Effecf of Ultra Sonic Vibration and Electromagnetic Stirring on the Properties of Ti and Ti Alloy Welds

Abstract

Pure Ti and Ti alloy are generally welded by TIG or MIG welding method. Sometimes fine porosities are detected in these welds by a X-ray examination. It seems that these porosities decrease the fatigue strength in some case. So it is important to protect the pure Ti and Ti alloy welds from these porosities. A study was carried out to make clear the effect of the ultrasonic vibration and the electromagnetic stirring on the porosities. At the same time, the effect of these two methods on the grain refinement, the bead shape, the penetration and the spatter were investigated. It was concluded that :
(1) the ultrasonic vibration
(i) The porosities of the TIG Welds were reduced by the ultrasonic vibration (9KC, 0.5-2 KW out put)
(ii) The grains of the MIG Welds were made finer by the ultrasonic vibration (9KC, 0.5-2 KW out put)
(2) the electromagnetic stirring
(i) The porosities of the TIG Welds were reduced by the electromagnetic stirring. (DC or 60c/s AC and 2000 AT.)
(ii) When using the coarse surface welding wire or with the machine oil on the groove surface, the porosities increase. But even in these cases by the electromagnetic stirring the porosities were considerably reduced.
(iii) The grain of the TIG or MIG welds made finer by the electromagnetic stirring, especially in the Ti alloy MIG Welds.
(iv) The frequency of the coil current was changed between DC and 60c/s AC The most effective frequency was around 8c/s.
(v) In case of MIG Welding, the spatter increased with the intensity of the magnetic field.
(vi) The bead shape was changed according to the frequency of the electromagnetic stirring. The bead was the concave type around 30 c/s, but tended to chahge into the convex type gradually with a decrease of the frequency.
(vii) The penetration decreased with the intensity of the magnetic field, especially in case of MIG Welding.