Microstructural development and mechanical properties of drop tube atomized Al-2.85 wt% Fe

Al-2.85 wt% Fe alloy has been subjected to non-equilibrium container-less solidification using a 6.5 m drop tube. Spherical samples were collected and sieved into 7 sizes fractions ranging from 850 μm to 53 μm, with the estimated cooling rates being 150 to 11000 K s-1 respectively. XRD analysis was employed on all droplet size fractions for identification and evolution of the phases, showing that Al, Al6Fe and Al13Fe4 were formed for all sizes while Al5Fe2 was observed only in droplets ≤ 150 μm in diameter. Microstructural evaluation was conducted by using SEM and optical microscopy, showing that droplet larger than 300 µm in diameter exhibited distinct morphologies; microcellular, dendritic α-Al with inter-dendritic Al13Fe4 eutectic and an Al-Al6Fe eutectic region. With increasing cooling rate, the Al-Al6Fe region disappears. EDX analysis reveals that increasing the cooling rate increased the dissolved Fe content in α-Al from 0.37 wt% Fe to 1.105 wt% Fe, and correspondingly the eutectic fraction decreased from 49.7 vol.% to 26.7 vol.%. Measurement of the lamellar spacing allowed the eutectic growth velocity and interfacial undercooling to be calculated, wherein the Al-rich boundary of the eutectic coupled zone could be reconstructed. This shows a coupled zone skewed significantly towards the intermetallic side of the eutectic. In order to understand the effect of non-equilibrium the solidification on the mechanical properties micro hardness of the droplets was measured. The micro-hardness has risen from 55.3 HV0.01 to 66.5 HV0.01 for ≥ 850 μm and ≤ 75 μm droplets, respectively.