Influence of plasma arc welding heat treatment on microstructure and magnetic properties of 1J85 permalloy welded joints

This study addresses the issue of magnetic property degradation during the welding of 1J85 permalloy. Comparative experiments are conducted on 1.5 mm thick annular 1J85 permalloy using two processes： plasma arc welding （PAW） and plasma arc heat treatment welding （PAHTW）， to systematically investigate the effects of these processes on the microstructure and magnetic properties of welded joints. The microstructure， elemental distribution， magnetic permeability and coercivity of the joints are analyzed using optical microscopy， scanning electron microscopy， energy-dispersive spectroscopy， and soft magnetic property testing. The results show that under the PAW process， the morphology of the weld joint exhibits a funnel-shaped structure with a wider top and narrower bottom； under the PAHTW process， multi-layered regional boundaries are formed in the weld zone， with significant grain growth， reduced number of cellular subcrystals， and decreased grain boundary density. Energy-dispersive spectroscopy analysis indicates that the content of the non-magnetic element Si in the weld zone relatively reduces by approximately 50% compared with that in the PAW process. Compared with the PAW process， after PAHTW treatment， the initial magnetic permeability of the joint increases from 40.12 mH/m to 78.81 mH/m， the maximum magnetic permeability increases from 72.63 mH/m to 113.41 mH/m， and the coercivity decreases from 1.70 A/m to 1.24 A/m.