Journal Published Online: 08 November 2019
Volume 9, Issue 2

Effect of Multidirectional Forging with Decreasing Temperature on the Microstructure and Microhardness of the Aluminum-Magnesium-Scandium-Zirconium Alloy

CODEN: MPCACD

Abstract

Evolution of the microstructure and microhardness of the cast and homogenized aluminum alloy 1570C (aluminum [Al]-5 magnesium [Mg]-0.18 manganese [Mn]-0.2 scandium [Sc]-0.08 zirconium [Zr], wt. %) were studied under multidirectional forging (MDF) with decreasing the temperature. Sequential compression passes were performed at a strain rate of 10−2 s−1 with 90° changing of the loading axes from pass to pass; with the strain per pass of Δe = 0.7 and the 25°C decrease of temperature in each pass, starting from 450°C (T = 0.8 Tm). It has been shown that the alloy ductility was sufficient for straining the samples without cracking up to the total strain of Σe = 10.5 at 100°C (about 0.4 Tm). In the initial state, the alloy possessed a coarse-grained structure with a grain size of about 25 μm and a uniform distribution of the Al3(Sc,Zr) nanoscale aluminides. MDF led to a continuous grain refinement. At relatively low strains, Σe ≤ 4.2 (and high temperatures, T ≥ 325°C), new grains were evolved mainly in the mantle areas of initial grains, resulting in the formation of a bimodal (sub)grain structure, which persisted up to Σe = 8.4 (T = 175°C). During further MDF, the alloy structure became more homogeneous and fine-grained, and at Σe = 10.5 (T = 100°C), it almost completely transformed into a nanocrystalline grain structure with a crystallite size of 100–150 nm, stabilized by nanodispersed Al3(Sc,Zr) precipitates. The average size of the deformation-induced (sub)grains in the whole range of strains (temperatures) studied obeyed a power-law function of the flow stresses with the exponent close to −0.75. The microhardness testing showed that MDF did not lead to the notable alloy hardening in the samples deformed at relatively high temperatures (T > 325°C) and low strains (Σe < 4.2). With further processing, in contrast, a significant (about 1.5 times) hardness increase took place in accordance with the Hall-Petch relationship.

Author Information

Sitdikov, O. S.
Department of Light Alloys, Institute for Metals Superplasticity Problems of Russian Academy of Science, Ufa, Russia
Avtokratova, E. V.
Department of Light Alloys, Institute for Metals Superplasticity Problems of Russian Academy of Science, Ufa, Russia
Murzinova, M. A.
Department of Light Alloys, Institute for Metals Superplasticity Problems of Russian Academy of Science, Ufa, Russia
Markushev, M. V.
Department of Light Alloys, Institute for Metals Superplasticity Problems of Russian Academy of Science, Ufa, Russia
Pages: 16
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Stock #: MPC20190006
ISSN: 2379-1365
DOI: 10.1520/MPC20190006