Microstructure And Mechanical Properties Of Aluminum Silicon Alloy Containing Cerium

Al-Si alloy has excellent properties,mechanical properties and corrosion resistance.Therefore,Al-Si alloy has a wide range of applications in aerospace,automobile manufacturing and other fields.As a casting alloy,its internal structure defects inevitably occur during the casting process,and theα-Al and eutectic silicon structures in the alloy are relatively coarse,which directly affects the mechanical properties of the alloy.By means of heat treatment,alloying and other methods,the microstructure and grain of the alloy can be effectively refined and the mechanical properties can be improved.At present,rare earth Ce is added to Al-Si alloy as a modifier,and the refinement and modification effect is excellent.However,the influence mechanism of rare earth Ce as a modifier on the microstructure ofα-Al and eutectic silicon in Al-Si alloy and the existence form of rare earth element Ce are still controversial and need to be studied.In this paper,Al-Si alloys with different Ce contents were studied to explore the existence form and mechanism of rare earth element Ce in the alloy,and to study the effect of rare earth element content on the microstructure and mechanical properties of Al-Si alloys.In this paper,Al-Si alloy is taken as the research object,and the rare earth element Ce is added to make the Ce content in the alloy reach 0.1%,0.2%,0.3%,0.5%and 0.8%respectively.The microstructure of the alloy is characterized by metallographic microscope（OM）,scanning electron microscope（SEM）,energy dispersive spectrometer（EDS）,transmission electron microscope（TEM）,X-ray diffraction（XRD）and other equipment,and the hardness and tensile strength of the alloy are tested.The effect of the content of rare earth element Ce on the alloy was studied,and the existence form and mechanism of rare earth element Ce in the alloy were further studied to improve the heat treatment process of the alloy.The results show that:After adding rare earth element Ce,theα-Al of the alloy is refined.During the solidification process of the alloy,the rare earth element Ce will enrich in the front of the solid-liquid interface and hinder the grain growth.At the same time,the Al Ce Si₂ phase formed by Ce,Al and Si in the alloy can be used as the heterogeneous nucleation point of the alloy,which increases the effective nucleation rate of the alloy,so it will refine theα-Al of the alloy.With the increase of rare earth content,excessive Ce will combine to form intermetallic compounds and reduce the refinement effect.Therefore,theα-Al of the alloy shows a trend of decreasing first and then increasing.When the content of rare earth elements is 0.3%,the refinement effect is the best,and the average size ofα-Al is reduced from 80.59μm to 47.93μm.After the addition of Ce,the eutectic reaction supercooling degree of the alloy increases,and the eutectic Si is refined.At the same time,Ce will also modify the eutectic Si in the alloy,and the morphological characteristics change from lath to granular.When the content of rare earth element Ce is 0.3%,the size is the smallest.The morphology of the Fe-rich phase in the alloy also changed.The addition of Ce inhibited the growth of the Fe phase.The size of the long needle-likeβ-Fe phase in the alloy decreased and became thicker and shorter,and the separation of the matrix was reduced.Reduce the negative impact on the alloy.When the alloy is subjected to external force,the crack is more difficult to initiate,and the homogenized structure makes the crack difficult to expand.Therefore,the mechanical properties of the alloy are improved.The hardness of the alloy is increased from65.38 HV to 78.24 HV,and the tensile strength is also increased from 155 MPa to 179 MPa.The best solid solution process of the alloy is 535°C+6 h.The hardness of the alloy with rare earth Ce is increased from 78.24 HV to 86 HV,the tensile strength reaches 237.5MPa,which is increased by 58.5 MPa,and the elongation is 8.21%.In the process of solid solution,theπ-Fe phase transforms to theβ-Fe phase,but its morphology does not change,so it has no adverse effect on the mechanical properties of the alloy.The best aging process of T6 alloy is 160°C+14.5 h.After aging,the mechanical properties are greatly improved.The highest hardness of T6 alloy is 120.6 HV,and the tensile strength reaches 308 MPa,which is 39 MPa higher than that of the alloy without Ce addition.The elongation is 7.02%.The mechanical properties of T6 alloy increase first and then decrease with the increase of rare earth element Ce.