Influence of the dendritic microstructure and β-Al5FeSi phase on the wear characteristics in a horizontally solidified Al-7Si-0.4Mg-1.2Fe alloy

Abstract

In this work an Al-7Si-0.4Mg-1.2Fe alloy (wt.%) was subjected to a horizontal solidification experiment using a water-cooled solidification device equipped with thermocouples to obtain temperature vs. time data which in turn allowed solidification thermal parameters, such as growth and cooling rates (VL and TR, respectively), to be determined. In turn, tribological behavior of samples with different secondary dendritic spacing (λ2) and β-Al5FeSi platelets length (βFe) were assessed by means of dry sliding wear testing performed in a rotating fixed ball machine, with wear volume and rate (WV and WR, respectively) being the two main investigated wear parameters. Quantitative metallography by optical and scanning electron microscopy along with energy dispersive X-ray spectroscopy enabled both as-cast microstructures and worn craters to be characterized. More significant variations in wear resistance of the investigated alloy were found for ranges of λ2 and βFe that lie within 12−20 μm and 14–36 μm, respectively, with the coarsening of the microstructure constituted by Al-rich primary phase dendrites surrounded by α-Al + Si + θ-Mg2Si + β-Al5FeSi eutectic structures favoring reduced WV and WR values. For λ2 and βFe values higher than 24 and 48 μm, respectively, both WV and WR stabilize assuming constant values that depend on the sliding distance. In addition to power type equations relating λ2 and βFe to VL and TR, mathematical expressions for variations of WV and WR with λ2 and βFe are also proposed. Finally, a comparative analysis with the literature is presented.