High Temperature Creep Behavior And Selective Laser Melting Of Al-Cu-Mg-Ag Alloy

Al-Cu-Mg-Ag aluminum alloy is widely used in aerospace and defense industries for its excellent heat resistance and mechanical properties.However,with the continuous development of aerospace,higher requirements on high temperature performance and manufacturing technology of alloy parts are put forward.In this dissertation,high temperature creep behavior and SLM forming of Al-Cu-Mg-Ag alloy were studied by high temperature creep test,SLM forming test,metallographic microscopic analysis,scanning electron microscope,transmission electron microscope and electron backscatter diffraction analysis.The conclusions are as follows:（1）The creep mechanism of the peak-aged Al-Cu-Mg-Ag alloy at170℃、200 MPa～300 MPa is dislocation slip.The steady creep constitutive equation of the alloy is （?）=e^-69.44σ^8.99.The creep fracture characteristics of the alloy under 200 MPa～300 MPa are all ductile dimple transgranular fracture.The relationship between the creep life and the experimental stress is linear in the logarithmic coordinate system,and the average error between the fitting results and the experimental results is8.88%.It can be estimated thatσ₁₀₅¹⁷⁰=143 MPa.（2）The top surface roughness of Al-Cu-Mg-Ag alloy formed by SLM decreases with increasing laser power and decreasing scanning speed.With the increase of laser energy density E,the relative density of the alloy increases first and then decreases,reaching the maximum value of 99.37%with E=44.9 J/mm³.The lack-of-fusion defects decrease with the increase of E,and the lack-of-fusion defects disappear when E exceeds 43.9J/mm³.When E≥53.7 J/mm³,the pore defects begin to appear in the alloy and increase gradually with the increase of E.The length and number of cracks gradually decrease with the increase of E,but even the E reaches 83.3 J/mm³,there are still a certain amount of cracks in the alloy,indicating that the alloy has a high crack sensitivity.（3）The phase composition of Al-Cu-Mg-Ag alloy formed by SLM is mainlyα-Al and Al₂Cu phases.Al₂Cu is distributed on the molten pool boundary in a network shape,with a continuous linear distribution above the pool boundary and a point-like distribution below the pool boundary.With the increase of scanning speed,the solid solubility of alloying elements inα-Al increases gradually,and the spacing between Al₂Cu phases decreases.With the laser energy density decreases from 83.33J/mm³ to 37.17 J/mm³,the average grain size decreases from 28.69μm to13.92μm,and the number of equiaxed grains increases obviously.During SLM process,θ’andΩphases are precipitated in the alloy,showing the characteristics of Al-Cu-Mg-Ag alloy in early aging stage.