Study On Additive Manufacturing Aluminum Alloy Under The Influence Of Environmental Factors

Laser additive manufacturing（LAM）technology using metal powder as raw material and laser as heat source has become one of the hot directions in the field of additive manufacturing technology research and engineering application.Based on laser heat source and metal powder,LAM technology mainly includes two types:selectively laser melting（SLM）technology with pre-spread powder and direct metal deposition（DMD）technology with synchronous powder feeding.LAM technology can achieve efficient forming of complex components,and has important application prospects in the manufacturing of high-performance and difficult-to-process aluminum alloy components.The performance of the formed parts is closely related to the process parameters and powder quality,and the storage environment is an important factor affecting powder quality.This paper takes offshore 3D printing as the background and simulates the storage of powder under temperature and humidity conditions to explore the influence of storage conditions on the performance of Al Si10Mg specimens formed by LAM.The main research contents are as follows:Firstly,the influence of environmental factors on the properties of Al Si10Mg powder was investigated.The temperature and humidity of the environment can affect the physical and chemical properties of the powder.With the increase of temperature and humidity,the surface morphology,loose packing density,moisture content,and powder flowability of the powder all decreased to varying degrees.However,the powder properties could be restored to their original state after drying,indicating that water molecules were adsorbed onto the surface of the powder in a physical form.The phase distribution and basic elements did not change,and the Hydrogen element came from the water molecules attached to the surface of the powder,which significantly decreased after drying.The Oxygen element content was related to storage time and temperature and would not decrease due to drying.Subsequently,the influence of environmental factors on the properties of Al Si10Mg alloy formed by SLM was investigated.Through 25 groups of orthogonal experiments,the effect of laser energy density（LED）on the density and hardness of Al Si10Mg alloy formed by SLM was revealed,and the optimal forming process parameters were determined.The density and hardness of Al Si10Mg alloy formed by SLM increased first and then decreased with the increase of LED,and the optimal LED for Al Si10Mg alloy formed by SLM was in the range of 70-100 J mm^-3.The best process parameters were laser power of 275 W,scanning speed of 1250 mm/s,and scanning distance of 80μm.Based on the optimized parameters,the influence of environmental factors on the properties of Al Si10Mg alloy formed by SLM was studied.The surface morphology,density,hardness,and tensile properties of the powder-formed parts stored in a temperature and humidity environment were significantly reduced.The increase of storage temperature promoted the absorption of water molecules and oxidation reaction by the powder,resulting in further reduction of the properties of the formed parts.The density of the powder stored at50°C80%72h decreased by 1.55%,the hardness decreased by 27.10 HV,and the tensile strength decreased by 97 MPa compared with the original powder.Drying treatment can significantly restore the properties of the formed parts after temperature and humidity treatment,but cannot completely restore them to the original powder state due to the presence of oxides.Finally,the influence of environmental factors on the properties of Al Si10Mg alloy formed by DMD was investigated.The effect of process parameters on the size of a single deposition layer melt pool and micro-hardness was determined through single-factor experiments.The optimal process parameters for a single deposition layer were determined as laser power of 4800 W,scanning speed of 14 mm/s,and powder feeding rate of 24g/min.Based on the optimal parameters for a single deposition layer,the optimal overlay ratio and Z-axis ascent height were determined as 40%and 1.2 mm,respectively,with morphology,surface roughness,and hardness as indicators.The surface morphology,density,hardness,and tensile properties of powder-formed parts stored in a temperature and humidity environment were significantly reduced,and drying treatment can significantly restore the properties of the powder-formed parts after temperature and humidity treatment.The reduction in powder properties during storage in a temperature and humidity environment was related to moisture content and oxidation.An increase in humidity and storage time can promote the absorption of water molecules by the powder,resulting in further reduction of the properties of the formed parts.The density of the powder stored at 30°C80%72h decreased by 0.77%,the hardness decreased by 18.20 HV,and the tensile strength decreased by 38 MPa compared to the original powder.Therefore,the powder should be stored as far away from the external environment as possible,especially in high-temperature and high-humidity environments,and the powder should be dried before forming to significantly improve the properties of the formed parts.