Effect Of Nano Y₂O₃ Particles And Rare Earth Y On The Hot Tearing Susceptibility And Properties Of Aluminum Matrix Composites

Cast Al-Cu alloys are widely used in various important fields because of their high strength,low density,good ductility,and excellent performance at room temperature and high temperature.However,due to the poor casting performance of Al-Cu alloys,serious hot crack defects are likely to occur during solidification,resulting in changes in casting performance.In severe cases,the casting broke due to stress concentration.Therefore,this thesis takes ZL205A alloy with high strength and toughness in Al-Cu system alloy as the basic research object.In experiment,nano-Y₂O₃ reinforced ZL205A composites and Y-3Y₂O₃/ZL205A composites were prepared by external application,respectively.On the one hand,the hot tearing susceptibility of nano particles reinforced aluminum matrix composites was studied.On the other hand,the rare earth Y on the hot tearing susceptibility of 3Y₂O₃/ZL205A composites was also studied.Through the analysis of the grain size and solidification temperature range of the composites with Y₂O₃ particles and rare earth Y added,the relationship between the hot tearing susceptibility of the composites and the grain size and solidification temperature range was clarified.And the effect of rare earth Y on the tensile properties of 3Y₂O₃/ZL205A composites at room temperature and high temperature was explored.Moreover,through the analysis of the structure,fracture morphology and grain boundary phases of the composites after tensile test,the mechanism of the influence of rare earth Y on the mechanical properties of Y₂O₃/ZL205A composite with high content of reinforced particles was revealed.Firstly,the effect of hot tearing susceptibility of ZL205A composites under different Y₂O₃ particle content was studied.The results showed that when 0.2%Y₂O₃particles were added,the grain size of the composites is significantly refined,and the grain size of the matrix ZL205A alloy is reduced from 54.01?m to 34.90?m,which decreased 35.4%.At the same time,the solidification temperature range of the composites is reduced from 108.18?to 103.66?,which decreased 4.2%,and the reduction in the grain size and solidification temperature range was conducive to the reduction of shrinkage strain,and the susceptibility of the composite s to hot tearing is significantly improved.Therefore,the hot tearing susceptibility of composite decreased from 18.57 to 8.94 of the matrix ZL205A alloy,which decrease d 51.8%.When the content of Y₂O₃ particles in the reinforced phase exceeded 0.2%,as the content of Y₂O₃ particles increased,the grain size of the composites remained at about 35.00?m and no longer decreases.And Y₂O₃ particle agglomerates appeared in the composites,which made it difficult for the liquid metal to flow and replenish during the solidification process,caused the shrinkage strain to increase gradually and the hot tearing susceptibility of the composites to increase.At the moment,the effect of rare earth Y on the hot tearing susceptibility of3Y₂O₃/ZL205A composites was studied.The results showed that the aggregates of Y₂O₃ particles in the composites gradually disappeared with the increase of Y content,and the grain structure is significantly refined.The?-Al₂Cu phase,?₁-Al₈Cu₄Y phase,?Al,Cu?₁₁Y₃ phase and Y₂O₃ particles are evenly distributed,the grain boundary bridgings are obviously increased,and the solidification temperature rang is gradually reduced,which promoted the improvement of the hot tearing susceptibility of the composites.The ternary phases of various Al-Cu-Y system formed by rare earth Y and Al and Cu elements in the composites hindered the crack propagation and changed the solidification process,which reduced the solidification temperature range of the composites.When adding rare earth Y of 0.3%,1%and 2%,the hot tearing susceptibility values of the composites decreased from 51.2 of the matrix3Y₂O₃/ZL205A composite to 50.1,31.0 and 19.5,respectively.Therefore,the addition of rare earth Y can significantly improve the hot tearing susceptibility of the composites.Finally,the effect of rare earth Y on the tensile properties of 3Y ₂O₃/ZL205A composites at room temperature and high temperature was studied.The results showed that adding appropriate amount of rare earth Y can significantly improve the tensile strength and elongation of the composites at room temperature and high temperature.When the content of rare earth Y was 0.3%,the tensile strength of the composites at 25?,180?and 230?tensile temperatures were 354 MPa,317 MPa and 305 MPa,respectively.Compared with the 341 MPa,314 MPa and 289 MPa of the matrix 3Y₂O₃/ZL205A composites,it has increased by 3.7%,1.0%and 5.5%.Elongations were 8.4%,6.4%and 7.2%,compared with the 6.7%,4.7%and 5.3%of the matrix 3Y₂O₃/ZL205A composite,it has increased by 25.5%,36.2%and 35.8%,respectively.When the content of rare earth Y was 0.6%,the elongations of composites at 25?,180?and 230?were 10.7%,10.5%and 11.8%respectively.Compared with the matrix 3Y₂O₃/ZL205A composite,it has increased by 59.7%,123.4%and 122.6%,respectively.It can be seen from the above that the addition of rare earth Y helps to improve the composite room temperature and high t emperature tensile properties.