Effect of heat treatment for enhancing performance of Al–5Ti–1B master alloy on mechanical and hot tearing properties of Al–7Si–3Cu alloy

Abstract

Al–7Si–3Cu alloy is widely used in automobile industry due to good casting properties and high strength to weight ratio. These alloys are the replacement of steels components in cylindrical heads and pistons now a days. The mechanical properties of Al–7Si–3Cu alloy can be enhanced by addition of Al–5Ti–1B master alloy. Further improvement in mechanical properties can be achieved by ball milling, hot rolling and heat treatment process of Al–5Ti–1B master alloy. The present investigation revealed the effect of heat treatment on the Al–5Ti–1B master alloy. (1) on grain refining performance, (2) mechanical properties, and (3) on hot tearing propensity; of Al–7Si–3Cu alloy. Six samples of Al–7Si–3Cu alloy have been investigated, one using as cast Al–5Ti–1B master alloy and remaining with annealed master alloy at temperatures of 400, 500, 600, 700 and 800 °C respectively. The outcomes indicate that heat treatment of master alloy improves its grain refining efficiency up to 700 °C. This improvement in grain refinement is attributed to increased relative intensity of TiAl3 phase along with the formation of certain new phases, like (Al, Ti)B2 with an increase in heat treatment temperature, upto 700 °C. The results indicate that the hardness and tensile properties of the Al–7Si–3Cu alloy also increases with an increase in addition level of the master alloy. The SEM analysis of crack surface demonstrates that the primary cause of hot tearing is the presence of porosity and liquid folds at the final stage of solidification, Maximum grain refining efficiency of the alloy has been achieved at 0.040 wt% (Ti) addition of master alloy annealed at 700 °C for 8 h. At the similar addition level of the master alloy, hot tearing is completely wiped out in Al–7Si–3Cu alloy. However, past the heat treatment temperature of 700 °C, settling and agglomeration of TiAl3 and TiB2 phases have been observed prompting to the isolation of aluminide particles towards the lower side which further reduced the grain refining efficiency of the alloy.