Development And Application Research Of In-Situ Al₂O₃ Phase Aluminum Alloy Powder Core Wire By Cylindrical Lattice Wire Arc Additive Manufacturing

The aluminum alloy three-dimensional lattice structure with good thermal insulation and load-bearing properties is an important part of the thermal protection system of hypersonic aircraft.Wire arc additive manufacturing has the advantages of high forming efficiency and low cost,which is an effective new method to fabricate aluminum alloy lattice structure.However,the thermal insulation performance of wire arc additive manufacturing lattice structure using the existing aluminum alloy wire is low,and the forming process of wire arc additive manufacturing curved lattice structure is lacking,so it is difficult to fabricate a lattice structure that meets the requirements of use.To this end,this paper developed a special in-situ Al₂O₃ phase aluminum alloy powder core wire for wire arc additive manufacturing,studied and fabricated a cylindrical aluminum alloy lattice structure with good thermal insulation and load-bearing properties.The following research results are obtained:The Al-Cu-Ni O alloy system of in-situ Al₂O₃ phase aluminum alloy powder core wire was established.During the process of wire arc additive manufacturing,Al₂O₃ phase was formed by substitution reaction between Al and Ni O.The developed in-situ Al₂O₃phase aluminum alloy powder core wire had a stable droplet transfer process,good arc stability,a spatter rate of less than 0.8%in the lattice unit rod wire arc additive manufacturing process,and the surface roughness of the formed unit rod did not exceed 11μm.The relationship between wire arc additive manufacturing process parameters of the developed in-situ Al₂O₃ phase powder cored wire and the size of the lattice unit rods was studied.When the wire feeding speed was within 3～7 m/min,the number of cold metal transfer（CMT）cycles was within 1～5,and the offset of the arc gun was within 0～0.5 mm,the lattice unit rod with a diameter of 2.20～5.02 mm and an inclination angle of 30°～90°could be accurately formed.The effect of Ni O content in the powder core wire on the microstructure and properties of the unit rod was analyzed.The increase of Ni O content in the powder core increased the in-situ Al₂O₃ phase in the unit rod,which promoted the grain refinement of the unit rod,produced the second phase strengthening,and improved the strength of the unit rod.Meanwhile,the thermal conduction mechanism of in-situ Al₂O₃phase is not coordinated with that of the aluminum matrix,which leads to heat loss,and the grain refinement increases the number of grain boundaries,which leads to the increase of heat transfer distance,and reduces the thermal conductivity of the unit rod.The process parameters of double-stage aging heat treatment for lattice unit rod were optimized.The final process parameters were optimized as follows:primary aging temperature 105℃,primary aging time 10 h,secondary aging temperature 200℃,secondary aging time 22 h.The double-stage aging heat treatment promoted the precipitation of the Al₂Cu second phase in the unit rod,and improved its second phase strengthening effect.The forming path of cylindrical pyramid lattice structure was obtained by cylindrical slicing,a 2-layer pyramid lattice structure containing 300 unit cells was fabricated by wire arc additive manufacturing on a cylindrical surface using the developed in-situ Al₂O₃phase aluminum alloy powder core wire.The in-situ Al₂O₃ phase effectively improved the heat insulation and bearing capacity of the cylindrical lattice structure.