Effect of Friction Stir Processing on the Microstructure and Mechanical Properties of Iron-Bearing A356 Cast Aluminum Alloy

In the recycled aluminum alloys, iron is the most common impurity, usually deleterious to their mechanical properties, especially the ductility of the alloys. In this study, effect of friction stir processing (FSP) was studied on the microstructure and mechanical properties of standard and Fe-bearing A356 cast Al alloys. For this purpose, A356 and A356-1.2 wt.% Fe base metals were prepared in the form of plates by gravity casting in a steel mold and FSPed with parameters 1000 rpm rotational speed, 50 mm/s traverse speed, 2 degrees tool tilting angle, and 0.2 mm plunging depth. The microstructure and mechanical properties of FSPed samples were studied and compared to those of the as-cast base metals. The results revealed that addition of Fe to A356 refined microstructure and increased fraction of acicular beta-AlFeSi intermetallic compounds (Fe-IMCs) which in turn increased strength (6%) but reduced ductility (15%) of A356-Fe base metal compared to the standard A356. FSP fragmented both acicular Si and Fe-IMCs and redistributed them uniformly in the structure. The FSPed sample containing 1.2 wt.% Fe shows tensile strength as high as 211 MPa and at the same time elongation of 25% which are 23% and 147% higher than those of the cast base metal. The present results prove the beneficial effects of FSP on the problems associated with Fe residue in the recycled Al alloys.