Microstructure And Properties Of ZL205A Alloy Fabricated By Wire Arc Additive Manufacturing

Aluminum alloy has the advantages of light weight,high specific strength,good ductility and corrosion resistance.Among them,Al-Cu alloys have widely used in aerospace and transportation fields,owing to their high strength and toughness at high temperature.Compared with the traditional subtractive manufacturing process,the wire arc additive manufacturing（WAAM）technology can greatly shorten the preparation time,reduce cost,and obtain materials with complex structure.However,there are some problems in WAAM alloys,such as pores,uneven microstructure and properties,which need to be solved urgently.Al-5.0Cu-0.5Mn-0.25Zr-0.3Ti-0.2Cd-0.2V alloy（ZL205A）was taken as the research object in this paper.The microstructure and properties evolution of wire arc additive manufacturing process and heat treatment were investigated.The main results are as follows:（1）The evolution of microstructure and properties of WAAM-ZL205A alloy during casting,homogenization,extrusion and drawing were studied.The as-cast alloy mainly includedα-Al andθ-Al₂Cu phases.The grains of the alloy were composed of dendritic crystals and equiaxed crystals,and the average grain size was 50.4μm.After homogenization treatment at 510°C,the distribution ofθphase at the grain boundary changed from net-shaped to discontinuous structure.The yield strength and tensile strength decreased from 148.3 MPa and220.1 MPa to 121.6 MPa and 204.7 MPa,respectively,but the elongation increased from 5.1%to 5.8%.After extrusion,the grains of the alloy were elongated along the extrusion direction.The average grain size was 4.7μm×3.5μm（length×width）.Due to the fine grain strengthening mechanism,the yield strength and tensile strength of the alloy increased to 187.2 MPa and 261.1 MPa,respectively,and the elongation was 20.5%.The surface of welding wire was cleanly without oxides.The white Al₂Cu phase in Al matrix distributed along the drawing direction,most of which were oval.（2）The evolution of microstructure and mechanical properties of WAAM-ZL205A alloy were studied.Compared with the bottom and top of the sample,the porosity in the middle of the deposition wall had small pore size and small number,and the relative density reached 92.6%.The microstructure of the alloy was alternating distribution of fine and coarse grain regions,and the second phase mainly includedθ-Al₂Cu andθ′-Al₂Cu phases.Due to the influence of thermal cycle in the forming process,the volume fraction of needle-like metastableθ′phase precipitated in the bottom region was larger than that in the top region.The microhardness of the whole alloy wall were 74.6-84.5 HV,the tensile strength of the middle part of the deposition wall was 255.8 MPa,and the elongation was 15.9%.The properties approached to the as-extruded alloy,which was significantly higher than that of the as-cast alloy.The mechanical properties of WAAM alloy had little anisotropy,and the fracture mode was ductile fracture.（3）The effect of heat treatment on microstructure and mechanical properties of WAAM-ZL205A alloy were investigated.After peak aging treatment at 160°C/14 h,175°C/10 h and 190°C/8 h,the yield strength,tensile strength and elongation of the alloy were 342.7 MPa,447.3 MPa and 12.1%,366.9 MPa,452.1 MPa,12.9%and 383.5 MPa,453.5 MPa,8.1%,respectively.After two-stage aging treatment,theθ′′andθ′precipitates in the alloy coarsened and the volume fraction decreased,the yield strength and tensile strength the alloy were 334.2 MPa,444.2 MPa,respectively.However,the elongation remained unchanged compared with the original WAAM alloy,which was 16.5%.（4）With WAAM-ZL205A alloy after peak aging at 175°C for the research object,the evolution of microstructure and mechanical properties of the alloy after high-temperature thermal exposure were discussed,and the high-temperature mechanical properties were tested.After thermal exposure at 200°C,250°C and 300°C for 6-120 h,theθ′′andθ′phases in the alloy grow up obviously,resulted in the decrease of strength and plasticity.After thermal exposure to 720 h,theθ′′andθ′phases in the alloy grow further,and the strength of the alloy decreased slightly,but the elongation decreased greatly.After thermal exposure at300°C for 720 h,the yield strength,tensile strength and elongation of the alloy decreased to 165.1 MPa,278.5 MPa and 8.9%,respectively.High temperature tensile test at 100-350°C showed that with the increase of tensile temperature,the strength of the alloy decreased gradually,and the elongation increased slightly below 150°C,but decreased gradually above 150°C.The yield strength,tensile strength and elongation of the alloy at 300°C were 87.2 MPa,116.9 MPa and 9.9%,respectively.59 figures,7 tables,101 references...