Mechanical properties of TIG welded joints on heavy AZ31 magnesium alloy plates

摘要

The mechanical characteristics of TIG butt welded joints on 20mm thick AZ31B-O magnesium alloy plates with a plate thickness of 20 mm were evaluated, and as a result of comparisons with the base material, the following knowledge was obtained. In tensile tests at normal temperatures and high temperatures and in impact tests at normal temperatures, there was no large difference found between the base material and the welded joints; on the other hand, in high temperature creep tests and normal temperature fatigue tests, the welded joints were clearly inferior to the base material. The tensile strength of the base material and the welded joints in the tensile tests was substantially the same and the welding efficiency was close to 100percent, but the tensile strength of the welded joints did not exceed that of the base material at any test temperature. The elongation is substantially the same for the two up to 473 K, and the elongation of the base material increases at 523 K or greater, but the value is substantially fixed for the welded joint at 473 K and above. In high temperature creep tests, along with the transition from steady creep to accelerated creep in the welded joint being early, fracture occurs without a large amount of necking, so the creep fracture time and creep fracture elongation are smaller than those for the base material. 0However, the difference in the steady creep speed for the welded joint and the base material is small. In high temperature creep deformation, cavities form on the crystal grain boundaries in the welded metal parts, combine with each other and progress to fracture, so the progression to fracture comes without a large amount of necking. On the other hand, with the base material, cavities that were elongated in the direction of the load were observed, and since the form was such that it was difficult for them to connect with each other and cause fracture, fracture occurred with a large amount of necking. In impact tests, the impact value was a little larger in the LB direction for the base material than for the LH direction. For the welded joints, there was no difference due to the direction, and the value was substantially the same as that for the LH direction for the base material. In the fatigue tests, the welded joints had a lower number of cycles than the base material, or fracture occurred at a lower repeated stress. With a fatigue limit of 10~7 cycles, the base material was estimated at approximately 50 MPa and the joint at approximately 45 MPa.