Effect of Heat Treatment on the Characterizations of Functionally Graded Al/Al 2 Cu Fabricated by Horizontal Centrifugal
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Copyright Ó 2020 American Foundry Society https://doi.org/10.1007/s40962-019-00401-5
Abstract In the present paper, in situ centrifugal casting as an advanced material processing method is proposed to fabricate Al–26 wt% Cu–7wt% Si FG pipe with the density of 3.5 g/cm3 and with the wear resistance of 1.85064 9 10-16 m3/mN. The casting mould is preheated to approximately 200 °C to avoid chilling effects, segregation, porosity and compensation of the shrinkage of the alloy during the casting. Variations of the Al2Cu-based content are investigated by the field emission scanning electron microscopy (FESEM) in conjunction with image analyser software (MATLAB code). The microstructure results show that the Al2Cu content smoothly decreases from the outer layer containing 44.4 vol% to inner layer containing 37.8 vol% due to the difference in density of constituent phases and elements. The graded properties
such as Vickers hardness, coefficient of thermal expansion and mechanical properties of the present FG pipe are measured to show the significant dependence of the microstructure. It shows that Vickers hardness value gradually decreases from the outer with 331.3 HV to the inner with 141.0 HV. Furthermore, the heat treatment of the samples is conducted in boiling water (100 °C) for 4.5 h to promote the formations of new Al2Cu particles into the a-Al phase and consequently improve the hardness and CTE of the FG pipe.
Introduction
Essentially, all centrifugally cast alloys can be termed as ‘functionally gradient’ materials because of force field-induced segregation effects that would lead to a variation of properties across the wall thickness of the casting. As a matter of fact, centrifugal casting has been used to create coaxial sandwich metal structures by sequential pouring metals of progressively lower melting temperatures into rotating moulds.3
Functionally graded materials (FGMs) are one of the newly extended artificial substances made of two or more constituent phases selected as an alternative to multilayered and monolithic composites. In composites made of FGMs, the composition and/or microstructure varies continuously along the parts in order to be well suited to specific functional performance.1 FGMs offer great promises for components demanding high level of hardness and specific strength. These advanced materials are highly adopted to miscellaneous engineering applications such as aerospace industry, fusion reactor and pressure vessels.2
International Journal of Metalcasting
Keywords: FGM, hardness, mechanical properties, CTE, microstructure
The increased usage of FGMs in many industrial applications has thus stimulated significant interest in finding the most effective and economic manufacturing methods. The common methods known as the centrifugal casting proposed by Fukui4 are the best choice for fabrication of
particulate reinforced Al-based metal matrix FG pipe. According to Eqn. 1,5 the Al2Cu-based content is expected to have the lowest value in the inner layer due to the higher density of Al2Cu b
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