Effect of Thixoforming Process and Microstructural Changes in the A380 Matrix Composite Reinforced with NbC by the Stir Casting Method

Semisolid metal processing is a promising technique for obtaining complex low-porosity shapes. However, a number of researchers also use thixoforming for composites. This paper evaluates the thixoforming process in an aluminum matrix composite made by the stir casting process. The A380 aluminum alloy was reinforced with 4 different concentrations of NbC (0 wt.%, 5 wt.%, 10 wt.%, and 15 wt.%) by means of the stir casting method at 750°C. To obtain a non-dendritic feedstock, Al-5Ti-1B was added to the molten metal to achieve chemical grain refinement. Isothermal holding for 90 s was applied at the mushy stage of 60% solid fraction at 562°C, determined by differential scanning calorimetry analysis. Optical micrographs, scanning electron microscopy, and x-ray diffraction were used to characterize the material. After performing the thixoforming, an increase in hardness was observed under all conditions. The results show a globular-based morphology with fragmentation of the β-Fe intermetallic phase. The distribution of the NbC particles was improved after the thixoforming process. Thus, the stir casting technique, in conjunction with thixoforming processing of the composite material, A380 + NbC, is an efficient technological route for the manufacture of parts with good characteristics and properties.