Deformation Aging Behavior Of Powder Metallurgy Cu-Cr-Mg Alloy

Cu-Cr based alloys are widely used in the communication industry,high-speed train catenary lines,and electric vehicles,due to their excellent mechanical properties and high electrical conductivities.However,the Cr precipitate in Cu-Cr alloys is prone to coarsening,stemming from high diffusion velocity of Cr element in Cu matrix and easy-activated recrystallization behavior.By alloying the Mg element,the mechanical properties of the Cu-Cr alloy had shown effective and distinct improvement,ascribed to the restrained growth of precipitates and delayed recrystallization behavior by segregating Mg element along the interface between matrix and precipitates.Cu-Cr-Mg alloys were generally prepared by casting method.This method,results in macro-segregation,pore inclusions,and coarse dendrite structures,etc.These defects were generally difficult to be eliminated,leading to serious weakening for both mechanical and electrical performances of final products.In this work,Cu-0.28Cr-0.19Mg(wt.%)alloy prepared by powder metallurgy(PM)were generally characterized by fewer defects as well as more homogenized microstructure and showed high performance-price ratio when producing complex components.The effects of cold rolling(CR)deformation and aging process on its microstructure and properties were systematically studied,and the strengthening mechanism and phase transformation kinetics were calculated and analyzed.The main conclusions can be obtained as follows:1.After 950°C solid-solution treatment for 4h + cold rolling by 80% +450 °C aging for 1h,the PM Cu-0.28Cr-0.19 Mg alloy had excellent combination of mechanical properties and electrical conductivity,and its tensile strength,yield strength,fracture strain and conductivity were 674.4MPa,545.8 MPa,12.9% and 85.5% IACS,respectively.2.The strengthening mechanism of the CR80 PM Cu-0.28Cr-0.19 Mg alloy under peaking aging were mainly precipitation strengthening,dislocation strengthening and grain boundary strengthening,and calculated to be approximately 43.7,24.5,and 23.1% of yield strength,respectively.The grain boundary strengthening is the main reason why present PM Cu-Cr-Mg alloy exhibits enhanced strength,which is 325%higher than the corresponding cast Cu-Cr-Mg alloys.3.The calculated diffusion activation energies of CR50,CR70,and CR80Cu-0.28Cr-0.19 Mg alloy were about 151.2 ± 19.8 k J/ mol,141.8 ± 20.2k J/mol,and 126.7 ± 15.7 k J/mol,respectively.The gradually decreased activation energy of PM Cu-Cr-Mg alloy with increasing reduction rate suggests that deformation is helpful in accelerating the precipitation.