The role of Ni and Fe aluminides on the elevated temperature strength of an AlSi12 alloy

The strength at room temperature and at 300 °C as well as the thermal cycling creep resistance are studied for an AlSi12Ni alloy and compared with Ni-free AlSi12 and AlSi1.1 alloys in as cast condition and after different spheroidization treatments. The architecture of the AlSi12Ni cast alloy consists of a ductile α-Al matrix and a rigid, long-range three-dimensional structure of eutectic Si and primary aluminides. In the as cast condition, the AlSi12Ni alloy shows ∼50% higher strength at 300 °C and ∼30% longer thermal cycling life as compared to the AlSi12 alloy. The strength and the thermal cycling creep resistance decrease for both the AlSi12 and AlSi12Ni alloys with increasing periods of the spheroidization treatment at 540 °C and stabilize at ∼24 h. The higher strength at 300 °C and the lower minimum strain rate in thermal cycling creep exhibited by the AlSi12Ni alloy with respect to the Ni-free alloys is conserved independently of the spheroidization treatment time. The improved thermomechanical properties exhibited by the AlSi12Ni alloy are due to the load carrying capacity of the hybrid three-dimensional structure. This is promoted by the preservation of the contiguity between the aluminides and the eutectic Si during ST as well as by the characteristics of the rigid phases such as mechanical properties, volume fraction, morphology and distribution.