Abstract:

The six-axis robot was employed to weld AZ31 magnesium alloy plates. The automatic arc welding parameters of the AZ31 magnesium alloy plates were investigated in detail. After welding, microstructure, precipitates, and tensile properties of AZ31 joint were studied by using the optical microscope, scanning electron microscopy, X-ray diffraction and universal testing machine. A sound joint was obtained under the welding parameters: welding current 160 A, welding speed 0.45 m/min, wire speed 0.6 m/min, distance between tungsten and plate (first half 0.5 mm, later half 2.0 mm), front face shielding gas 16 L/min, and back face shielding gas 21 L/min. The microstructure of AZ31 auto-welded joints consisted of base metal (BM), heat affected zone (HAZ), and fusion zone (FZ). A large amount of the hard β-Mg17Al12 phases were formed in FZ and HAZ. The ultimate tensile strength of the AZ31 joint was up to 80.02% of the BM. The fracture surface of the tensile specimen exhibited obvious ductilebrittle mixed facture, which were characterized by some dimples and cleavage surfaces.

Key words: AZ31 magnesium alloy, mechanical properties, microstructure, automatic arc welding, β-Mg17Al12