Ordered stacking faults within nanosized silicon precipitates in aluminum alloy

A considerable amount of superfine Si precipitates with the sizes ranging from 5 to 15 nm were found uniformly dispersed in the Al matrix of an Al-1Si (wt.%) alloy after electropulsing treatment. Through high resolution transmission electron microscopy (HRTEM), an unusual 9R (ABCBCACAB…) ordered stacking faults were identified within the Si precipitates with a truncated tetrahedral morphology that hold a (1 1 1)_Si//(1 1 1)_Al & [101‾]_Si//[11‾0]_Al orientation relationship with the Al matrix. An atomistic model was established to preform image simulations and explain that the existence of these nanosized Si precipitates is attributable to increment of coincidence lattice sites between Si and Al.