Microstructure of friction stir processed as-cast Al-Fe alloy

Al-3%Fe(mass fraction) binary alloy was prepared by fusion casting.The effect of reciprocating multi-pass friction stir processing(FSP) on the microstructure of the alloy was studied.The results show that the microstructure of each pass in stir zone is non-uniform after one to three passes reciprocating FSP.With the increase of processing passes,the degree of uniformity and refinement of the microstructure increases.The as-cast alloy is composed of the α-Al and coarse needle Al3Fe phases.The microstructure in stir zone is significantly refined after three passes FSP.The as-cast microstructure in the stir zone is changed into fine equiaxed recrystallized grains with the size of 2-5 μm,and stacking fault appears in some grains.Coarse needle Al3Fe phases are broken into granular phases with the length of less than 1 μm,and disperse in Al matrix grain boundary and grain interior.Refined Al3Fe particles present twin structure.