Due to the low content of alloying elements and the lack of effective nucleation sites,the fusion zone(FZ)of tungsten inert gas(TIG)welded AZ31 alloy typically exhibits undesirable coarse columnar grains,which can res...Due to the low content of alloying elements and the lack of effective nucleation sites,the fusion zone(FZ)of tungsten inert gas(TIG)welded AZ31 alloy typically exhibits undesirable coarse columnar grains,which can result in solidification defects and reduced mechanical properties.In this work,a novel welding wire containing MgO particles has been developed to promote columnar-to-equiaxed transition(CET)in the FZ of TIG-welded AZ31 alloy.The results show the achievement of a fully equiaxed grain structure in the FZ,with a significant 71.9%reduction in grain size to 41 μm from the original coarse columnar dendrites.Furthermore,the combination of using MgO-containing welding wire and pulse current can further refine the grain size to 25.6 μm.Microstructural analyses reveal the homogeneous distribution of MgO particles in the FZ.The application of pulse current results in an increase in the number density of MgO(1-2 μm)from 5.16 × 10^(4) m^(-3) to 6.18 × 10^(4) m^(-3).The good crystallographic matching relationship between MgO and α-Mg matrix,characterized by the orientation relationship of[11(2)0]α-Mg//[0(1)1]MgO and(0002)_(α-Mg)//(111)_(MgO),indicates that the MgO particles can act as effective nucleation sites for α-Mg to reduce nucleation undercooling.According to the Hunt criteria,the critical temperature gradient for CET is greatly enhanced due to the significantly increased number density of MgO nucleation sites.In addition,the correlation with the thermal simulation results reveals a transition in the solidification conditions within the welding pool from the columnar grain zone to the equiaxed grain zone in the CET map,leading to the realization of CET.The exceptional grain refinement has contributed to a simultaneous improvement in the strength and plasticity of welded joints.This study presents a novel strategy for controlling equiaxed microstructure and optimizing mechanical properties in fusion welding or wire and arc additive manufacturing of Mg alloy components.展开更多
During the tungsten inert gas(TIG)welding process of Ti_(2)AlNb alloy,high heat input leads to the formation of coarse grains,which are detrimental to the mechanical properties of welded joints.To address this problem...During the tungsten inert gas(TIG)welding process of Ti_(2)AlNb alloy,high heat input leads to the formation of coarse grains,which are detrimental to the mechanical properties of welded joints.To address this problem,Ta microalloyed welding wires were developed to enhance the strength of the welded joints.The Ta-modifed fusion zone(FZ)exhibited a well-defned structure with a smooth,defect-free surface.Systematic analysis of the microstructure evolution and mechanical properties of the welded joints revealed that the Ta element completely dissolves into the FZ.During solidifcation,a signifcant constitutional undercooling efect occurs,promoting the columnar-to-equiaxed transition(CET)and reducing grain size from 187.42 to 133.49μm.Mechanical properties tests indicated that with increased Ta content,the strength of the welded joints initially increased and then decreased.When the Ta content in the welding wire was 1 wt%,the joints showed the best performance,with a tensile strength of 909.36 MPa and an elongation of 1.21%.Compared to the welded samples without Ta,the tensile strength and elongation increased by 153.01 MPa and 0.53%,respectively.Grain refnement and increased dislocation density were the main reasons for the improved mechanical properties.However,excessive Ta content led to signifcant the intragrain misorientation,increasing the joint’s anisotropy and causing uneven deformation during tensile testing.Therefore,further addition of Ta did not substantially enhance the tensile properties of the joint.Additionally,the paper provides a detailed analysis of the low elongation observed in the joint.After welding,dislocations were neatly arranged in the FZ,forming numerous parallel dislocation walls,leading to local stress concentration and accelerating crack initiation and propagation.Consequently,the elongation at the weld was lower than that of the base metal(BM).This research ofers a new approach to improve the mechanical properties of Ti2AlNb alloy during welding.展开更多
The effect of addition temperature of MgO particles(MgOp)on their dispersion behavior and the efficiency of grain refinement in AZ31 Mg alloy was investigated.In addition,the grain refinement mechanism was systematica...The effect of addition temperature of MgO particles(MgOp)on their dispersion behavior and the efficiency of grain refinement in AZ31 Mg alloy was investigated.In addition,the grain refinement mechanism was systematically studied by microstructure characterization,thermodynamic calculation,and analysis of solidification curves.The results show that the grain size of AZ31 Mg alloy initially decreases and then increases as the MgOp addition temperature is increased from 720 to 810℃,exhibiting a minimum value of 136μm at 780℃.The improved grain refinement efficiency with increasing MgOp addition temperature can be attributed to the reduced Mg melt viscosity and enhanced wettability between MgOp and Mg melt.Furthermore,a corresponding physical model describing the solidification behavior and grain refinement mechanism was proposed.展开更多
基金supported by the National Natural Science Foundation of China(No.51871155).
