Structure of the aluminum alloy 1570C subjected to multidirectional forging with decreasing temperature

O.S. Sitdikov, R.N. Garipova, E.V. Avtokratova, O.E. Mukhametdinova, M.A. Murzinova, M.V. Markushev

Abstract

The structure of cast and homogenized aluminum alloy 1570C (Al5Mg0.18Mn0.2Sc0.08Zr, wt. %) was studied after multidirectional isothermal forging (MIF). Repetitive upsetting was carried out with changing the loading axis, a 25°C decrease of temperature at each pass starting from 450°C, a pass strain of 0.7 and strain rate of about 10–2 s–1. The alloy ductility was sufficient for a successful (without cracking) straining of the sample up to е ~ 10.5 at 100°C. In the initial state, the alloy possessed a coarse-grained structure with a grain size of about 25 μm and uniform distribution of the nanoscale aluminides Al3(Sc,Zr). MIF resulted in continuously refined (sub)grains and remarkable material hardening. At low strains (е ≤ 4.2) and high temperatures (Т > 325°С), new grains were developed mainly in the mantle regions of the initial grains. As a result, a bimodal structure was formed, which persisted up to strains about 6.3 (250°C). With further MIF, the newly evolved grain structure became more homogeneous and occupied practically the whole material volume. Electron microscopy showed that a nanocrystalline structure with a crystallite size of 100 – 170 nm and a uniform distribution of dispersoids was developed. The deformation structure was characterized by a high dislocation density that is attributed to a decelerating rate of dynamic recovery under decreasing temperature. It is worthy of note that the structure developed in the alloy was close in its characteristics to that observed in some fcc or hcp alloys after high pressure torsion at room temperature. However, in the last case, the sample volume and dimensions were significantly smaller than those after MIF.

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