Study On Microstructure And Properties Of High Strength Aluminum Alloy Al7075

Al-Zn-Mg-Cu alloys are widely used in aerospace,transportation,automobile manufacturing,military and other fields because of their low density,high specific strength,good toughness and corrosion resistance.Augmented manufacturing technology can directly manufacture solid parts from three-dimensional digital model,which can make the parts lightweight and composite,save materials,short manufacturing cycle,low cost and so on.Therefore,the manufacture of Al-Zn-Mg-Cu alloys by adding materials has important research significance and good application prospects.The solidification temperature range of Al-Zn-Mg-Cu alloys is small,and the solidification cracking is sensitive,so the application and development of reinforcement manufacturing technology of this kind of alloys is relatively slow.In order to study the feasibility of adding material to Al-Zn-Mg-Cu series alloy,this paper explores and realizes the adding material manufacturing of high strength aluminum alloy Al7075 through two kinds of increasing material manufacturing methods:laser melting deposition and arc fuse.Firstly,7075 aluminum alloy was prepared by laser melting deposition with different laser power.The effects of different laser power on macroscopic morphology,density,microstructure and properties were investigated,and the microstructure characteristics,phase formation and precipitated phase were characterized.Oxidation and powder spheroidization exist in the deposition process,and the deposited sample collapses slightly.When the laser power is 1.1kw,the surface morphology of the deposited sample is smoother.The surface roughness profile is smaller,the density is higher,the tissue stomatal defects are less,and the hardness is the highest.The microstructure evolution of the deposition sample is mainly due to the transformation from columnar crystal to equiaxed crystal,columnar crystal is formed at the bottom and middle,equiaxed crystal is formed at the top,and the microstructure shows typical preferred orientation growth.The phase of the deposited sample is mainly composed of matrix Al phase and precipitated phase,and the shape and size of the precipitated phase are different and the distribution is uneven.The tensile strength of the deposited sample is 158.66 MPA,the yield strength is 122.3 MPA,and the elongation is 2.3%,showing low strength and poor ductility,which is mainly caused by stomatal defects.The fracture morphology shows that the fracture form is mainly brittle fracture and the fracture mechanism is intergranular fracture.Based on the advantages of high deposition rate and high material utilization of WAAM,especially in the manufacture of large-size components,and combined with the characteristics of CMT process in controlling heat input,reducing spatter and refining grains,single-pass multi-layer Al-Zn-Mg-Cu aluminum alloy was prepared by CMT-WAAM deposition system,and its microstructure and mechanical properties were comprehensively analyzed and compared with cast 7075 aluminum alloy.The microstructure of the deposited sample shows a layered distribution of dendrites,equiaxed crystals and a small amount of columnar crystals in the horizontal direction,and the deposition direction is composed of equiaxed crystals and a small amount of slender columnar crystals,showing the characteristics of epitaxial growth.the microstructure of the two orientations is finer than that of cast 7075 aluminum alloy.The average hardness in the horizontal direction is 73.15 HV_0.1,the tensile strength is 358.64 MPa,the yield strength is 196.15 MPa,and the elongation is 37.9%.The average hardness of the deposition direction is 86.06 HV_0.1,the tensile strength is269.29 MPa,the yield strength is 140.65 MPa,and the elongation is 32.52%.Compared with traditional cast 7075 aluminum alloy,the mechanical properties such as hardness,wear resistance and tensile strength are lower,but the corrosion resistance is better.In order to further understand the microstructure evolution characteristics and precipitation phase law of CMT-WAAM deposition,the deposited samples were characterized by EBSD,EMPA and TEM.The results show that the deposited samples have preferred orientation and texture.There is segregation in the element.The solute partition coefficients of the main alloy elements Si and Cu are relatively small,and they are enriched at grain boundaries and dendritic boundaries to form residual second phases.The main shape of the second phase is rod-shaped and oval-shaped.It was identified as Mg₂Si and?(Mg(Zn,Cu,Al)₂)phase by high resolution transmission electron microscopy and energy spectrum analysis.