Preparation And Basic Research On Ag-SnO₂ Electrical Contact Materials

This paper get the support of the project "Research of high-current relay materials",which is provided by department of defence(DOD), Yunnan province natural science foundation project " Computational material and application of computer simulation for materials ".This paper include processing of electrical contact materials Ag-SnO₂ and contrasting macrography performance and microscopic stucture. By using of metallurgical microscope,scanning-electron microscope(SEM) and energy spectrum analysis, we studied Ag-SnO₂ complex micromere,which formed by high-energy ball milling,and pyknosis, plastic working and deforming research, and the effect of partical size of SnO₂ on mechanical and electrical property of Ag-SnO₂ electrical contact materials.Follwing upward indicate that:(1) Ag-SnO₂ has higher hardness, high work-hardening, high resistance of deformation, but low elongation. Lower density and smaller grain size of SnO₂ result in higher strengthening effectiveness than other Ag-based metal oxides materials in same ratio by weigh.(2) High-energy ball milling will break and discrete SnO₂ particle in Ag-SnO₂ . In the first stage of ball milling, result is visible , dispersion is uniform and working property is increasing. Optimally technology of powder manufacturing is that: ratio of grinding media to material is 10:1; diameter of slide block is 25mm; time of ball-milling is 30min.(3) Macromechanics and electrical property of Ag-SnO₂ correlate with high-energy ball milling technology. With increasing time of ball milling ,particle of SnO₂ is tapered and strength and hardness increased ,but elongtiong decreased. When particle of SnO₂ less than 5μm, electrical property of contactor meet the requirement.(4) technology of Ag-SnO₂ powder pressing include that: organic lubricant, pressing force is 30MPa, dwell time is 5min; Optimally technology of Ag-SnO₂ sintering include that: heat treatment include two stages,in the first, temperature rise to 650℃quickly and keep for 30min; in the second stage, temperature also rise to 900℃quickly and keep for 5min. During sintering, Ag don't react with SnO₂ and the increasing of density and strength depend on bonding between Ag particles.(5) In the first stage of pyknosis of Ag-SnO₂ , agglomerated particle is broken, after that Ag particle remove and rearrange; In the medium stage , SnO₂ particle attach and welding-on Ag particle, Ag particle create plastic deformation and become polygon; In the last stage, when local pressure greater than receiving pressure of SnO₂ particle, it will create fracture and rearrange .(6) By researches on press rule of single constituent and multi-powders, verified by experimental findings and constitutive equation,the equation has been suggested as Each equation coefficient were calculated and verified, predictive accuracy is good.(7) The appropriate extruding processing parameters of the Ag-SnO₂ contact materials is that : the temperature is 800℃,the diameter is 8mm, the extrusion ratio is 100 and extruding times is 3.We can finish the hot -wire-drawing course which fromΦ8.0 toΦ1.5mm by the way of hot-die-wire-drawing, whose reduction in pass is 5%. We can make the cold-wire-drawing underΦ1.5mm,the reduction in pass also is 5%.(8)The deformation of the Ag-SnO₂ contact materials generate in the enrichment zone of Ag, but SnO₂ hasn't the phenomenon of being cut and deformed. It is only play the part in rejecting the modification and strengthening materials. These is 2 path to form the abruption crack of the Ag-SnO₂ contact materials. The one is generating flaw at the surface,expand from surface along the enrichment zone of Ag till it is broken, and the other is in the enrichment zone of SnO₂ ,where modification is diffcultly. During the bigger modification course,the materials generate laceration and become crack source.(9) The plastic property of wire body which was got by multiple extruding forming was provided during the wire-drawing process.Under the same technological conditions,the phenomenon of broken-wire was dramaticly declined. From the observation of microsructure we find that: the particle size of second-phase SnO₂ was obscure changed after multiple extruding, but it has effected the distributing of the particles obviously;Multiple extruding can relief banded structure ,and reduce the nucleation of particles ,and make the distributing of second-phase particle more uniform.During the subsequent wire-drawing process, the stress increasing of second-phase particle nucleation area, which was cause by inhomogeneous deformation, and the falling of integrality material plastic deforming performance ,which was caused by inner crack,were avoided.(10) With the increasing of experiment times, the trend of component in AgSnO₂ surface is that : the composition of Ag content increasing and SnO₂ content decreasing. During electric lifespan experiments ,the surface of AgSnO₂ electrical contact material appear characteristic DC electric corrosion pattern , such as Ag enrichment zone, SnO₂ enri chment zone, cavity and air hole, crack etc..(11) Effected by arc, SnO₂ particle were blew from arcing zone together with melt Ag at the same time, a spot of SnO₂ particle sublimated by high temperature. The loss of Ag and SnO₂ causes inactivation of contactor material by deformation of surface structure of contactor and deterioration of contact condition.