Effect of growth velocities on microstructure and mechanical properties of eutectic Al-Si-Mg-Ni-(Fe) alloy

In this study, the effect of microstructure on the hardness and tensile-strength properties of Al-Si-Ni- Mg quaternary eutectic alloy system at different growth velocities were investigated. The composition of Al-Si-Ni-Mg quaternary eutectic alloy system was chosen to be Al-13 wt%Si-3.5 wt%Mg-2 wt% Ni. The chemical composition of the alloys was determined by using XRF (x-ray fluorescence). Al-Si- Ni-Mg quaternary eutectic alloy system was directionally solidified at different growth velocities, 8.3 to 166.6 mu m.s(-1) by using a Bridgman-type furnace. The eutectic temperature of the quantitative alloy is 552.13 degrees C measured by DTA (Differential Thermal Analysis). The quantitative chemical composition analyzes of the phases were carried out by using energy dispersive spectroscopy (EDS), x-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) images and according to the EDX and XRD results and SEM images, Mg2Si, Al-3 Ni, Si and Al-9(Ni,Fe)Mg3Si5 phases were identified with in Al matrix phase. The lamellar spacing (lambda) for Mg2Si, Al3Ni, Si, and Al-9(Ni,Fe)Mg3Si5 phases were measured from transverse sections of the samples. The dependencies of lamellar spacing (lambda), microhardness and tensile-strength on growth rates were obtained as: lambda(Al3Ni) = 20.41 V-046, lambda(Mg2Si )= 24.54 V-0.52, lambda(si) = 31.62 V-0.51, lambda(Alg()(Ni,Fe)Mg3Si6) = 22.38 V-0.47, HV = 100.5 (V)(0.07), HV = 90.39 + 90.76(V)(0.25), sigma = 44.66 (V)(0.24), sigma = 2.62 + 245.73 V-0.25 respectively for the Al-Si-Mg-Ni eutectic alloy.