Ultrafine-Grained Plates of Al-Mg-Si Alloy Obtained by Incremental Equal Channel Angular Pressing: Microstructure and Mechanical Properties

Abstract

In this study, an Al-Mg-Si alloy was processed using via incremental equal channel angular pressing (I-ECAP) in order to obtain homogenous, ultrafine-grained plates with low anisotropy of the mechanical properties. This was the first attempt to process an Al-Mg-Si alloy using this technique. Samples in the form of 3 mm-thick square plates were subjected to I-ECAP with the 90 deg rotation around the axis normal to the surface of the plate between passes. Samples were investigated first in their initial state, then after a single pass of I-ECAP, and finally after four such passes. Analyses of the microstructure and mechanical properties demonstrated that the I-ECAP method can be successfully applied in Al-Mg-Si alloys. The average grain size decreased from 15 to 19 lm in the initial state to below 1 lm after four I-ECAP passes. The fraction of high-angle grain boundaries in the sample subjected to four I-ECAP passes lay within 53 to 57 pct depending on the examined plane. The mechanism of grain refinement in Al-Mg-Si alloy was found to be distinctly different from that in pure aluminum with the grain rotation being more prominent than the grain subdivision, which was attributed to lower stacking fault energy and the reduced mobility of dislocations in the alloy. The ultimate tensile strength increased more than twice, whereas the yield strength was more than threefold. Additionally, the plates processed by I-ECAP exhibited low anisotropy of mechanical properties (in plane and across the thickness) in comparison to other SPD processing methods, which makes them attractive for further processing and applications.

Effect of microstructural features on the corrosion behavior of severely deformed Al–Mg–Si alloy

“…[ 23 ] A detailed analysis of the microstructure evolution of the material during the processing was presented in our previous work. [ 24 ]…”

Generalized Stacking Fault Energies of Aluminum Alloys–Density Functional Theory Calculations

“…Mg-0.43%wt. Si alloy is distinctly different from that in pure aluminum, with the grain rotation being more prominent than the grain subdivision due to lower stacking fault energy and the reduced mobility of full dislocations in the alloy [29,31]. Other experimental work has found that Mg and Si concentration in Al impact on the deformation mechanism and grain size in aluminum alloys [15,17,30,32].…”

Ultrafine‐Grained Plates and Sheets: Processing, Anisotropy and Formability

“…It should be noted that such a high HAGB value is difficult to achieve by means of individual process. For instance, a single processing using mtECAP (four passes) resulted in a fraction of HAGBs of ≈40–60%, which is typical for ECAP‐based processes …”

“…Commercially, pure aluminum after eight I‐ECAP passes exhibits a homogeneous, fully equiaxial (in 3D) microstructure with an average grain size of below 1 μm and a high content of HAGBs (≈80%) . Processing the Al–Mg–Si alloy up to four passes already resulted in a grain size decrease to below 1 μm and a fraction of HAGBs of above 50% …”