Thixoforging of aluminum nano-composites synthesized by ultrasonic stir castin

Metal matrix composites reinforced with nanoparticles have shown great potential due to their excellent physical and mechanical properties. However incorporation of these composites in forming complex engineering parts is a great challenge. Thixoforging is an attractive technique where metal is deformed at a semi-solid temperature corresponding to higher solid fraction. Due to its inherited advantages like lesser forming load with increase in die life and reduction in forming steps, thixoforging is widely used in making complex parts of automobile and electronic industries mainly from aluminum alloys. Applying this technique to metal matrix composites provide additional advantages like improved mechanical behavior and better forming capabilities. The aim of this research is to develop aluminum based nanocomposite and subsequently thixoforged it to a required shape. In order to achieve this, aluminum alloy (A356) reinforced with SiC nanoparticles was stir casted using ultrasonic treatment as a feed stock material for thixoforging operation. The composite obtained after casting was uniformly heated using induction heating device and quickly transported to forging press for thixoforging operation at two different solid fraction of 60% and 50% using reheating holding time of 1 and 2 minutes. Different concentration of SiC was used to characterize the microstructure and mechanical properties of the composite. The microstructure characterization was carried out using optical micrograph, scanning electron microscopy (SEM) associated with energy dispersive x-ray analysis (EDX) and mechanical behavior was studied using hardness and tensile testing measurements. The results revealed that addition of SiC particles aided in refining the solidifying microstructure. Good distribution of reinforcement and better mechanical properties were observed in stir cast samples treated with 80W/cm2 ultrasonic intensity. The microstructure changed from non-dendritic rosette to near globular morphology after induction heating. Better reheating conditions were obtained with using intermediate power of induction with holding time of 2 minutes. The microstructure of thixoforged nanocomposite showed more SiC particles agglomerated away from the center of the thixoforged part. The hardness of the nanocomposite increased with increase in amount of SiC content. Increase in ductility of nanocomposite was observed after thixoforging operation. Thixoforging at solid fraction of 50% gave complete die filling, high densification, high hardness and better tensile results.