STRUCTURAL DEVELOPMENT DURING THE EXTRUSION OF RAPIDLY SOLIDIFIED AL-20SI-5FE-3CU-1MG ALLOY

An investigation concerning the changes of powder structure and microstructure during the extrusion of an important Al-Si-Fe-Cu-Mg alloy prepared from rapidly solidified powder has been carried out. The fragmentation of needle-shaped intermetallics in the alloy has been regarded as one of the main features of the process, which happens concurrently with the interparticle bonding and the shaping of the porous billets. The as-extruded microstructure is found to be mainly composed of the dynamically recovered alpha-Al matrix with numerous microcells, which are retained because of the inhibiting effect exerted by massive, fine second-phase particles on cell wall motion. Some recrystallized grains are also observed but their growth is effectively prevented. The refined intermetallics together with massive silicon particles and precipitates dispersed in the matrix can be expected to improve the thermal stability and high-temperature strength of the alloy to a great extent.