alloys and the filler wire was AZ31 Mg alloy with the diameter of
1.6 mm. Table 1 shows the chemical compositions and mechanical
properties of base materials and filler wire. The thickness of the
AZ31 plate was 10 mm, while that of the AZ31B plate was 5 mm.
Before welding, they were milled to be 100 mm
×
100 mm and then
cleaned by acetone.
Fig. 1 shows the arrangement of heat sources, which has been
optimized in previous studies (Gao et al., 2009a,b). During welding,
a flat copper backing was used to force the formation of weld root.
The paraxial weld torch was 55◦ angle to the surface of workpiece by
using a He–Ar (3:2) mixed gas flux of 25 l/min. A coaxial gas nozzle
was employed to protect the focal mirror by using a pure argon
gas flux of 7.5 l/min. The distance between laser beam and wire tip
(DLA) was 3 mm, and the laser defocused distance was
−1 mm.
The study on the process characterization was carried out in
the configuration of bead-on-plate, while that on the joint characterization
was carried out in butt configuration. Table 2 shows the
welding parameter range used for process characterization. Table 3
shows the welding parameters selected for microstructure analysis
and tensile test. Table 4 shows the detailed arc parameters
corresponding to each current. Where P denotes the laser power,
I denotes the arc current, U denotes the arc voltage, v denotes the
welding speed, Q denotes the heat input, r denotes the wire feed
rate and f denotes pulse frequency of the arc. The heat ratio of arc
to laser was defined as HRAL and presented as follows: