Studies On Preparation And High-temperature Deformation Of Ultrafine-grained Cu-Cr-Zr Alloy

Cu-Cr-Zr is an alloy under ageing treatment with high strength, high thermal andhigh conductive. Cu-Cr-Zr alloy has been widely used in many fields like machinery,national defense and electronic because of its comprehensive properties. Cu-Cr-Zralloy is a new high-strength material which meet the needs and development ofindustrial, compared with conventional Cu-Cr-Zr alloy, Ultra-Fine grained (UFG)Cu-Cr-Zr alloy have a better mechanical properties. This paper have some researchwith UFG Cu-Cr-Zr which made by ECAP in its made, high-temperature tensile andfatigue with Instron8801tensile fatigue testing machine, OM, SEM, TEM and otheranalysis and observation methods.This paper combined ECAP and aging treatment with two different processingand made UFG Cu-Cr-Zr alloy. The alloys forming a uniform equiaxed structure after8passes extrusion by ECAP and the grain of it was refine obviously whose sizes was200nm. ECAP combined with heat treatment can significantly improve the mechanicalproperties and electrical conductivity of the alloys. After8passes extrusion by ECAPand3h aging treatment on420℃, The hardness, tensile strength, elongation andconductivity reached249.15HV,623.1MPa,12.3％and85.34％IACS. Alloys obtainfine dispersed precipitates, which make a contribution to enhance the performance ofthe alloy by its pinning effect to dislocation.After high-temperature tensile on200℃~600℃, we found that on the sametemperature, alloy aging treated exceed8Bc+aging have the higher tensile strength,the elongation were all lower than aging treated exceed4Bc+aging+4Bc except600℃. The former have a larger change on400℃, the tensile strength was65.2MPa andelongation was162.04%on600℃; The latter have a larger change on300℃, thetensile strength was only59.12MPa and elongation was145%on600℃. The tensilefracture characteristics of Cu-Cr-Zr alloy on different temperature after8Bc+agingwas similar with4Bc+aging+4Bc which are different shades of dimples. The dimpledensity was low except600℃which was higher than4Bc+aging+4Bc. When thetemperature reached600℃, fracture showing a lot of equiaxed dimples, new smalldimple show on dimple inner wall.After8Bc+aging, the fatigue performance of Cu-Cr-Zr alloys under differenttemperature were researched. With the stress amplitude rises, week fatigue fractureunder different test temperature alloys are in decline, and with the test temperatureincreases, fatigue limit of the alloy after the first increase and then decrease when300℃get the maximum that is241.49MPa which improve the fatigue limit of28.6%overthe alloy at room temperature. Fatigue limit of the alloy get a larger decline at400℃which decreased by25%compared to room temperature and41.6%compared to300℃. Observing the fracture morphology under the range of36MPa~360MPa stress atdifferent temperatures under cyclic fatigue loading conditions we found that as thetemperature increasing, fatigue crack growth area be smaller, when temperature up to400℃, there is no crack propagation area. Alloy microstructure fracture were dimplegrew up along the stretching direction stretch with the temperature rises and moreevenly distributed, hole was deepening, new small dimple appear in dimple inner wall,plasticity characteristics was significantly. When the temperature is300℃, presents alarge shear lip fracture perpendicular to the loading direction, the reason is microcracksgradually expanded since the crack source.