Study On Precipitation Mechanism Of Ni-Rich Phase In Cu-Ni-Si-Mg Alloy By Phase Field Method

As Cu-Ni-Si-Mg alloy is an age-hardening alloy,the precipitated phase is a key factor affecting the main properties of the alloy such as strength and conductivity.However,the microstructure changes during the aging process of Cu-Ni-Si-Mg alloy are not very clear,and the phase-field study of the precipitated phase of the alloy is relatively small.With the development of the times,only relying on experimental methods can no longer meet the research requirements,and further in-depth research with the aid of simulation is needed.At present,there are not many real material system research cases in simulation research,and most of them are aimed at binary and ternary alloy systems.For this,the use of the phase-field method to simulate multi-element alloy systems still has a certain innovative significance.In this paper,a phase-field model of Cu-Ni-Si-Mg quaternary alloy is established to simulate the growth mechanism of precipitates during the aging of Cu-Ni-Si-Mg quaternary alloy.When the effect of elastic strain energy is completely ignored,the Cu-Ni-Si-Mg alloy undergoes amplitude modulation decomposition very quickly in the early stage of aging at723 K,and the resulting microstructure is composed of two phases of Cu-rich and Ni-rich,Sirich phases.The Cu-Ni-Si-Mg alloy microstructure shows obvious orientation characteristics when considering the effect of elastic strain energy,arranged in the direction of [10] and [01],showing Long rods that are perpendicular to each other.The effect of temperature on the precipitation of Ni-rich phase is attributed to the size and number of precipitated particles,because aging at higher temperatures will produce coarser and fewer particles,and with the increase of temperature(and duration),alloying elements The number density in the Cu matrix is reduced.Through the contribution of these factors,compared with the lower aging temperature,the total volume of the precipitated particles is reduced,and to a certain extent,the precipitation kinetics is reduced.The proper content of Mg promotes the precipitation of solid solution elements and increases the density of the precipitates,thereby inhibiting the growth of the Ni-rich phase,making the particles finer and improving the properties of the alloy.The evolution of the precipitation of different Mg components shows that the addition of Mg increases the density of the precipitates and reduces the spacing between the precipitates,resulting in the interconnection of adjacent Ni-rich phases,making the number density of the precipitated phases increase first and then slowly decrease.Cu-Ni-Si-Mg alloy three-dimensional simulation of Ni-rich precipitation phase change law is basically similar to the two-dimensional situation.Elemental mapping microscopic analysis shows that the precipitated fine particles are related to Cu,Ni,and Si elements,but not to Mg.The simulation results of Cu-Ni-Si-Mg are consistent with the dark-field micrographs in the experiment,and the simulation results are reliable and effective.The complex process performance results show that the hardness(254.8HV),tensile strength(714.6MPa),elongation(14.0%),and electrical conductivity(43.57%IACS)of the alloy achieve a good combination after aging at 450°C for 45 min.