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Microstructural evolution of an A356 aluminum alloy processed by
accumulative back extrusion
N. Haghdadi1,2, A. Zarei-Hanzaki2, P.D. Hodgson1
for Frontier Materials, Deakin University, Waurn Ponds, VIC 3216, Australia
2School of Metallurgy and Materials Engineering, College of Engineering, University of
Tehran, 11365-4563 Tehran, Iran
1Institute
Abstract
A356 aluminum alloy is one of the most common cast aluminum alloys, the
microstructure of which consists of an aluminum matrix and eutectic silicon particles.
Coarse and long Si particles are the main reason for the limited mechanical properties
of this alloy. In order to spheroidize and refine the silicon particles, accumulative back
extrusion (ABE) process was applied on a thixocast A356 aluminum alloy in the current
study. The results indicate that the eutectic Si platelets are fragmented and
spheroidized as a result of applying severe deformation at high temperatures.
Mechanical fragmentation and thermal disintegration play a prominent role in Si particle
break up. The average particle size decreased with decreasing temperature while
spheroidization was enhanced with increasing ABE temperature. The current work also
made use of finite element analysis (FEA) to study the evolution of the equivalent strain
distribution across the severely deformed specimens during ABE processing. The FEA
results show that the strain distribution in the cross-section after step one (i.e., back
extrusion) is inhomogeneous, while it tends to be reasonably homogenous after
applying the second step (i.e., constrained back compression).
Keywords: A356 Aluminum alloy; ABE; Spheroidization; Finite element analysis
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