Microstructure Characterization, Mechanical, and Tribological Properties of Slow-Cooled Sb-Treated Al-20Mg₂Si-Cu In Situ Composites

Role of Sb addition on structural characteristics, mechanical properties, and wear behavior of Al-20Mg₂Si-Cu in situ composite under slow cooling condition was thoroughly investigated in this study using stereomicroscopy, optical and scanning electron microscopy, thermal analysis, tensile, impact, hardness tests, and wear tester. Results show that addition of 0.8 wt.% Sb was found to produce a change in the morphology of primary Mg₂Si from dendrite to fine polygonal shape. At this Sb addition, the primary Mg₂Si phase also exhibited a reduction in size from 179.4 to 128.6 μm, an increase in density of Mg₂Si per area from 12.5 to 32.2 particle/mm², and a decrease in the aspect ratio from 1.24 to 1.11. Increasing the amount of Sb added up to 1 wt.% also resulted in a decrease in both nucleation and growth temperatures of the eutectic Mg₂Si by 2.6 and 1.7 °C respectively, which is most likely due to change of eutectic Mg₂Si morphology from flake to fibrous structure. Thermal analysis technique showed that distribution of Mg₂Si particles influences the heat conductivity during the solidification process of Al-Mg₂Si composite. The results also showed that improvements in mechanical properties of composite were obtained with increasing Sb content due to modification of both primary and eutectic Mg₂Si and due to intermetallic compound transformation from β-Al₅FeSi to α-Al₁₅(Fe,Mn)₃Si₂. Examination of fracture surfaces from tensile and impact samples showed that the base composite failed in a brittle manner with decohered or debonded Mg₂Si particles, whereas the 0.8 wt.% Sb-treated composite showed more cracked Mg₂Si and ductile fracture in the matrix. Wear properties improved significantly with addition of Sb due to modification and better dispersion of fine Mg₂Si particles in matrix.