Hardness and microstructural characteristics of rapidly solidified Al-8-16 wt.%Si alloys

Al-Si alloys with nominal composition of Al-8 wt. %Si, Al-12wt.%Si, and Al-16wt.%Si were rapidly solidified by using melt-spinning technique to examine the influence of the cooling rate/conditions on microstructure and mechanical properties. The microstructures of the rapidly solidified ribbons and ingot samples were investigated by the optical microscopy, electron microscopy and X-ray diffraction (XRD) techniques. The results showed that the structures of all melt-spun ribbons were completely composed of finely dispersed alpha-Al and eutectic Si phase, and primary silicon was not observed. The XRD analysis indicated that the solubility of Si in the alpha-Al matrix was greatly increased with rapid solidification. Additionally, mechanical properties of both conventionally cast (ingot) and melt-spun ribbons were examined by using Vickers indenter for one applied load (0.098 N). The hardness values of the melt-spun ribbons were about three times higher than those of ingot counterparts. The high hardness of the rapidly solidified state can be attributed to the supersaturated solid solutions. Besides, hardness values with different applied loads were measured for melt-spun ribbons. The results indicated that Vickers hardness values (H(v)) of the ribbons depended on the applied load. Applying the concept of Hays-Kendall, the load independent hardness values were calculated as 694.0, 982.8 and 1186.8 MN/m(2) for Al-8 wt.%Si, Al-12wt.%Si and Al-16 wt.%Si, respectively. (C) 2004 Elsevier B.V. All rights reserved.