Spinel effect on the mechanical properties of metal matrix composite AA6061/(Al2O3)p

The effect of 22% Al2O3 particles addition on the 6061 aluminium cast alloy, has been evaluated. With the aim of achieving a suitable understanding about this effect, a comparative study of mechanical behaviour, at room temperature, of the reinforced and unreinforced AA6061 alloy was carried out. The results suggest a decohesion between matrix and reinforcement, that involves a loss of mechanical properties. A fractographic study carried out by scanning electron microscopy (SEM), reveals that the fracture of the reinforced material takes place in the matrix–Al2O3 particles interface. The fracture mechanism seems to be influenced by spinel presence surrounding the aluminium oxide particle surface. The spinel creation comes about during the cast process promoting the loss of adherence between the aluminium matrix phase and the reinforced particles. In spite of the spinel attendance, one can notice that the aluminium matrix composite AA6061/(Al2O3)p in the T6 condition, that is, submitted to age hardening treatment, suffers a remarkable mechanical behaviour improvement. Transmission electron microscopy and X-ray diffraction techniques have allowed the microstructural change study and the spinel role in the Al–Al2O3 interface.