The influence of equal channel angular pressing angles on the microstructure and properties of Al-Si-Mg alloy
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Date
2006
Authors
Al-Jubouri, Ali Abadi Altayef
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Abstract
The aim of this research is to improve the physical and mechanical
properties of Al-Si-Mg alloy by grain structure refinement produced by severe
plastic deformation through equal channel angular pressing (ECAP). This alloy
has a composition (in wt. %) of 1.3 Si, 0.3 Mg, 0.18 Fe, 0.023 Cu, 0.019 Mn,
0.017 Zn, and 0.014 Ga, 0.011 Ti 1.3 Si, 0.3 Mg, 0.18 Fe, 0.023 Cu, 0.019 Mn,
0.017 Zn, 0.014 Ga, 0.011 Ti balance Al. In ECAP process, the workpieces are
pressed through a 1200 and 900 dies using route BC. Through this route the
sample is rotated by 900 in the same direction between each consecutive
pressing through the ECAP dies. Workpieces undergo plastic deformation by
pure shear through the intersecting corner. Microstructure evaluation, physical
and mechanical properties of the extruded Al-Si-Mg workpieces by equal
channel angular pressing were conducted using scanning electron microscopy
(SEM), micro-Vickers hardness tester, tensile test machine, heat conduction
apparatus and auto lab corrosion test system. The effect of die angles on the
microstructural refinement and mechanical properties at annealing temperature
(230 0C and 500 0C) and deformation temperature (600 0C) were investigated.
From the microstructure evolution, ECAPed resulted in reduction of grain size
from 70-100 m to about 200nm. The ECAPed workpieces that underwent
annealing at 500 0C for 24h before ECAP also displayed grains with similar
sizes. However, annealing process at 230 0C for 20-30min after ECAP leads to
an increase of grain size to around 300 to 600nm. Microhardness was
improved by 250-300% and there was slight reduction in its value obtained with
the increase in annealing time of ECAPed workpieces. The enhancement of
thermal conductivity is by 19-30%, depending on channel angle and annealing
conditions. It showed higher value for sharper channel angle (900), and higher
annealing temperature. From the tensile tests, the maximum load, maximum
stress and elongation to failure increases with the number of passes through
the ECAP die. Results from the corrosion experiments of deformed Al-Si-Mg
alloy in 3.5% NaCl solution showed better corrosion resistance compared to ascast
Al-Si-Mg alloy. The corrosion rate was reduced with the number of passes
through the ECAP dies but its value increases with increasing annealing
temperature. In general, a drastic change in all investigated mechanical and
physical properties occurred after the first pass through the ECAP dies. It is well
known that the ECAP provides a simple, cheap and effective processing
technique for producing nanostructured Al-Si-Mg alloy. Consequently the
improvement in the mechanical and physical properties offers great potential to
be used in various industrial applications.
Description
PhD
Keywords
Materials and Mineral Resources Engineering , Channel angular , Al-Si-Mg alloy