AZ31 magnesium alloy plates, which set up a Local Tensile Strain cracking tester, were welded using AC pulsed TIG welding machine. Effect of pulse frequency on crack sensitivity of welded AZ31 magnesium alloy was investigated. The longitudinal cracks appeared on center of the bead, which became clear, the solidification crack after observation of fractured surface using SEM. Regardless of the welding conditions, appearances of the solidification crack have a tendency to depend on the pulse frequency, and it is recognized that the solidification crack sensitivity decreases with the frequency of 30 Hz. The lengths of solidification cracks have a tendency to depend on the grain size on the fusion zone. This phenomenon is possibly explained by the fact that cracks did not easily propagated on the fusion zone because the applied stress is dispersed in fine grain. The solidification cracks of TIG welded AZ31 magnesium alloy were occurred by restraint stress due to the deformation during welding process and could not recognized the influence of the segregation of compounds on the fusion zone.
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