Microstructure and Wear Behaviour of Ultrasonically Processed Al–MgAl₂O₄ In-Situ Composite

This work reports the effects of ultrasonic treatment on microstructure and abrasive wear properties of in-situ Al–MgAl₂O₄ composites synthesized using Al and 2 wt% Mg alloy with a 2 wt% SiO₂ oxide source. Microstructural analysis (SEM, EDAX, FESEM, TEM, and polarized optical microscopy) proved that after ultrasonic treatment of the melt, MgAl₂O₄ particle got fragmented and particle size decreased from micron to nano-size range. Grain size was reduced by 68%, and the overall homogeneity of microstructure increased. After ultrasonic treatment, hardness of composites increased by 42% due to reactively generated and well-disseminated hard MgAl₂O₄ particles. Wear studies showed that ultrasonic treatment affected the abrasive wear properties of composites. A comparison of abrasive wear behaviour of non-ultrasonically treated (non-UST) Al–MgAl₂O₄ and UST Al–MgAl₂O₄ composites was evaluated using pin-on-disk apparatus against SiC abrasives with varying load (10–20 N). With increasing load, lesser wear loss and a reduced coefficient of friction were witnessed in UST Al–MgAl₂O₄ composites as compared to non-UST Al–MgAl₂O₄ composites. SEM analysis showed that surface deterioration seen for UST Al–MgAl₂O₄ composites was less severe than non-UST Al–MgAl₂O₄ composites. Further assessment of wear mechanisms by microstructural characterizations of the worn-out surface, wear debris and abraded abrasive media has explained improved tribological properties of UST Al–MgAl₂O₄ composite over non-UST Al–MgAl₂O₄ composite.