Influence of NbC addition in aluminium alloy A380 on microstructure at semi-solid processing temperature

Semi-solid processing is a promising technique used to fabricate parts, minimize manufacturing steps post preparation, and reduce casting defects. The globular structure is the key in this process, a characteristic achieved with the partial remelting of material to temperatures between solidus and liquids. In this sense, the aim of this research is to evaluate the microstructure quality of the aluminium matrix composite (AMC) reinforced with NbC, after semi-solid treatment. Micron-sized NbC powder with 0 wt. %, 5 wt. %, 10 wt. %, and 15 wt. % was employed as reinforcement, to fabricate a composite through the stir casting method. Furthermore, was used an Al-5Ti-1B alloy grain refinement. Globularization heat treatment at 562 °C, with a holding time of the 90s, was realized. An optical microscope under conventional and polarized light and a scanning electron microscope (SEM) allows the microstructure analyses. The dendritic cell size (DCS), grain size (GS), shape factor (SF), and rheo quality index (RQI) were used to analyse the morphology and microstructure. The results show a general reduction of GS and DCS parameters with a higher amount of NbC. The AMC with NbC shows more globular microstructure when compared with non-reinforced alloy.