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

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 (V-L and T-R, respectively), to be determined. In turn, tribological behavior of samples with different secondary dendritic spacing (lambda(2)) and beta-Al5FeSi platelets length (beta(Fe)) were assessed by means of dry sliding wear testing performed in a rotating fixed ball machine, with wear volume and rate (W-V and W-R, 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 lambda(2) and beta(Fe) that lie within 12-20 mu m and 14-36 mu m, respectively, with the coarsening of the microstructure constituted by Al-rich primary phase dendrites surrounded by alpha-Al + Si +theta-Mg2Si + beta-Al5FeSi eutectic structures favoring reduced WV and WR values. For lambda(2) and beta(Fe) values higher than 24 and 48 mu m, respectively, both W-V and W-R stabilize assuming constant values that depend on the sliding distance. In addition to power type equations relating lambda(2) and beta(Fe) to V-L and T-R, mathematical expressions for variations of W-V and W-R with lambda(2) and beta(Fe) are also proposed. Finally, a comparative analysis with the literature is presented.