Study On The Aging Hardening Behavior Of Au-20Ag-10Cu-(1-3)Ni Quaternary Alloy

Pure gold has low and stable resistance,good conduction,thermal conductivity and chemical stability.However,lower hardness and strength limit its application.In this thesis,1%and 3%Ni were added to the basis of the Au-20Ag-10Cu alloy.Adding Ni can improved the strength and hardness of gold alloy as well as its mechanical and electrical properties.It can also be used to prepare excellent electrical contact materials.In this thesis,Au-20Ag-10Cu-?1-3?Ni allys were prepared by vacuum induction.By means of DSC,OM,XRD,TEM,tensile property test,microhardness,test,resistivity,fracture morphology observation,we studied the changing rule of microstructure,phase transition and properties for the alloy in the process of different heat treatment.We obtained following results:?1?Au-20Ag-10Cu-?1-3?Ni alloy had excellent results of solid solution strengthening,and its strength and hardness were improved.After solid solution treatment,the hardness of Au-20Ag-10Cu,Au-20Ag-10Cu-1Ni and Au-20Ag-10Cu-3Ni alloy reached 152HV,163HV,194HV respectively and the strength of them reached475MPa,638MPa and 732MPa respectively.?2?After aging treatment of different temperature,different time and different deformation,it had obvious effect of aging hardening.For these alloys with solid solution-aging treatment,the hardness of Au-20Ag-10Cu,Au-20Ag-10Cu-1Ni and Au-20Ag-10Cu-3Ni alloys were 266HV,235HV and 218HV when the temperature was250?.The intensity of them were 679MPa,873MPa,866MPa respectively.when the temperature was 350?,the hardness of alloys were 251HV,275HV,285HV.The strength was 697MPa,1014MPa,1069MPa.After the alloy rolling-aging treatment,the hardness of the alloys is greatly improved on the basis of rolling state,and the effect of aging hardening is remarkable.After rolling 90%,the hardness reached the highest aging at 350?,306HV,334HV and 359HV respectively.?3?After the deformation reaching 90%,work hardening was obvious.and the microhardness of these alloy increased to 266HV,276HV,281HV respectively.After drawling the deformation 89.6%,the alloy strength was 940MPa,972MPa,1053MPa.After the rolling deformation and annealing treatment,the microhardness of the alloy first rises and then decreases,and finally becomes balanced.The addition of Ni increased the recrystallization temperature of the alloy by 50?.?4?The alloy was solid solution a₀ phase by solid solution treatment.When the temperature reached 145?,alloy occur solid solution state ordered phase?₀ phase?AuCuI;When the temperature reached 307?,the?₁ phase of the alloy began to precipitate and the solid solution?₀ phase?AuCuI+rich silver?₁ phase.The precipitation of the ordered phase increases the hardness and strength of the alloy,while the lattice constant and the resistivity of the alloy decrease.?5?The addition of 1%and 3%Ni can improve the strength,microhardness and the resistivity of alloy and can refine grain of alloy.In conclusion,Au-20Ag-10Cu-?1-3?Ni alloy has excellent effect of solid solution strengthening,work hardening,aging strengthening,and all three kinds of strengthening methods can greatly improve the strength and hardness of the alloy and improve the resistivity of the alloy.