Study On Microstructures And Properties Of Rapidly Solidified Al-Fe-Y/La Alloys

In this paper, cast ingots, sub-rapidly solidified bars and rapidly solidified ribbons of Al-5Fe,Al-5Fe-xY(x=0.6,1.6,3.0,5.0 wt.%)and Al-5Fe-yLa(y=0.5,1.0,1.5,3.0 wt.%)alloys were prepared by vacuum melting, vacuum suction casting and melt spinning ribbon. The different effects of cooling rate,rare earth elements and content on microstructure and properties of Al-Fe alloys, especially,the structure, phase composition and thermal stability of rapid solidified alloy were investigated by using optical microscopy (OM), X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimeter (DSC) and hardness tester, etc.It was found that the acicular Al3Fe phase transferred to spherical phase with the size of 20μm and flower-like phase with the size of 40μm, while 3.0wt% Y and 1.5wt% La were added in the as-cast Al-5Fe alloy respectively. And, microstructure of alloys can be refined. Results show that addition of Y and La can cause the constitution undercooling at forefront of solid liquid interface, reduce the misfit degree and interfacial energy between the A13Fe phase and the matrix, and refine the microstructure. Meanwhile, hardness tests result shows that the hardness of the alloy with addition of Y and La was increased to 130HV and 114HV respectively, while that of the as-cast alloy was only 81HV.Compared with the as-cast alloy, microstructure of the sub-rapid solidification alloy was apparently refined. With addition of 3.0wt%Y, spherical phase with the size of 5μm diameter was found in the alloy. While in the alloy with 1.5wt% La, the iron-rich phase was flower-shaped with diameter of 7μm. XRD analysis showed that metastable phase of Al6Fe and Al11La3 existed, while Y and La were added in the sub-rapid solidification Al-5Fe alloy respectively.The hardness was increased to 175HV and 140HV, significantly higher than that of the as-cast alloy. Therefore, the properties Al-Fe alloy can be improved effectively by increasing the cooling rate and adding appropriate amount rare earth elements.Through rapidly solidification, the most refined microstructure was gained. Dispersed secondary precipitations were also found, which were asserted to be A110Fe2Y and A110Fe2La phase by XRD and TEM. DSC curves indicated that at high temperature, phase transition temperature of rapidly solidified Al-5Fe alloy was respectively increased by 8℃and 5℃, with the addition of Y and La. It was obvious that rapid solidification increased the solubility of Fe, Y and La in the alloy, promoted the nucleation of intermetallic compounds, and inhibited the coarsening of the crystalline microstructure. Consequently, the thermal stability and mechanical properties of the alloy were improved.