Study On The Properties Of Cold Spray Additively Manufactured A380 Aluminum Alloys

Cold spray additive manufacturing is an emerging solid state additive manufacturing technology which has attracted great attention due to its multiple advantages over traditional additive manufacturing techniques.These include,non-oxidation,non-phase transition,unlimited size of the prepared material and the ability to repair the unserviceable material during the preparation process.However,the bonding between particles is mainly physical in nature such as mechanical interlocking,which leads to poor interfacial bonding of the particles and high density of internal defects.Therefore,the mechanical properties of materials are poor,which limits the widespread application of cold spraying additive manufacturing.This thesis focuses on improving the mechanical properties of bulk materials prepared by cold spray additive manufacturing.A commonly used aluminum-silicon alloy A380 powder was selected as the raw material and the bulk materials were prepared by cold spray additive manufacturing.Further,we systematically studied the effects of ’heat treatment’,’hot rolling’ and ’addition of hard phase to the feedstock’ on the microstructure and mechanical properties of materials.Finally,effective methods for improving the mechanical properties of materials were proposed.In the first phase of this project,the effects of post spray heat treatment on the properties of sprayed A3 80 samples were systematically studied.The as-sprayed A380 bulk material exhibited very low strength and brittle fracture behavior.Results showed that an appropriate heat treatment can eliminate the work hardening in the as sprayed material,improve the interfacial bonding and eliminate the micropores with limited improvement in the mechanical properties.The mechanical properties of the annealed material still showed a significant gap with that of the cast A380 material which limits its use for industrial applications.It was concluded that a single heat treatment can not significantly change the deformation behavior of the deposited particles to heal out the high density of pores formed at the inter-particle boundaries.In the second phase of this project,the effect of post spray hot rolling treatment on microstructure and mechanical properties of cold spray additively manufactured A380 materials was studied.The results showed that the A3 80 interparticle bonding completely became a metallurgical bonding in nature during the hot rolling process and the Si particles reinforced composite is formed in situ.The strength and plasticity of the rolled material were about twice as high as that of the casting material,which meets the application requirements.This method is simple,economical and easy to operate.However,it has a limitation on the shape of the material as it is only applicable for the post-treatment of cold spray additively manufactured tubues or plates.In the final phase of this work,addition of Al2O3 particles to the feedstock and post-spray annealing co-treatments were identified for cold spray additively manufactured components with arbitrary geometry to achieve dense microstructure and excellent properties.In order to determine the specific addition scheme of Al2O3 particles in the feedstock,we systematically studied the effects of different morphologies and contents of Al2O3 particles on the microstructure of the deposits.The results showed that spherical Al2O3 particles exhibited micro-tamping effect during the deposition process.During spraying,spherical Al2O3 particles impacted the surface of the deposited layer and forced the particles to undergo secondary plastic deformation,thereby reducing the density of internal defects in the material.Deposits containing spherical Al2O3 particles exhibited low porosity,very low retained Al2O3 content,low surface roughness,and good coating/substrate interfacial bonding.The optimum content of spherical Al2O3 in the feedstock was 20 wt%when it was used as a micro-tamping agent.The irregular Al2O3 particles mainly showed the embedding effect during cold spray process with high deposition efficiency.The hardness values of the deposits containing irregular Al2O3 particles were higher than those of deposits containing spherical Al2O3 particles.However,Al2O3 particles retained in the deposits were easy to break,thus resulting in high porosity and low coating/matrix interfacial bonding.Based on the above findings,we fabricated a dense A3 80 bulk material through cold spraying using the original A380 powder containing 20 wt.%spherical Al2O3 particles.Then the material was subjected to subsequent annealing heat treatment.It was found that annealing results in aggregation of micropores at the particle boundaries,fusion of the particle interface,recovery and re-crystallization phenomena.Consequently,the mechanical properties of the final material exceeded those of the cast homogeneous A380 alloy thereby meeting the application standards.Further,we studied the comprehensive properties of bulk materials prepared by adding heterogeneous Al2O3 particles(spherical+irregular)to the original A380 feedstock powder.The results showed that through a comprehensive control over the tamping and embedding effect of Al2O3 particles,the mechanical properties of the material cannot be lower than that of the cast material while its wear resistance is excellent.This results in is a multi-performance integrated material with broad application prospects.