Growth of intermetallic layer at roll bonded IF-steel/aluminum interface

The solid-state reactive diffusion between IF-steel and Al was experimentally studied using IF-steel/Al/IF-steel diffusion couples. The specimens were prepared by a roll bonding technique and then annealed at temperatures 773 K for different time span. At the IF-steel/Al interface in the annealed diffusion couple, wavy layer of Al5Fe2 was observed. The average thickness (Tavg) of Al5Fe2 layer monotonically increases with increasing annealing time (t) according to the equation Tavg = k(t)n, where t is time in second. Value of n = 0.5 indicates that interdiffusion through aluminide phase is the rate controlling step. During annealing, IF-steel matrix has undergone recrystallization. Microstructure and hardness measurement of IF-steel shows that recrystallization process completes within 30 min. Effective heat of formation theory has been applied to predict phase formation sequence during annealing of IF-steel/Al/IF-steel diffusion couples.