文摘Due to the low content of alloying elements and the lack of effective nucleation sites,the fusion zone(FZ)of tungsten inert gas(TIG)welded AZ31 alloy typically exhibits undesirable coarse columnar grains,which can result in solidification defects and reduced mechanical properties.In this work,a novel welding wire containing MgO particles has been developed to promote columnar-to-equiaxed transition(CET)in the FZ of TIG-welded AZ31 alloy.The results show the achievement of a fully equiaxed grain structure in the FZ,with a significant 71.9%reduction in grain size to 41 μm from the original coarse columnar dendrites.Furthermore,the combination of using MgO-containing welding wire and pulse current can further refine the grain size to 25.6 μm.Microstructural analyses reveal the homogeneous distribution of MgO particles in the FZ.The application of pulse current results in an increase in the number density of MgO(1-2 μm)from 5.16 × 10^(4) m^(-3) to 6.18 × 10^(4) m^(-3).The good crystallographic matching relationship between MgO and α-Mg matrix,characterized by the orientation relationship of[11(2)0]α-Mg//[0(1)1]MgO and(0002)_(α-Mg)//(111)_(MgO),indicates that the MgO particles can act as effective nucleation sites for α-Mg to reduce nucleation undercooling.According to the Hunt criteria,the critical temperature gradient for CET is greatly enhanced due to the significantly increased number density of MgO nucleation sites.In addition,the correlation with the thermal simulation results reveals a transition in the solidification conditions within the welding pool from the columnar grain zone to the equiaxed grain zone in the CET map,leading to the realization of CET.The exceptional grain refinement has contributed to a simultaneous improvement in the strength and plasticity of welded joints.This study presents a novel strategy for controlling equiaxed microstructure and optimizing mechanical properties in fusion welding or wire and arc additive manufacturing of Mg alloy components.
基金supported by the National Natural Science Foundation of China(No.52171041)the Science and Technology Special Project(K19168).
文摘During the tungsten inert gas(TIG)welding process of Ti_(2)AlNb alloy,high heat input leads to the formation of coarse grains,which are detrimental to the mechanical properties of welded joints.To address this problem,Ta microalloyed welding wires were developed to enhance the strength of the welded joints.The Ta-modifed fusion zone(FZ)exhibited a well-defned structure with a smooth,defect-free surface.Systematic analysis of the microstructure evolution and mechanical properties of the welded joints revealed that the Ta element completely dissolves into the FZ.During solidifcation,a signifcant constitutional undercooling efect occurs,promoting the columnar-to-equiaxed transition(CET)and reducing grain size from 187.42 to 133.49μm.Mechanical properties tests indicated that with increased Ta content,the strength of the welded joints initially increased and then decreased.When the Ta content in the welding wire was 1 wt%,the joints showed the best performance,with a tensile strength of 909.36 MPa and an elongation of 1.21%.Compared to the welded samples without Ta,the tensile strength and elongation increased by 153.01 MPa and 0.53%,respectively.Grain refnement and increased dislocation density were the main reasons for the improved mechanical properties.However,excessive Ta content led to signifcant the intragrain misorientation,increasing the joint’s anisotropy and causing uneven deformation during tensile testing.Therefore,further addition of Ta did not substantially enhance the tensile properties of the joint.Additionally,the paper provides a detailed analysis of the low elongation observed in the joint.After welding,dislocations were neatly arranged in the FZ,forming numerous parallel dislocation walls,leading to local stress concentration and accelerating crack initiation and propagation.Consequently,the elongation at the weld was lower than that of the base metal(BM).This research ofers a new approach to improve the mechanical properties of Ti2AlNb alloy during welding.
基金the National Natural Science Foundation of China(No.51871155).
文摘The effect of addition temperature of MgO particles(MgOp)on their dispersion behavior and the efficiency of grain refinement in AZ31 Mg alloy was investigated.In addition,the grain refinement mechanism was systematically studied by microstructure characterization,thermodynamic calculation,and analysis of solidification curves.The results show that the grain size of AZ31 Mg alloy initially decreases and then increases as the MgOp addition temperature is increased from 720 to 810℃,exhibiting a minimum value of 136μm at 780℃.The improved grain refinement efficiency with increasing MgOp addition temperature can be attributed to the reduced Mg melt viscosity and enhanced wettability between MgOp and Mg melt.Furthermore,a corresponding physical model describing the solidification behavior and grain refinement mechanism was proposed.
