-1), respectively. The results show that the nanostructure of A357 ribbons exhibits the enhanced solid-solubility of Si in Al matrix to 2.00 wt.% and the existence of ultra-fine and homogenous dendritic structure having a dendrite arm spacing of about 200 nm. The nano-sized spherical eutectic Si crystals having a size of 50 nm were also observed. All these structural factors increase the microhardness of the ribbon which is twice as high as that of DC casting. (C) 2011 Elsevier B. V. All rights reserved.