The material used in the study was an as cast AZ91D
magnesium ingot, whose chemical composition is shown
in Table 1. The ingot was sliced into plates of about 3–
5 mm in thickness and ,100650 mm in size using a
band saw. A Miller Shopmaster TIG welding machine
was used to weld the magnesium plates in the form of
butt joints. In some cases, welding beads were deposited
on the plates for metallurgical study. Before welding,
sand paper was used to remove the oil and dirt on the
surface of the plates. This was found to help to prevent
the formation of porosity in the welds.
The welding was conducted using alternating current
at a voltage of 20–22 V and current in a range from 60
to 120 A. The welding torch was attached onto an
autorunning machine in order to make it travel at a
constant speed of ,5 mm s21
. The welding was autogenous and no filler rod was ever used.
Metallographic samples were extracted from the base
plate and welded joints, etched in ethylene glycol
solution (20 mL acetic acid, 60 mL ethylene glycol,
1 mL HNO3
and 20 mL water) for 30–50 s, and
observed using the scanning electron microscopes
(SEM). The distributions of alloy elements in all samples