Research On Arc Welding Resistant Ability Of AgMeO Contact Materials For Automobile Relays

Electrical contact is the key component of relays. Its performance affects the reliability of electrical power system greatly. With the implement of environment restriction from the European Union and the improving from 14V to 42V of the power supply in automobile, the requirement to the electrical contact materials for automobile relays will be more rigorous. Contact welding because of arc is the most serious failure phenomenon. Theoretic analyses for welding phenomena can give the guidance to the research and development of contact materials.The heat and flow process during contact welding by arc is investigated by numerical method, and correlative factors which can affect the welding resistant ability of the AgMeO contact material are discussed. The axial symmetry model of cylindrical contact under arc is set up. The temperature distribution, velocity distribution and content distribution are calculated by the Finite Volume Method.The results show that the weld molten pool is on the local area of the contact and its size is small. The gradient of temperature distribution is on the order of 107K/m, and the rate of temperature change is on the order of 107K/s. Changes the thermal conductivity,heat capacity,decomposition temperature or decomposition enthalpy of the MeO phases give little benefit to improve the welding resistant ability of the AgMeO contact material. The fluid flow in weld pool is mainly driven by surface tension. The effect of the flow driven by electromagnetic force and buoyancy force is weak. The negative value of surface tension temperature coefficient causes near surface fluid moving from the centre to the periphery, the shape of the pool become shallow and wide. The positive value of surface tension temperature coefficient for causing near surface fluid moving from the periphery to the centre results in a very deep pool. The content of the MeO on the surface of the contact increases because of the fluid flow. The bigger size of the MeO particle is, the more obvious the segregation is. The segregation of MeO on the contact surface increases the welding area and decreases the welding strength of the contact material.Adding some appropriate element in contact material may be an efficient means to improve the welding resistant ability. By the additive, the arc duration can be shorter and the arc can be more dispersed on the electrical contact. The additive which changes the surface tension temperature coefficient can make the weld pool shallow.An apparatus which simulates the contact action is designed to test the weld performance of the real electrical contact material. The movement of the contacts is controlled by electromagnet and springs. The contact force can be adjusted and the welding force can be measured. It is easy to assemble and disassemble the contacts.