Fabrication and Characterization of Functionally Graded in-situ Al/Al-Cu-Cr Composite by Centrifugal Casting Process

The functional graded Al/Al-Cu-Cr composite was developed by horizontal centrifugal casting method and the effect of mold speed on the microstructure and hardness was investigated. The microstructure assessment and identification of the resulting phases was performed using X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) equipped with an Energy Dispersive X-Ray Spectroscopy (EDS). The results showed that ternary in-situ Al/Al-Cu-Cr composite microstructure was consisted of four phases α-Al, Al2Cu, θCr(Al7Cr) and ζ-Al-Cr-Cu. The centrifugal force caused the separation and movement of the intermetallic particles containing chromium (θCr(Al7Cr) and ζ-Al-Cr-Cu) toward the outer region of the composites with a decreasing trend to the middle region. The Al2Cu particles distributed toward the inner region of the specimens and were evenly distributed from the inner region to the middle region. As the mold rotation speed increased, the observed separation gradient increased so that the maximum area fraction of intermetallic particles in the outer region increased from 17% at 600 rpm to 36% at 1800 rpm. The results showed that the in-situ Al/Al-Cu-Cr composite has a higher hardness than the binary Al/Al-Cr composite at the same conditions. So that an increment of 80 percent in hardness was observed for the Al/Al-Cu-Cr composite compared to the Al/Al-Cr composite in their outermost region. As the rotational speed increased from 600 to 1800 rpm, the maximum amount of hardness which was associated with the outermost region of the centrifugally cast Al/Al-Cu-Cr composite increased from 51 to 76 Brinell.