Abboud Jaafar, Mazumder Jyoti
Department of Automobile, College of Engineering of Al-Musayab, University of Babylon, Hillah, Iraq.
Center for Laser Aided Intelligent Manufacturing, Department of Mechanical Engineering, University of Michigan, 2350 Hayward St, Ann Arbor, MI, 48109, USA.
Sci Rep. 2020 Jul 21;10(1):12090. doi: 10.1038/s41598-020-69072-1.
Laser surface melting followed by rapid solidification is an effective means to produce very fine microstructures with desirable surface properties because of the high rates of cooling associated with it. In the present study, the effect of rapid cooling on the silicon particle size, distribution, and morphology of hypereutectic Al-17wt.%Si and Al-20wt.%Si alloys have been investigated. A continuous-wave CO2 laser of wavelength 10.6 μm and a Trumpf Yb-YAG disk laser of wavelength 1.030 μm were used with a beam diameter of 1 mm and scanning speeds ranging from 5 to 100 mm/s. Rapid solidification increased the solubility of silicon in aluminum to approximately 5wt% and induced non-equilibrium hypoeutectic microstructures comprising large volume fractions of primary α-Al dendrites and ultrafine Al-Si eutectic of lamellar morphology. Both α-Al dendrites and the silicon particle sizes were significantly reduced from micron to nanoscale level. The morphology of silicon particles is modified from massive polygonal and plate-like to a mixture of fine flakes with round corners, feathery and fibrous, or a coral-like and thread-like structure. The eutectic silicon size and the interlamellar spacing were reduced to 30 and 10 nm, respectively. Furthermore, most of the silicon crystals in the eutectic region and the aluminum dendrites contained a significant number of twins which were considered as an essential contributor to the mechanism of growth and branching. Microhardness values increased two to threefold due to the refinement of the microstructural constituent.
激光表面熔化随后快速凝固是一种有效的手段，由于与之相关的高冷却速率，能够产生具有理想表面性能的非常精细的微观结构。在本研究中，研究了快速冷却对过共晶Al-17wt.%Si和Al-20wt.%Si合金中硅颗粒尺寸、分布和形态的影响。使用了波长为10.6μm的连续波CO2激光器和波长为1.030μm的Trumpf Yb-YAG盘式激光器，光束直径为1mm，扫描速度范围为5至100mm/s。快速凝固使硅在铝中的溶解度增加到约5wt%，并诱导出非平衡亚共晶微观结构，该结构包含大量初生α-Al枝晶和层状形态的超细Al-Si共晶。α-Al枝晶和硅颗粒尺寸都从微米级显著减小到纳米级。硅颗粒的形态从块状多边形和板状转变为带有圆角的细薄片、羽毛状和纤维状的混合物，或珊瑚状和丝状结构。共晶硅尺寸和层间距分别减小到30和10nm。此外，共晶区域和铝枝晶中的大多数硅晶体都含有大量孪晶，这些孪晶被认为是生长和分支机制的重要贡献者。由于微观结构成分的细化，显微硬度值增加了两到三倍。
