Effect of Heat Treatment on the Characterizations of Functionally Graded Al/Al2Cu Fabricated by Horizontal Centrifugal Casting

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 × 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 α-Al phase and consequently improve the hardness and CTE of the FG pipe.