本研究將鈮（Nb）箔材作為改質元素導入雷射箔材列印技術（LFP），於無預熱條件下成功製備無裂紋且高致密度AA6061鋁合金構件。透過分析雷射功率與掃描速度對熔池形貌之影響，並結合機器學習建立製程加工圖，以辨識穩定傳導模式熔融及高致密化成形之較佳製程參數。結果顯示，Nb添加能有效抑制凝固裂紋形成，並使試樣相對密度可達99.9%。
微觀組織方面，XRD結果顯示，Nb添加後α-Al之主要繞射峰由 (200) 轉變為 (111)，且可偵測到對應Al3Nb之 (112) 繞射峰。EBSD 分析進一步顯示，Nb改質AA6061之晶粒尺寸由75.63 μm顯著降低至1.95 μm。HRTEM觀察到奈米級Al3Nb析出物與α-Al 之界面特徵，並透過 d-spacing量測進一步確認Al3Nb析出物之存在，其可作為良好的異質成核核心，促進晶粒細化並降低凝固裂紋形成傾向。
機械性質方面，Nb改質之AA6061展現良好的強度與延展性平衡，其抗拉強度為318 MPa，延伸率為21 %，相較於未改質AA6061分別提升29.2 %及162.5 %。SEM斷口分析觀察到韌窩與撕裂脊等典型延性斷裂特徵，且高倍率SEM影像中則可觀察到直徑約1.9 μm之Al3Nb包晶顆粒。
整體而言，本研究證實Nb添加能有效改善AA6061於LFP製程中之裂紋敏感性、微觀組織與機械性質，展現其作為鋁合金 LFP 成分改質策略之應用潛力。此外，鈮箔材亦可作為合金元素載體，將改質元素直接導入熔池並實現原位成分改質，為高強度鋁合金積層製造提供新的成分設計方向。

In this study, niobium (Nb) foil was used as a modifying element and incorporated into the Laser Foil Printing (LFP) process. Crack-free AA6061 aluminum alloy components with high relative density were successfully fabricated without preheating. The effects of laser power and scanning speed on melt pool morphology were analyzed, and a process map was established with the assistance of machine learning to identify suitable processing parameters for stable conduction-mode melting and high-density fabrication. The results show that Nb addition effectively suppressed the formation of solidification cracking, and the relative density of the specimens reached 99.9%.
In terms of microstructure, the XRD results show that the dominant diffraction peak of α-Al changed from (200) to (111) after Nb addition, and the (112) diffraction peak corresponding to Al3Nb was detected. EBSD analysis further showed that the grain size of Nb-modified AA6061 was significantly reduced from 75.63 μm to 1.95 μm. HRTEM observations revealed nanoscale Al3Nb precipitates and their interfacial features with α-Al. The presence of Al3Nb precipitates was further confirmed by d-spacing measurements, indicating that they can act as effective heterogeneous nucleation sites, promote grain refinement, and reduce the tendency for solidification cracking.
In terms of mechanical properties, the Nb-modified AA6061 exhibited a good balance between strength and ductility, with an ultimate tensile strength of 318 MPa and an elongation of 21%. Compared with unmodified AA6061, these values were increased by 29.2% and 162.5%, respectively. SEM fracture surface analysis showed typical ductile fracture features, including dimples and tearing ridges. In addition, pro-peritectic Al3Nb particles with a diameter of approximately 1.9 μm were observed in the high-magnification SEM images.
Overall, this study shows that Nb addition effectively reduces the cracking susceptibility and improves the microstructure and mechanical properties of AA6061 fabricated by LFP, demonstrating its potential as a compositional modification strategy for aluminum alloy LFP. In addition, Nb foil can serve as an alloying element carrier, allowing the modifying element to be directly introduced into the melt pool and enabling in-situ compositional modification. This provides a new compositional design direction for the additive manufacturing of high-strength aluminum alloys.

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