Fabrication of spray-formed hypereutectic Al-25Si alloy and its deformation behavior

This article reports the fabrication of hypereutectic Al-25Si alloy, which is expected to be applied to the cylinder liner part of the engine block of an automobile due to its excellent wear resistance, low density and low thermal expansion coefficient, through a spray casting process and the characterization of the microstructural and the mechanical properties of this alloy. The OSPREY process used in this study is one of spray forming techniques, which can produce semi-finished products such as billet, tube, and plate with rapid solidification (RS) structure and density in a single operation from molten metal. The obtained microstructure of the hypereutectic Al-25Si alloy appeared to consist of Al matrix and equiaxed Si particles with average diameter of 5-7 mum. To characterize the deformation behavior of this alloy, a series of load relaxation and compression tests have been conducted at temperatures ranging from RT to 500 degreesC. The strain rate sensitivity parameter (m) of this alloy has been found to be very low (less than or equal to0.1) below 300 degreesC and reached maximum value of about 0.2 at 500 degreesC. During the deformation above 300 degreesC in compression, remarkable strain softening has been observed. The extrusion has been successfully conducted at the temperatures of 300 degreesC and above with the ratio of area reduction of 28 and 40 in this study. (C) 2002 Elsevier Science B.V. All rights reserved.