由于7075铝合金主要组成元素的沸点较低、熔体的表面张力梯度较大,加之定向能量沉积(DED)工艺中常用的圆形高斯分布(CG)激光束斑能量分布的不均匀性,导致7075铝合金DED试样的成形质量普遍不佳,这极大限制了7075铝合金DED的进一步应用.通过激光光场模式调控,可以有效改变熔池的温度场、流场及其相应的凝固条件,从而提升激光增材制造试件的成形质量和微观组织的主动控制能力.采用离轴抛物积分镜将CG光场模式匀化为圆形平顶分布(CF)光场模式,并进一步将CF光场模式倾斜以获得横向椭圆平顶分布(TE)光场模式.利用这三种不同的光场模式激光分别制备了7075铝合金DED的单道熔覆、单壁墙及块体试样.结合数值模拟,揭示光场模式对成形质量及凝固组织的影响规律及其内在机理.模拟结果显示,将激光束斑从传统的CG光场模式调制为CF与TE光场模式后,激光在熔覆层表面的热通量均匀性得到显著改善,进而减小了熔体温度梯度,提高了凝固速率.与CG光场模式相比,成形质量方面,CF与TE光场模式下单壁墙和块体试样的表面成形质量得到显著提升,其中单壁墙的宽度变化大幅降低,块体试样水平方向的尺寸精度提高,此外块体试样的致密度分别从95.8%提升至97.2%与97.7%;凝固组织方面,织构得到显著弱化,并且晶粒尺寸减小约50%,同时晶粒内纳米析出相η相的数量也有所增加.
Due to the low boiling points of the main constituents of 7075 aluminum alloy and the high surface tension gradient of the molten alloy,combined with the uneven energy distribution of the circular Gaussian(CG)laser beam spot commonly used in directed energy deposition(DED)processes,the forming quality of 7075 aluminum alloy DED specimens is generally poor.This significantly restricts the further application of DED in 7075 aluminum alloy.By regulating the laser mode,it is possible to effectively modify the temperature and flow fields of the melt pool,as well as the corresponding solidification conditions.Thus,the forming quality of laser additive manufacturing specimens and the active control of microstructure are improved.An off-axis parabolic integrating mirror is employed to homogenize the CG laser mode into a circular flat-top(CF)laser mode,which is further tilted to achieve a transversely elliptical flat-top(TE)laser mode.Using these three different laser modes,single-track cladding,single-wall structures,and 7075 aluminum alloy in DED block specimens are prepared.Combined with numerical simulations,the influence laws and underlying mechanisms of the laser modes on the forming quality and solidification structure are revealed.The simulation results indicate that by modulating the laser beam spot from the conventional CG laser mode to the CF and TE laser modes,the uniformity of the heat flux on the surface of the cladding layer is significantly improved,subsequently reducing the temperature gradient of the melt,and increasing the solidification rate.Compared to the CG laser mode,the surface forming quality of single-wall structures and block specimens under the CF and TE laser modes is significantly enhanced.The width variation of the single-wall structures is greatly reduced,and the dimensional accuracy in the horizontal direction of the block specimens is improved.Additionally,the density of the block specimens increases from 95.8%to 97.2%and 97.7%,respectively.In terms of solidification structure,the texture is significantly weakened,the grain size is reduced by approximately 50%,and the number of nano-precipitated η-phase within the grains is also increased.
史东来;贾车旺;孙刘铄;赵宇凡;杨海欧;林鑫
西北工业大学 凝固技术国家重点实验室,西安 710072||西北工业大学 金属高性能增材制造与创新设计工业和信息化部重点实验室,西安 710072
金属材料
定向能量沉积;高强铝合金;光场模式调控;成形质量;微观组织
directional energy deposition;high-strength aluminum alloy;laser mode control;forming quality;microstructure
《材料工程》 2024 (007)
44-56 / 13
陕西省自然科学基础研究计划青年项目(2022JQ-479)
10.11868/j.issn.1001-4381.2024.000121
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