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激光功率对激光粉末床熔融成形Fe–Mn–Al–Ni–C轻质钢组织及性能的影响

Effect of laser power on microstructure and properties of Fe–Mn–Al–Ni–C lightweight steels prepared by laser powder bed fusion

    摘要
  • 摘要: 设计了Fe–30Mn–11Al–12Ni–1C轻质合金钢成分，研究了激光功率对激光粉末床熔融成形轻质钢组织及性能的影响。结果表明，在扫描速度一定的情况下，随着激光功率的增加，激光粉末床熔融成形轻质钢试样的相对密度逐渐增大，激光功率在120 W时，成形样品相对密度最高，达到99.2%。不同激光功率下成形试样在平行于构筑方向的平面（XOY）上均出现未熔合区域，垂直于构筑方向的平面（XOZ）出现裂纹。XOY观察面与XOZ观察面的缺陷类型不同，体现在以下方面：XOY面存在大量未熔合孔隙、球状粉末以及较大的孔洞，且随着激光功率的增加，未熔合的缺陷和孔洞面积逐渐减少，球状粉末消失；XOZ面缺陷主要是孔洞和裂纹，随着激光功率的上升，孔洞逐渐减少，但裂纹宽度增加。试样硬度呈现出各向异性，且各向异性随着激光功率的提高逐渐减小。试样XOZ面硬度随激光功率的变化不明显，但高于XOY面；XOY面由于激光功率提高降低了缺陷的影响，因此显微硬度变化较大。当激光功率为120 W时，试样XOZ面硬度达到最大值HV0.2 441.3。激光功率90 W、扫描速度800 mm·s−1，成形的轻质钢试样抗拉强度达到最大值，为826.2 MPa。试样晶界处存在大量析出相，导致其延伸率较低，因此激光粉末床熔融成形轻质钢的塑性较差。

     

    Abstract: The composition of Fe–30Mn–11Al–12Ni–1C lightweight alloy steels was designed and the effect of laser power on the microstructure and properties of the lightweight steels formed by laser powder bed fusion (LPBF) was studied in this paper. The results show that the relative density of lightweight steel samples formed by LPBF increases gradually with the increase of laser power at a constant scanning speed, and the relative density of samples formed at 120 W is the highest, reaching 99.2%. Under the different laser power, the unfused regions appear in the plane parallel to the construction direction (XOY), and the cracks appear in the plane perpendicular to the construction direction (XOZ). The defect types on the XOY observation plane are different from the XOZ observation plane, which are reflected in the following aspects: XOY plane has a large number of unfused pores, spherical powders, and large holes, and with the increase of laser power, the unfused defects and hole areas gradually decrease, and the spherical powders disappear; the defects on the XOZ plane are mainly holes and cracks, with the increase of laser power, the holes decrease gradually, but the crack width increases. The hardness of samples shows anisotropy, and the anisotropy gradually decreases with the increase of laser power. The hardness on the XOZ plane does not change obviously with laser power, but it is higher than the XOY plane. The microhardness on the XOY plane changes greatly, because the laser power increases and the effect of defects is reduced. When the laser power is 120 W, the hardness on the XOZ plane reaches the maximum as HV0.2 441.3. With laser power of 90 W and scanning speed of 800 mm·s−1, the yield strength and tensile strength of the formed light steel samples reach the maximum value, which are 800.8 MPa and 825.4 MPa respectively. There is a large amount of the precipitated phase at the grain boundary of the samples, resulting in the low elongation of all the samples, so the plasticity of the LPBF formed light steel is poor.

     

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