The influence by hydrostatic extrusion on the microstructure and extrudability of the IM processed hypereutectic Al–Si–X alloys

Hypereutectic Al–Si alloys containing various Si contents of 12–20 wt.% and an Al–18 wt.%Si–5 wt.%Fe–0.2 wt.%Ti–0.2 wt.%B–0.02 wt.%Sr alloy were fabricated via ingot metallurgy (IM) process prior to hydrostatic extrusion with various extrusion ratios. As increasing the Si content in the hypereutectic Al–Si alloys, the extrusion pressure load increases, linearly. Furthermore, for the same level of extrusion ratio the extrusion pressure obtainable is seen to dramatically increase as the Si content, in the present alloy system, increases. In the present hydrostatic extruded materials, it is clearly conformed that eutectic Si and primary Si particles are refined during extrusion process, and the extent of refining microstructures increases as increasing extrusion ratio. The average particle sizes of primary Si of the as-extruded materials were 30 μm, for the Al–18Si, and 10 μm for the Al–18Si–5Fe–0.2Ti–0.2B–0.2Sr alloy. This indicates that the average grain sizes of Si particles in Al–Si alloys were bigger than those of the ingot material treated with refining elements. From the above results, it is suggested that the hydrostatic extrusion processing can lead to development of hypereutectic Al–Si–X system alloys as new functional aluminum alloys with hard and fine dispersoids.