Effects of CaF₂ Coating on the Microstructures and Mechanical Properties of Tungsten Inert Gas Welded AZ31 Magnesium Alloy Joints

The effects of CaF₂ coating on the macromorphologies of the welded seams were studied by morphological analysis. Microstructures and mechanical properties of butt joints welded with different amounts of CaF₂ coatings were investigated using optical microscopy and tensile tests. The welding defects formed in the welded seams and the fracture surfaces were analyzed by scanning electron microscopy. An increase in the amount of CaF₂ coating deteriorated the appearances of the welded seams but it improved the weld penetration depth and the depth/width (D/W) ratio of the tungsten inert gas (TIG) welded joints. The α-Mg grains and Mg₁₇(Al,Zn)₁₂ intermetallic compound (IMC) were coarser in the case of a higher amount of CaF₂ coating. The increase in the amount of CaF₂ coating reduced the porosities and total length of solidification cracks in the fusion zone (FZ). The ultimate tensile strength (UTS) value and elongation increased at first and then decreased sharply.