| Additive manufacturing technologies such as laser melting deposition have the advantages of no mold,high design freedom,and short production cycle.They are especially suitable for the preparation of small batches and complex components in the field of rail transportation and aerospace.However,the aluminum alloy has low laser absorption rate,easy oxidation,and problems such as pore defects during the deposition process,which limits the engineering application of this material.In this paper,the main research object of aluminum-silicon eutectic alloy is to study the formation process of pore defects during the laser melting deposition process,and the process and mechanism of ultrasonic degassing and remelting degassing are analyzed.The effect of ultrasonic vibration,remelting and its composite technology on the structure and mechanical properties of the laser melting deposition samples were discussed.The ultrasonic-assisted laser remelting test piece was compared with the traditional casting specimen to verify the ultrasonic-assisted laser melting Feasibility of depositing and preparing high-performance aluminum alloy components.The main results are as follows:There are two kinds of defects,lack of fusion and porosity in the Al-12 Si alloy laser melt deposition layer.By adjusting the laser power,scanning speed,scanning distance and other parameters,unfused defects can be eliminated,however,there are still about 4.6% of pores remaining.The pores are mainly hydrogen pores,most of which are derived from metal powder.The laser porosity of the deposited layer and the application of ultrasonic vibration can effectively reduce the porosity.The main degassing mechanism prolongs the existence of the molten pool for the remelting process.The cavitation of ultrasonic waves and the effect of acoustic flow accelerate the escape of gas.Under the laser power 1 100 W,scanning speed 6 mm/s,scanning distance 1 mm,remelting power 1 100 W,ultrasonic power 1 000 W ultrasonic assisted laser remelting composite process,the maximum density of 99.1% deposition test specimens can be obtained.The microstructure and mechanical properties of Al-12 Si samples obtained from four main laser deposition processes(laser melting deposition,ultrasonic assisted laser melting deposition,laser remelting,and ultrasonic assisted laser remelting)were analyzed.It can be seen that the microstructure of the deposited layer is mainly composed of aluminum solid solution and aluminum-silicon eutectic,which is macroscopically anisotropic.Compared with the laser melting deposition process,the average density of ultrasonic assisted laser remelting is increased from 95.4 ± 0.4% to 98.2 ± 0.9%,and the average grain size of ?-Al is refined from 71.8 ?m to 19.4 ?m.The elongation increased by 17% and 53% respectively.The grain refinement of ?-Al is mainly due to the nucleation proliferation and dendrite fragmentation of ultrasonic waves,while the increase in density is the result of the combined action of ultrasonic waves and remelting.Compared with the traditional casting method,the aluminum-silicon eutectic alloy produced by ultrasonic assisted laser remelting has similar composition and density.Due to the rapid cooling characteristics of the laser and the cavitation and acoustic flow effects of ultrasonic waves,the size of ?-Al dendrites The range is refined from 15-540 ?m of cast samples to 7.5-97.5 ?m,and the volume fraction of aluminum solid solution is increased from 11-16% to 45-55%.The silicon particles are also refined from 5.6-32.1 ?m in the as-cast state to below 2 ?m.The change in microstructure also brings about an improvement in mechanical properties.Compared with the traditional casting method,the microhardness of the ultrasonic-assisted laser remelting deposition method is significantly improved,and the tensile strength,yield strength and elongation can reach 107 ± 4 MPa,227± 3 MPa,12.2% ± 1.4%,which is 51%,38% and 56% higher than the corresponding tensile propserties of castings. |
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