Abstract

Industrial sectors with interest in welding magnetic materials include the aerospace, electrical and defence industries [1]. The effects of CO₂ laser welding and high temperatures (i.e. above the Curie temperature) on the magnetism of ferromagnetic materials were investigated. A 1.2 kW MFKP CO₂ laser was used to weld the magnetic material at a constant power of 1 kW in the CW mode, for different welding translation velocities. Figure 1 shows a schematic of the magnetic field measurement system. This consisted of two orthogonal translation tables and an RS miniature Hall effect Sensor (HES), attached to an outlying platform from the larger translation table. The x-y motion was controlled via a microprocessor so that the HES was translated over the entire surface of the welded magnets (2 Alcomax magnets: 8% Al, 11.5% Ni, 21% Co, 4% Cu, Fe). The signal from the HES was signal conditioned and fed into a data acquisition card located in the PC. The magnetic field strength over the laser weld and surface of the specimen was measured before welding, immediately after welding and 3 days after welding. Figure 2 shows the spatial differences in the magnetic properties of the sample immediately after welding and Figure 3 the corresponding data 3 days after welding. The magnetisation of the weld pool and HAZ was reduced immediately after welding; 3 days later, during which the samples were isolated, magnetism recovered over the specimen except in the weld zone where it had been damaged and stayed unrecovered. A high translation velocity maximised the remagnetisation process and reduced the demagnetised zone and HAZ.

© 1998 IEEE