The Evolution of Homogeneity in a Transverse Cross Section of Aluminum Alloy Proﬁle Deformed by Twist Extrusion SHAHAB RANJBAR BAHADORI 1 and SEYED ALI ASGHAR AKBARI MOUSAVI 1,2 1.—School of Metallurgy and Materials Engineering, University College of Engineering, Univer- sity of Tehran, P.O. Box 11155-4563, Tehran, Iran. 2.—e-mail: akbarimusavi@ut.ac.ir Twist extrusion (TE) has been proposed as a way to produce homogeneous ultraﬁne-grained microstructure in aluminum alloys, with consequent improvement in properties. Performing different thermomechanical processes, including natural and artiﬁcial aging and sequential passes of TE, produced noticeably homogeneous proﬁles. As a consequence of the strain distribution pattern from TE (which was heterogeneous throughout the transverse section) and the existence of precipitates of different sizes across the section, a homogenous grain distribution resulted. It was shown that the balance of two different strengthening mechanisms of grain size and second-phase particles, at the center and corner, caused a mechanically homogenous section. INTRODUCTION Recently, the processing of polycrystalline mate- rials through severe plastic deformation (SPD) methods has been the focus of metal forming research to produce ultraﬁne-grained and nano- grained microstructures. 1–3 SPD includes several different techniques such as equal-channel angular pressing, 4 high-pressure torsion, 5 accumulative roll bonding, 6 multidirectional forging, 7 repetitive cor- rugation and strengthening, 8 and a more recently developed method called twist extrusion (TE). 9–11 TE was introduced by Beygelzimer et al. 12 In this process, a workpiece is extruded by hydrostatic pressure through a twisted channel with a rotation angle (a) and a slope angle (b) (Fig. 1). Because the billet’s original geometry is returned at the end of the process, it is possible to deform it repeatedly in order to accumulate strain. 13,14 Previous studies simulated the strain difference across the transverse cross section of a Ti-6Al-4V billet. 15 Moreover, Beygelzimer et al. 16 modeled the strain distribution and the velocity ﬁeld on the transverse cross section of the billet. These theo- retical and experimental studies showed that the strain dispersion was not homogeneous throughout the transverse cross section of the processed work piece as the peripheral regions experience more strain than the center. The maximum and minimum strains after one pass of TE can be calculated by the following equations 17,18 : e min  0:4 þ 0:1 tan b (1) e max  2 ﬃﬃﬃ 3 p tan b (2) As a result of the strain heterogeneity, the distri- bution of grain size and mechanical properties is not constant across the transverse section, and conse- quently, the processed specimens did not have acceptable quality. 17,18 The next experiments aimed at solving this problem. Orlov et al. 19 analyzed the microstructure evolutions of Al 1100 alloy during repeated passes of TE and also examined the macro- ﬂow patterns and mechanical properties. 20 They found that performing repeated passes of TE decreased the microstructure and mechanical het- erogeneity of the transverse section signiﬁcantly. Later, more experiments were conducted by using conventional forming techniques, such as rolling and direct extrusion, after TE to create homoge- nized product. 21,22 However, none of these methods resulted in a reasonably homogenous product. This work presents thermomechanical processing, including natural and artiﬁcial aging heat treat- ments and sequential TE passes, as a new way to JOM, Vol. 64, No. 5, 2012 DOI: 10.1007/s11837-012-0305-5 Ó 2012 TMS (Published online April 20, 2012) 593