Effects of mold temperature on the microstructure and tensile properties of SiCp/2024 Al-based composites fabricated via powder thixoforming

In this study, the effects of mold temperature on the microstructure and tensile properties of 2024 Al-based composites reinforced with SiC particles (SiCp; 10 vol.%) and fabricated via powder thixoforming were investigated. The tensile properties of the composite were dependent upon the mold temperature because it affected the secondary solidification behavior, compactness of the secondary solidified structures, dislocation density introduced by the plastic deformation that occurs during thixoforming, and recrystallization behavior. The tensile properties of the composite that was thixoformed at 350 degrees C exhibited the largest improvements, with the ultimate tensile strength (UTS) increasing by 235.4% (UTS = 379 MPa) and elongation decreasing by 31.0% (elongation = 4.0%) compared to those of the as-cast 2024 alloy. The increased UTS was ascribed to the thermal-mismatch and load-transfer strengthening mechanisms, enhanced compactness, increased dislocation density, decreased grain size, and lower concentration of the deleterious.-phase. The fracturing of the composites was caused by the cracking and debonding of the SiCp as the mold temperature increased, which in turn led to the total matrix failure. (C) 2016 Elsevier Ltd. All rights reserved.