Microstructure Examination and Sliding Wear Behavior of Al-15%Mg 2 Si-xGd In Situ Composites before and after Hot Extrusion

In current study; the effect of various Gadolinium (Gd) additions on the microstructure and sliding wear behaviour of Al-15%Mg 2 Si composite before and after the hot extrusion process was examined. Optical microscopy (OM), scanning electron microscopy (SEM) equipped with EDX facility and X-ray diffraction (XRD) were used to characterize the microstructure. The results showed that with addition of 1.0 wt.% Gd to Al-15%Mg 2 Si composite, the primary Mg 2 Si particles size reduced from 44 µm to 23 µm and its morphology altered from dendritic to polygonal shape. Further refinement of primary Mg 2 Si particles was achieved after conducting hot extrusion which resulted in a decrease in its size to 19 µm with a transfer to near-spherical morphology. The Vickers hardness value increased from 55.6 HV in the as-cast and unmodified composite to 72.9 HV in the extruded 1.0% Gd modified composite. The wear test results revealed that composites treated with Gd possess higher wear resistance in comparison with those of without Gd. The highest wear resistance obtained with the lowest wear rates of 0.19 mm 3 /km and 0.14 mm 3 /km in the Al-15%Mg 2 Si-1.0% Gd before and after the hot extrusion, respectively. The high wear resistance of extruded Gd-modified Al-15%Mg 2 Si composite is due to the refinement of primary Mg 2 Si particles with uniform distribution in the composite matrix along with fragmentation of Gd intermetallic compounds.