Abstract:The microstructure formation and strengthening of an Al-5wt.%TiO₂ composites with additions of 5 wt.% Cu and 2 wt.% stearic acid (as a process control agent, PCA) during mechanical alloying and subsequent thermal exposure were studied. The powder composites were prepared by high-energy ball milling for up to 10 h. Single line tracks of the powders were laser melted. Optical and scanning electron microscopy, XRD analysis and differential scanning calorimetry were used to study microstructural evolution. The results showed that the Cu addition promotes an effective mechanical alloying of aluminum with TiO₂ from the start of milling, resulting in higher microhardness (up to HV 290), while the PCA, on the contrary, postpones this process. In both cases, the composite granules with uniform distribution of TiO₂ particles were formed. Subsequent heating of mechanically alloyed materials causes the activation of an exothermic reaction of TiO₂ reduction with aluminum, the start temperature of which, in the case of Cu addition, shifts to lower values, that is, the transformation begins in the solid state. Besides, the Cu-added material after laser melting demonstrates a more dispersed and uniform structure which positively affects its microhardness.

Key words: mechanical alloying; Al-Ti-O system; aluminum matrix composites; microstructure; hardening; laser melting