Study On Microstructure And Properties And Heat Treatment Process Of 2A50 Forged Aluminum Alloy By Laser Melting Deposition

Laser melting deposition technology has attracted more and more attention due to its advantages of preparing gradient materials and composite materials,unlimited forming size,fast forming rate,and being applied to parts repair.However,in terms of laser melting deposition of aluminum alloy,mature materials mainly focus on Al～Si alloy,and the mechanical properties are poor.Forged aluminum alloy is widely used in medium and high strength structural parts,so there is an urgent demand for laser melting deposition process of forged aluminum alloy.In this thesis,the laser melting deposition process of 2A50 forging aluminum alloy is studied as follows:The effects of laser power,scanning mode and powder feeding rate on the densification,microstructure and properties of 2A50 alloy during laser melting deposition were investigated.The process parameters window with excellent properties and easy forming was obtained.The microstructure of 2A50 aluminum alloy single channel sample by laser melting deposition has the characteristics of rapid solidification structure.The microstructure was divided into columnar dendrite region,equiaxed dendrite region and transition region.The main phases wereα～Al,Cu Al₂ and Q phases.The optimal laser melting deposition process of 2A50 forging aluminum alloy was determined as follows:laser power of 3000W,scanning rate of 3mm/s,powder feeding rate of 1.6g/min,scanning mode of bidirectional scanning,laser incidence angle of 8°,carrier gas flow of 3.3L/min,layer thickness of 0.3mm.Under these technological parameters,the average microhardness of the sample was 90.7HV,the tensile strength was207MPa,the yield strength is 85MPa and the elongation was 14%.The influence of heat treatment process parameters on the microstructure and mechanical properties of LMD formed 2A50 alloy was studied,and the optimal heat treatment parameters were obtained.The results show that:the solution effect of the sample solution at 540℃for 1h was the best.With the increase of solution temperature,the effect of second phase dissolving into the matrix became better.When the solution temperature was too high,the second phase cluster appeared,and the dissolution effect became worse.With the increase of aging time,the microstructure of the sample is in turn non-uniform precipitation of second phase,aggravation of inhomogeneity,uniform refinement of microstructure and precipitation of coarse single phase.The best aging time is 16h.The optimum heat treatment process was determined as follows:solution temperature:540℃,solution time:1 hour,water quenching;aging temperature:150℃,aging time:16 hours,air cooling.After three different T6 treatments,the microstructure of the sample changed from columnar crystal to intermittent chain,uniformly distributed spherical second phase and coarse second phase,respectively.After T6 treatment,the second phase transformation occurred,Mg₂Si phase and Al_1.9Cu Mg_4.1Si_3.3 phase appeared;After heat treatment,the average microhardness of the sample increased to more than 120HV,with an increase of 32.2%;After heat treatment,the tensile strength,yield strength and elongation of as deposited samples increased to 321MPa,245MPa and 8%,respectively.