Microstructure And Mechanical Properties Control Of CMT Arc Additively Manufactured 2319 Aluminum Alloy

2219 aluminum alloy belongs to 2XXX（Al-Cu）alloy,which is characterized by high strength,so it is usually called hard aluminum alloy.It is widely used in aerospace rocket welding oxidizer tank and fuel tank in aviation and aerospace fields,supersonic aircraft structural materials.ER2319 aluminum alloy is specially used for welding Al-Cu alloy electrode and filler solder,its composition is the same as 2219 aluminum alloy.Benefit from the wide application field of 2219 aluminum alloy,its additive manufacturing technology has become a research hotspot.However,if the mainstream laser additive manufacturing technology is adopted,the aluminum alloy will have spheroidal crystallization due to high reflectivity,resulting in poor metallurgical bonding.Using arc as the heat source avoids the problem of high reflectivity and the arc additive manufacturing has high forming efficiency,which has obvious advantages in the field of aluminum alloy manufacturing.CMT technology is a new type of welding process with small heat input and less spatter.It is very suitable for the additive manufacturing of low melting point metals such as aluminum alloys.In this paper,after completing the forming process research and characterization of microstructure and performance of 2319aluminum alloy manufactured by CMT arc additive manufacturing,the microstructure evolution rule is initially revealed.Formulating heat treatment process suitable for the as-deposited 2319 aluminum alloy,optimizing precipitation strengthening effect to achieve peak aging.Ultrasonic vibration is introduced to refine the grains and control pore defects,thereby improving the mechanical properties of the as-deposited 2319 aluminum alloy and making its comprehensive mechanical properties close to traditional manufacturing methods.The main research contents and results are as follows:The microstructure of the as-deposited 2319 aluminum alloy is non-uniformly distributed,a large number of dendrites are distributed in the top arc area,and intermittent distribution of point-like and rod-like eutectic structures（α-Al+Cu Al₂）.The dendrites in the middle and lower melt-stable region gradually transition to equiaxed grains,the network eutectic structure is continuously distributed,and there are a few columnar grains in the bottom region.The structure characteristics of different regions of the as-deposited2319 aluminum alloy are different,but they show a regular grain morphology evolution process,forming a uniform growth of the grain along the direction of the deposition height.The Cu element is dissolved in the Al matrix or exists in the form of Cu Al₂,and the microstructure difference of the alloy is small under different forming parameters.In this state,the tensile properties of the as-deposited 2319 aluminum alloy are not anisotropic,the tensile strength and yield strength can reach 277MPa and 119MPa,respectively,and the elongation is about 13%.A large number of equiaxed dimples are distributed on the tensile fracture,and the fracture mechanism is ductile fracture.The heat treatment process of the as-deposited 2319 aluminum alloy was studied.The results show that the hardness and strength of the as-deposited 2319 aluminum alloy after heat treatment（solid solution:535℃,60min+aging:175℃,3h）are significantly improved.By analyzing the key factors to realize the heat treatment structure and performance optimization,the process adaptability of the Retrogression and re-ageing treatment to the as-deposited 2319 aluminum alloy was explored.The key structural characteristics that affect the strength of the alloy are clarified,and the aging peak point of the alloy under the condition of retrogression and re-ageing treatment is explored.The results show that there are a large number of dispersedθ″and isolatedθ’phases in the alloy matrix at 11 h,and the width of the PFZ is narrow,which makes the strength of the alloy peak.The tensile strength and yield strength reached 394MPa and 266MPa,respectively,and the elongation was 8.1%.Therefore,the combined heat treatment system of solution aging treatment and retrogression and re-ageing treatment can make the comprehensive mechanical properties of the as-deposited 2319 aluminum alloy better than the 2219T4 deformed aluminum alloy,which is close to 2219T6 deformed aluminum alloy.After the introduction of ultrasonic vibration,the grain refinement of the as-deposited 2319 aluminum alloy is obvious,and the average grain diameter is reduced from 147.20μm to 71.06μm,which is 48%finer.A large number of coarse columnar grains distributed in the deposited state are suppressed after the introduction of ultrasonic vibration,the microstructure is composed of fine equiaxed grains and equiaxed dendrites,and the uniformity of the microstructure is improved.In addition,ultrasonic vibration has a good degassing effect,which can effectively reduce the number of pores of the as-deposited 2319 aluminum alloy and reduce the average diameter of the pores.After the introduction of ultrasonic vibration,the number of pores can be reduced by 79%,basically eliminating the pores above 70μm.In terms of mechanical properties,after the introduction of ultrasonic vibration,the tensile strength and yield strength of the 2319aluminum alloy were slightly increased,which were 3.4%and 6%higher than the deposited state.The elongation decreased slightly.The isotropic characteristics of tensile properties are more pronounced.