As-Cast Microstructure of Cu-1Cr-0.1Zr Alloy with or without La Addition
With the advent of the era of integration and informatization,integrated circuits and chips are rapidly advancing with a broader range of applications.The demand for lead frame materials used in integrated circuits is steadily rising,the Cu-Cr-Zr alloy is gaining increasing attraction used in lead frame due to the good balance of high tensile strength and high electrical conductivity,it is widely regarded as one of the most promising alloys for meeting the demands of lead frame materials.However,the tensile strength of Cu-Cr-Zr alloy have not yet to meet the high-performance demand,further improvement is needed.Microalloying is a highly effective method for enhancing the mechanical properties of alloys.Furthermore,the addition of rare earth elements to alloys can purify the ma-trix,remove impurities,and facilitate degassing,which leading to high electrical conductivity,these effects are more pronounced in the as-cast state of the alloy.La is a light rare earth element,and its price is relatively affordable,it has a wide range of applications,including its use in piezoelectric materials,electric heating materials,thermoelectric materials,magnetic resistance materials,lumi-nescent materials(lanthanum phosphors),hydrogen storage materials,optical glass,laser materials,various alloy materials,and more.In Cu-Cr-Zr alloys,the densities of Cr and Zr are lower than that of Cu,making them easily suspended on the surface of the Cu liquid during alloy melting.Additionally,Zr and La elements are highly susceptible to burning loss during this process.Based on this,the ingots of Cu-1Cr-0.1Zr and Cu-1Cr-0.1Zr-0.14La were prepared by vacuum induction melting in this paper.The macrostructure of the as-cast alloys was observed by optical microscope(OM),and the morphology and evolution of the primary phase were observed by field emission-scan electroscope microscope(SEM)with energy dispersive X-ray spectrometry(EDS)detector and high-resolution transmission electron microscopy(TEM).From OM images,it could be concluded that the addition of La could obviously refine the grain that from columnar crystal to equiaxed crystal.Moreover,the addition of La could mitigate effectively the dendrites segregation,promote the refinement and dispersion of network eutectic structure of chromium(Cr)phase,and rare earth of La element mainly dis-tributed at the interdendritic interface.When the rare earth element La was added,due to its limited solubility in Cu,a significant number of La atoms accumulated at the solid-liquid interface during the solidification process.This led to a reduction in the interfacial free energy,which hindered the advancement of the interface and restricted the ability of Cr atoms at the interface to diffuse further,consequently suppressing dendrite growth.TEM images showed that Zr enriched on Cr phase surface,inhibited Cr phase growth and made Cr phase spherical.However,after the addition of La,the combination of La and Zr weakened the spheroidization effect of Zr on Cr phase,resulting in rod-like Cr phase along the<110>Cu,which mainly related to the value of the elastic strain energy ΔE and the in-terface energy σ,In addition,there was a perfect coherent relationship between the rod-like precipitates and copper matrix,it also found two set of the diffraction spots in the diffraction pattern,the faint diffraction spots showed the cube-on-cube orientation relation-ship(OR)with Cu matrix.SEM results provided further validation that the addition of La could effectively mitigate dendrite segrega-tion,promoting the refinement and dispersion of the network eutectic structure,and the size of the precipitated phase were measured.EDS results confirmed the composition of the phase.In the as-cast alloy,the main phases presented in Cu-1Cr-0.1Zr alloy were:a retic-ular eutectic Cr phase,spherical Cr phase with the size of about 3 μm,and elliptical Cu5Zr phase with dimensions of approximately 6μm.However,after the addition of 0.14％La,the as-cast alloy mainly consisted of a reticular eutectic Cr phase,rod-like Cr phase,rod-like ternary CuCrZr phase with dimensions ranging from 4 to 10 μm,and La-rich phase.This study provided a comprehensive character-ization and systematic analysis of the microstructures of as-cast Cu-1Cr-0.1Zr and Cu-1Cr-0.1Zr-0.14La alloys,from macroscopic to mi-croscopic scales.The addition of La indeed had a significant impact on the precipitated phases and the eutectic phases in the as-cast al-loy,the changes in the microstructure of ingots were bound to affect the performance in as-cast alloy and subsequent processing perfor-mance.It was predicted that the addition of La could enhance the strength of Cu-Cr-Zr alloy while maintaining a relatively high level of electrical conductivity,which would drive the development of lead frame materials and provide valuable guidance for further research.
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