Effects Of Zr On Solidification Behavior And Heat-treated Microstructure Of Al-3Fe Alloy

Al-Fe alloys have low density,high thermostability,rich in material and low price,which have high potential in the aerospace,weapons and automotive fields.However,large plate-like Al3Fe phase will be produced during normal solidification process,which splits Al matrix and severely reduces the mechanical property of the alloy.This limits the application of Al-Fe alloys.In order to optimize the microstructure of Al-Fe alloy,this paper investigates the solidification microstructure of Al-3Fe alloy solidified under crucible with insulation measures and iron mold with different mold temperature.The changes of microstructure and hardness of Al-3Fe alloys by iron mold casting with different Zr content were studied.Precipitation characteristics of Fe-rich phase and Zrcontaining phase under different aging conditions of Al-3Fe alloy with different Zr content were also investigated.The main conclusions are as follows:(1)The solidification microstructure of Al-3Fe alloy by slow cooling is primary Al3Fe+Al-Al6Fe eutectic.The solidification microstructure of Al-3Fe alloy by iron mold casting is Al-Al6Fe eutectic.With the increase of the mold temperature,the microstructures of the central parts of ingots have regular changes are as follows:transgranular structure,dendritic α-Al,dendritic and cell α-Al,equiaxed eutectic cell.(2)Branches of Al3Fe phase of Al-3Fe alloy are reduced with Zr addition by slow cooling.The morphology of Al3Fe changed from long needle to plate-like.Al-Al6Fe eutectic cells are refined with Zr addition by iron mold casting.However,plate-like Al3Fe formed in cell boundaries with Zr addition.Hardness of refinement cells is not obviously improved.(3)Al6Fe fibres begin to spheroidize during aging at 450℃.When the aging temperature is 500℃,spheroidization of A16Fe is more obvious.Moreover,rod-like Al3Fe formed in cell boundaries at the same aging condition.Zr addition can stabilize the Al6Fe fibres’ morphology.Metastable Al3Zr(L12)particles precipitate in Al matrix finely with 0.2%Zr addition during aging at 450℃ for 10h.The hardness of alloy is improved obviously.Increasing the aging temperature to 500℃,metastable Al3Zr(L12)particles have dissolved and some plate-like Zr-containing phases and needle-like Al3Fe phases have precipitated.The hardness of the alloy is decreased because of the change of microstructure.