Effect of existing form of alloying elements on the microhardness of Al–Si–Cu–Ni–Mg piston alloy

Effect of alloying elements including Si, Cu, Ni and Mg with different existing forms on the microhardness of Al–12Si–4Cu–2Ni–2.6Mg (in wt.%) piston alloy was investigated. It is found that microhardness of the alloy reaches to 1.88 GPa when all the Cu, Ni, Mg and 3.63 wt.% Si dissolved in the α-Al matrix, and increases to 2.02 GPa while only the solid-solved Si precipitates to form nanoparticles. The precipitated Si has greater contribution to the alloy's microhardness than the solid-solved Si in the same level. Furthermore, the precipitation of intermetallics containing Cu, Ni and Mg that disperses in the Al-matrix can further improve the microhardness to 2.09 GPa. The hardening efficiency of the intermetallics precipitation of Cu, Mg and Ni on microhardness is less than that of the nanoscale Si precipitates under the same mass fraction. For Cu, Mg and Ni alloying elements, whether dissolving in α-Al matrix or precipitating as nanoparticles, there is no evident difference on improving microhardness of the tested alloy.

From the upper graph, it is found that microhardness of the alloy reaches to 1.88 GPa when all the Cu, Ni, Mg and 3.63 wt.% Si dissolved in the α-Al matrix, and increases to 2.02 GPa while only the solid dissolved Si element precipitates to form nanoparticles. Furthermore, the precipitation of intermetallics containing Cu, Ni and Mg that disperses in the Al-matrix can further improve the microhardness to 2.09 GPa. So the precipitated Si has greater contribution to the alloy's microhardness than solid-solved Si in the same level. The hardening effect of the precipitation of Cu, Mg and Ni on microhardness is less than that of the nanoscale Si precipitates. For Cu, Mg and Ni alloying elements, whether dissolved in α-Al matrix or precipitated as nanoparticles, they have similar effect on improving microhardness of the tested alloy.Figure optionsDownload as PowerPoint slideHighlights
► The effect of alloying element's existing form on microhardness is investigated.
► The precipitated Si has greater contribution than that of solid-solved Si.
► Whether dissolving or precipitating, Cu, Mg and Ni have the similar impact.
► But the effect of precipitated Cu, Mg and Ni is less than that of Si precipitates.