The Interaction between Grains during Columnar-to-Equiaxed Transition in Laser Welding: A Phase-Field Study

A phase-field model was applied to study CET (columnar-to-equiaxed transition) during laser welding of an Al-Cu model alloy. A parametric study was performed to investigate the effects of nucleation undercooling for the equiaxed grains, nucleation density and location of the first nucleation seed ahead of the columnar front on the microstructure of the fusion zone. The numerical results indicated that nucleation undercooling significantly influenced the occurrence and the time of CET. Nucleation density affected the occurrence of CET and the size of equiaxed grains. The dendrite growth behavior was analyzed to reveal the mechanism of the CET. The interactions between different grains were studied. Once the seeds ahead of the columnar dendrites nucleated and grew, the columnar dendrite tip velocity began to fluctuate around a value. It did not decrease until the columnar dendrite got rather close to the equiaxed grains. The undercooling and solute segregation profile evolutions of the columnar dendrite tip with the CET and without the CET had no significant difference before the CET occurred. Mechanical blocking was the major blocking mechanism for the CET. The equiaxed grains formed first were larger than the equiaxed grains formed later due to the decreasing of undercooling. The size of equiaxed grain decreased from fusion line to center line. The numerical results were basically consistent with the experimental results obtained by laser welding of a 2A12 Al-alloy.

[1]  X. Shao,et al.  Identification of nucleation mechanism in laser welds of aluminum alloy , 2019, Applied Physics A.

[2]  Mark F. Horstemeyer,et al.  Insight into the mechanisms of columnar to equiaxed grain transition during metallic additive manufacturing , 2019, Additive Manufacturing.

[3]  Li Feng,et al.  Phase-field simulation of competitive growth of grains in a binary alloy during directional solidification , 2018, China Foundry.

[4]  Jincheng Wang,et al.  Non-uniplanar competitive growth of columnar dendritic grains during directional solidification in quasi-2D and 3D configurations , 2018, Materials & Design.

[5]  Z. Wang,et al.  Investigation on evolution mechanisms of site-specific grain structures during metal additive manufacturing , 2018, Journal of Materials Processing Technology.

[6]  D. Gu,et al.  Modeling and simulation of the columnar-to-equiaxed transition during laser melting deposition of Invar alloy , 2018, Journal of Alloys and Compounds.

[7]  S. Felicelli,et al.  Three-Dimensional Lattice Boltzmann Modeling of Dendritic Solidification under Forced and Natural Convection , 2017 .

[8]  Y. Shibuta,et al.  Multi-GPUs parallel computation of dendrite growth in forced convection using the phase-field-lattice Boltzmann model , 2017 .

[9]  Yiyi Li,et al.  Multi-scale Simulation for the Columnar to Equiaxed Transition in the Weld Pool , 2016 .

[10]  Lei Wang,et al.  A phase field investigation of dendrite morphology and solute distributions under transient conditions in an Al–Cu welding molten pool , 2016 .

[11]  L. Nastac.  An Efficient 3D Stochastic Model for Predicting the Columnar-to-Equiaxed Transition in Alloy 718 , 2015 .

[12]  Qingyan Xu,et al.  A Modified Cellular Automaton Model for the Quantitative Prediction of Equiaxed and Columnar Dendritic Growth , 2014 .

[13]  Wenjian Zheng,et al.  Onset of the initial instability during the solidification of welding pool of aluminum alloy under transient conditions , 2014 .

[14]  J. Deschamps,et al.  Directional solidification of inclined structures in thin samples , 2014 .

[15]  B. Nestler,et al.  A phase-field study of large-scale dendrite fragmentation in Al-Cu , 2012 .

[16]  N. Provatas,et al.  Microstructure analysis of AZ31 magnesium alloy welds using phase-field models , 2012 .

[17]  A. Viardin,et al.  Phase-field modeling of the columnar-to-equiaxed transition in neopentylglycol-camphor alloy solidification , 2011 .

[18]  M. Martorano,et al.  Mechanical Blocking Mechanism for the Columnar to Equiaxed Transition , 2008 .

[19]  Jincheng Wang,et al.  Phase-field simulation of microstructure development involving nucleation and crystallographic orientations in alloy solidification , 2007 .

[20]  J. Baruchel,et al.  In-Situ and Real-Time Investigation of Columnar-to-Equiaxed Transition in Metallic Alloy , 2007 .

[21]  J. A. Spittle.  Columnar to equiaxed grain transition in as solidified alloys , 2006 .

[22]  C. Beckermann,et al.  Phase-field simulation of the columnar-to-equiaxed transition in alloy solidification , 2006 .

[23]  Peter D. Lee,et al.  Simulation of the columnar-to-equiaxed transition in directionally solidified Al-Cu alloys , 2005 .

[24]  Marcelo de Aquino Martorano,et al.  A solutal interaction mechanism for the columnar-to-equiaxed transition in alloy solidification , 2003 .

[25]  C. Gandin,et al.  Experimental Study of the Transition from Constrained to Unconstrained Growth during Directional Solidification , 2000 .

[26]  R. Trivedi,et al.  Nucleation ahead of the advancing interface in directional solidification , 1997 .

[27]  H. W. Kerr,et al.  The effect of alloy composition and welding conditions on columnar-equiaxed transitions in ferritic stainless steel gas-tungsten arc welds , 1990 .

[28]  J. Hunt,et al.  Steady state columnar and equiaxed growth of dendrites and eutectic , 1984 .

[29]  Y. Shibuta,et al.  Large–scale phase–field lattice Boltzmann study on the effects of natural convection on dendrite morphology formed during directional solidification of a binary alloy , 2020 .