Study On Al-Cu Alloy And Composites Fabricated By Wire Additive Manufactyring

With the rapid development of aerospace,national defense and other fields,the demand for large,light and high strength complex structural parts is increasing day by day.Due to the advantages of high deposition rates,high material utilization rate and low equipment costs,wire+arc additive manufacturing(WAAM)has been deemed as a promising additive manufacturing technology in producing large-scale metal parts.Aluminum and its alloys are widely used in WAAM to meet the requirements of aerospace and defense industries because of their outstanding physical properties,such as low density,excellent corrosion resistance,good mechanical properties,high thermal conductivity etc.However,in the aluminum alloys structural parts fabricated by WAAM,the defects such as microstructure inhomogeneity,coarse microstructures and gas porosity hinder the improvement of mechanical properties.To solve these problems existing in WAAM aluminum alloy parts,Al-Cu alloy wall was successfully built through WAAM.The microstructure evolution and mechanical properties along the height direction were studied.The results showed that the average grain size of the samples was 26.1～40.1μm from the bottom to the top,and the average grain size was very different.Moreover,the microhardness and tensile strength of the as deposited WAAM Al-Cu alloy reduced from the bottom to the top due to the intrinsic heat treatment,which resulted in partial aging and non-uniform formation of intermetallic compounds along the building direction.Heat treatment was carried out on WAAM Al-Cu alloy to improve microstructure inhomogeneity.After heat treatment,the average grain size was 37.2～44.3μm from the bottom to the top.The difference between different parts in the WAAM samples was small and the microstructure became homogeneous.However,the grains grow up after heat treatment,which is not conducive to the improvement of mechanical properties of materials.TiB2 particles can inhibit dendrite growth,refine grains and reduce the hot cracking tendency of Al-Cu alloys.Therefore,Ti B2 particles reinforced Al-Cu composite wall was successfully built through WAAM.The average grain size of the as-deposited sample was 8.3μm,which was significantly lower than that of the as-cast Ti B2/Al-Cu composite(27.3μm).However,the introduction of Ti B2 particles increases the viscosity of liquid metal and hinters the discharge of gas,resulting in the number and size of pores in the WAAM composite samples larger than WAAM alloy parts,which seriously affects mechanical properties.In order to control and even eliminate the pores in WAAM Ti B2/Al-Cu composite,Ti B2/Al-Cu composite was fabricated by electron beam free form fabrication(EBF~3).The density of as-deposited EBF~3 Ti B2/Al-Cu composite was up to99.89%,which was 0.98%higher than the sample of as-deposited WAAM Ti B2/Al-Cu composite.The hardness of the T6-treated EBF~3 Ti B2/Al-Cu composite was 153.8 HV.The yield strength and ultimate tensile strength in the horizontal direction was 305 MPa and 343 MPa,respectively,which were 124 MPa and 108 MPa higher than the yield strength and tensile strength of WAAM Ti B2/Al-Cu composite samples.