Core-Shell-Structured Particle Reinforced A356 Matrix Composite Prepared by Powder-Thixoforming: Effect of Reheating Temperature

Tijun Chen,Min Gao,Libo Geng,He Qin

doi:10.3390/ma11091718

Abstract

A novel core-shell-structured Ti-(Al-Si-Ti) particle (Ti-(Al-Si-Ti)p) reinforced A356 matrix composite was fabricated by a new method, powder thixoforming, which combines the merits of both powder metallurgy and semisolid thixoforming. The effects of reheating temperature on the microstructure and tensile properties of the resulting composite were investigated. The results indicated that the thickening of the Al-Si-Ti compound shells, with rising the reheating temperature, significantly enhanced the strengthening role, but the fracture and peeling of the shells, at higher than 600 °C, impaired the strengthening effect. The composite formed at 600 °C had a favorable tensile elongation of 8.3% besides high tensile strengths. During tensile testing, the Ti@(Al-Si-Ti)p frequently fractured across the Ti cores and occasionally cracked around the Ti cores, but preferentially fractured between the outer cracked shells and the inner cores for the composites thixoformed at higher than 600 °C. The delayed formation of cracks in the Ti-(Al-Si-Ti)p and the small size of the cracks contributed to ductility improvement. The MSL model, modified according to the Ti@(Al-Si-Ti)p characteristics, was essentially suitable for predicting the yield strength of such composites. The largest contribution to the strength was resulted from solid solution strengthening of Ti element, but the strengthening role from geometrically necessary dislocations was significantly improved as the reheating temperature rose from 590 °C to 600 °C.

Highlights

Particle reinforced Al matrix composites (PRAMCs) have large application potential in the fields of aerospace, weapon, automobile and other high-end equipment because of their high specific strength and stiffness [1]
The Ti@(Al-Si-Ti)p distribute in the regions between the primary particles, i.e., in the 3Ss, and their distribution is quite uniform at the reheating temperatures of 590 ◦ C and 600 ◦ C (Figure 1a,b)
The primary particles at 590 ◦ C are in a form of interconnected small particles (Figure 1a), and are separated by the 3Ss accompanied with their growth, evolving into the individual spheroidal particles with an average size of about 55 μm at 600 ◦ C (Figure 1b)

Summary

Introduction

Particle reinforced Al matrix composites (PRAMCs) have large application potential in the fields of aerospace, weapon, automobile and other high-end equipment because of their high specific strength and stiffness [1]. The mechanical properties of the resulting PRAMCs are always relatively low due to weak interfacial bonding strength resulting from poor interfacial wettability and possible interfacial reaction [2]. Al3Ti particles (Al3Tip) have low density (3.4 g/cm3), high melting point (1340 ◦ C), high Young’s modulus (216 GPa), and equivalent coefficient of thermal expansion (CTE) to Al matrix alloys, so they are considered one of the most promising in situ reinforcements for Al matrix composites [1,5,6]. The Al3 Tip /Al matrix composites, similar to other ceramic particle reinforced Al matrix composites, always have very poor elongation, they possibly have high tensile strength [3,4,5]

Methods

Results

Conclusion