Effect of multi-directional hot forging process on the microstructure and mechanical properties of Al–Si based alloy containing high amount of Zn and Cu

In this study, the hypoeutectic Al–7Si based alloy containing Zn and Cu was severely deformed with multi-directional forging (MDF) process at 200 °C. The samples were placed into an open die allowing the free deformation in only one direction and forged with hydraulic press at cumulative strains of 2.07, 4.14 and 6.21. The microstructural examinations were performed with X-ray diffractometer, optical, scanning and transmission electron microscopies while their strength properties were determined by tensile and hardness tests. MDF led to a refinement in α-Al grains, hard Si, Al7Cu2Fe and Al2Cu particles of crystallization origin. This process also provided a method for formation of secondary precipitates within the alloy's microstructure. It was determined that MDF increased the tensile properties of the alloy but decreased its hardness. On the other hand, this process converted brittle type fracture of homogenized alloy to ductile type. These results were explained in terms of grain boundary strengthening, precipitation hardening, refining of hard particles, and softening in matrix due to dynamic recovery and recrystallization mechanisms. © 2020 Elsevier B.V.