Heat Treatment of Cast and Cold Rolled Al–Yb and Al–Mn–Yb–Zr Alloys

Veronika Kodetová,Lucia Bajtošová,Vladimír Mára,Sebastien Zikmund,Michal Leibner,Martin Vlach,Hana Kudrnová,Miroslav Cieslar,Jaroslav Málek

doi:10.3390/ma14237122

Veronika Kodetová, Lucia Bajtošová + Show 7 more

Open Access

https://doi.org/10.3390/ma14237122

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Abstract

The microstructure, electrical properties and microhardness of as-cast and cold rolled AlYb and AlMnYbZr alloys were investigated. The addition of Mn, Yb and Zr has a positive influence on grain size. A deformed structure of the grains with no changes of their size was observed after cold rolling. The Al3Yb particles coherent with the matrix were observed in the AlYb alloys. The size of the particles was about 20 nm in the initial state; after isochronal treatment up to 540 °C the particles coarsen, and their number density was lower. The deformation has a massive effect on the microhardness behavior until treatment at 390 °C, after which the difference in microhardness changes between as-cast and cold rolled alloys disappeared. Relative resistivity changes show a large decrease in the temperature interval of 330–540 °C which is probably caused by a combination of recovery of dislocations and precipitation of the Al3(Yb,Zr) particles. Precipitation hardening was observed between 100 and 450 °C in the AlYb alloy after ageing at 625 °C/24 h and between 330 and 570 °C in the AlMnYbZr alloy after ageing at 625 °C/24 h.

Highlights

Four of the heaviest rare earth elements (RE = Er, Lu, Tm and Yb) can, to Sc, exhibit an Al3RE phase with a stable L12 structure [1,2,3,4]
Two as-cast alloys (AC) with a chemical composition Al–0.6Yb in wt.% (AlYb) and Al–0.11Mn–0.92Yb–0.12Zr in wt.% (AlMnYbZr) were cold rolled with a reduction thickness of 40% (CR40) and 70% (CR70)
The electron back-scattered diffraction (EBSD) observation in different locations across the sample shows that the addition of manganese (Mn) and zirconium (Zr) to the AlYb alloy together with higher addition of Yb causes a grain refinement

Summary

Introduction

RE elements are attractive additions to Al-based alloys for many reasons: (a) RE form Al3(Sc1−xREx) precipitates with the L12 structure, thereby replacing the expensive Sc; (b) diffusivity of RE in Al, which is bigger than of Zr or Ti [1,5]; (c) RE increase the lattice parameter mismatch between α-Al and Al3(Sc1−xREx) precipitates [6,7]. Despite several studies on cast Al–Yb(–Zr) alloys (e.g., [1,2,3,4,11,21,22]) there is a lack of a complex characterization of the Al–Yb(–Zr) system, a lack of knowledge on the influence of high temperature treatment and especially of the influence of deformation on precipitation behavior of Al-based alloys with Yb and Zr addition. The influence of isothermal ageing at 625 ◦C for 24 h on the microhardness and microstructure of the alloys was discussed

Materials and Methods

Initial State of the As-Cast and Cold Rolled Alloys

Isochronal TreatmAlelnotyof the Alloys

Isochronal Treatment of the Alloys