Microstructural features and mechanical properties of spray -formed hypereutectic Al-Si-Ti alloy

Abstract

ABSTRACT In the present study, the effect of the addition of Ti on the microstructural and mechanical properties of hypereutectic (Al/15 wt. %Si) spray-formed (SF) alloys has been investigated and compared with as-cast (AC) alloys. Al/15Si and Al/15Si/2Ti alloys were synthesised by spray forming method. The microstructural features of the alloys were explored under an optical microscope, and a scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis were carried out for phase identification. The phase analysis confirmed the presence of α-Al and Si phases in all the alloys, with additional peaks attributed to Al3Ti and AlSi2Ti present in the Al/15Si/2Ti alloys. The microstructure of the SF1 alloy (Al/15Si) consisted of globular, fine Si phases (primary and eutectic) distributed homogeneously in the equiaxed Al matrix. The addition of Ti to the binary SF1 alloy led to the formation of an SF2 alloy (Al/15Si/2Ti) with a fine intermetallic phase of Al3Ti and further spheroidisation of Si particles. The SF1 and SF2 alloys exhibited 30% and 40% greater microhardness, respectively, than did their corresponding AC alloys. With the addition of Ti, the ultimate tensile strength of the SF2 alloy increased by 19% compared to that of the SF1 alloy. Furthermore, a significant increase in yield strength and ductility was observed in the SF alloys compared to the AC alloys. Adding Ti to hypereutectic Al/15Si alloy via the spray-forming method provides a better alternative material for aerospace and automotive applications.