Study on Microstructure and Mechanical Properties of 2A50-T6 Aviation Aluminum Alloy Repaired by Laser Cladding
Objective Aluminum alloy offers the advantages of light weight,high specific strength,and good corrosion resistance,and is widely used in the manufacture of aviation components.Laser remanufacturing technology serves as an effective method to reduce costs and increase efficiency for repairing irregular gaps in key aircraft parts such as fuel tanks,electric boxes,and wall panels caused by clamping,collision,and machining errors.Compared to surfacing welding,thermal spraying,and plasma spraying,laser cladding offers higher energy density,lower heat input,and greater flexibility,giving it a broad future prospect.Currently,pore defects are a primary issue in the laser cladding repair of aluminum alloys.Scholars are actively studying the impact of laser process parameters on porosity and mechanical properties,as well as the formation mechanisms and influencing factors of pores and other defects within the cladding.However,it remains crucial to continue exploring process parameters to achieve better samples.The effects of porosity and microstructure on mechanical properties also require further investigation.In this study,AlSi10Mg powder is used to repair 2A50-T6 aluminum alloy by laser cladding.The research focuses on how laser process parameters affect the porosity,microstructure,and mechanical properties of the cladding layer,uncovers the formation mechanism of pore defects,and establishes the relationship among density,tensile strength,and elongation.Methods The repaired substrate material is 2A50-T6 aluminum alloy,measuring 75 mm×55 mm×5 mm.The surface has a trapezoidal groove processed into it,with the upper and lower bottoms measuring 10 mm and 6 mm,respectively,a depth of 2 mm,and an opening angle of 120°.The repair powder used is AlSi10Mg powder with a particle size of 50-150 μm.For the laser cladding repair,a 6-kW laser and a six-axis robot are employed.The repair method adopts a multi-layer and multi-channel approach,with a scanning speed of12mm/s,a powder feeding rate of0.8g/min,a spot diameter of 1.6 mm,a bonding rate of 40％,and laser powers of 1400,1600,1800,and 2000 W.After the repair,metallographic samples are prepared.The weld morphology and porosity are analyzed,and the mechanical properties are evaluated.A scanning electron microscope(SEM)with an energy dispersive spectrometer(EDS)is used to observe the microstructure of the coated sample.The content and distribution of alloying elements are determined by EDS.The phase of the repaired area is analyzed by X-ray diffraction(XRD),the porosity is calculated using ImageJ,and the microhardness of samples is measured by a microhardness tester.The tensile properties of the samples are measured by a universal tensile testing machine,and the fracture morphology is observed by SEM.Results and Discussions After laser deposition,the repaired area exhibits a fish-scale structure(Fig.3).With increasing power,the density also increases,and the density of the repaired area can reach 99.96％at 2000 W.The main phases in the repaired area are α-Al and Mg2Si(Fig.5).The solubility of Mg in the matrix increases with the increase of laser power,enhancing the effect of solid solution strengthening.The central zone of the fuse is dominated by equiaxed crystals,and the interlaminar binding zone is dominated by columnar crystals(Fig.6).The pore defects in the repaired area are mainly manifested as process pores and metallurgical pores(Fig.8).Specifically,process pores are mainly caused by cavities produced by vaporization injection of low-melting metal at high laser power(Fig.9).Furthermore,metallurgical pores are caused by changes in the solubility of hydrogen during the cladding process(Fig.10).The 2000 W sample exhibits the highest tensile strength of 283.278 Mpa and the highest elongation of 4.017％(Table 3 and Fig.11).With the increase in density,the tensile strength and elongation of the sample exhibit a similar increasing trend(Fig.12).The observation and analysis of the fracture morphology of the tensile specimen show that with the increase of power,the size and number of dimples also increase,the depth is deeper,and the toughness improves(Fig.13).According to the hardness test,the hardness of the base material is high,the hardness of the repaired area is low,there is a relatively obvious softening phenomenon near the heat-affected zone,and the hardness drops sharply in the pores(Fig.14).The average hardness of the restoration zone under 2000 W is 88.26 HV,which is much higher than that under 1400 W,73.88 HV.Pore defects are the main reason for the decrease of hardness in the low-power restoration zone.Conclusions The aforementioned analysis shows that as laser power increases,the density of the sample increases.Furthermore,the density of the repaired area of the sample can reach 99.96％at a laser power of 2000 W,and the pore characteristics are mainly metallurgical pores and process pores.The repaired area is mainly α-Al and Al-Si eutectic,and it contains a small amount of Mg2Si enhanced phase.The microstructure mainly exhibits equiaxed crystals in the center of fuse and columnar crystals between layers.Among samples at the four types of power,the sample at 2000 W exhibits the optimal mechanical properties.The tensile strength is 283.278 Mpa,reaching 93.185％strength of the matrix,and the elongation is 4.017％,reaching 52.101％elongation of the matrix.The increase in tensile strength and elongation of the sample exhibits the same trend as the increase in density.The hardness of the repaired area also increases with an increase in laser power,and no obvious softening phenomenon is observed at 2000 W.Additionally,the pore defect at low power is the main factor for the reduction in hardness.
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