Empirical models of mechanical behaviour of Al-Si-Mg cast alloys for high performance engine applications

Abstract

Substructure characteristics in hot worked Al
alloys are very important for modeling
mechanical properties during hot forming,
and also in the product. In contrast to simple
grain shape in etched-optical microscopy
(EOM), polarized optical microscopy (POM)
significantly confirmed subgrain presence in
better detail than x-ray diffraction (XRD).
Transmission electron microscopy (TEM)
revealed the dislocations forming subgrain
boundaries (SGB) and dispersed between
them; TEM in scanning mode (STEM) could
provide microtextures substantiating XRD.
Scanning electron microscopy with backscattered
image (SEM-EBSI) exhibited
substructures more accurately than POM but
much less detailed than TEM. Finally,
orientation-imaging microscopy (OIM)
provided microstructures as in SEM-EBSI and
also detailed misorientations; however,
omission of very-low angle SGB seen in TEM
gave rise to estimates of larger subgrain sizes
and misorientations. The field of view is very
limited in TEM, but fairly similar in POM,
SEM-EBSI and OIM although higher
magnifications are possible in the last two.
The various techniques are also affected
differently by substructure scale (temperature,
strain and rate) and composition that
also influence specimen preparation.
Examination by several techniques is best
assurance of correct interpretation of
microstructural characteristics.