Preparation and Structural Characterization of Rapidly Solidified Al-Cu Alloys

Rapidly solidified Al100-x-Cu-x alloys (x = 5, 10, 15, 25, 35 wt%) were prepared and analyzed. High cooling rate increased the Cu solubility in alpha-Al matrix. The influence of the cooling rate on Cu solubility extension in Al was experimentally simulated. Thus the pouring was performed in metallic die and by melt spinning-low pressure (MS-LP) technique. Melt processing by liquid quenching was performed using a self-designed melt spinning set-up which combined the cooling technology of a melt jet on the spinning disc with the principle of the mold feeding from low pressure casting technology. The thickness of the melt-spun ribbons was in the range of 30-70 mu m. The cooling rate provided by MS-LP was within 10(5)-10(6) K/s after the device calibration. The obtained alloys were characterized from structural, thermal and mechanical point of view. Optical microscopy and scanning electron microscopy were employed for the microstructural characterization which was followed by X-ray analysis. The thermal properties were evaluated by dilatometric and differential scanning calorimetric measurements. Vickers microhardness measurements were performed in the study. In the case of the hypereutectic alloy with 35 wt% Cu obtained by MS-LP method, the microhardness value increased by 45% compared to the same alloy obtained by gravity casting method. This was due to the extended solubility of the alloying element in the alpha-Al solid solution.