The aim of this work is to investigate the mechanical properties and microstructures of friction-stir welded(FSWed) St52 structural steel joints. In this study, St52 steel plates with a thickness of 4 mm were butt-wel...The aim of this work is to investigate the mechanical properties and microstructures of friction-stir welded(FSWed) St52 structural steel joints. In this study, St52 steel plates with a thickness of 4 mm were butt-welded by friction-stir welding(FSW) using a tungsten carbide tool having a conical pin. The microstructure of the welded zone consists of equiaxed fine ferrite, grain boundary ferrite, Widmanstatten ferrite, and aggregates of ferrite + cementite. The microhardness measurements showed that the hardness of the welded zone was significantly higher than that of the base metal. The FSWed St52 joint exhibited a significant strength overmatching in the weld region and a strength performance similar to or slightly higher than that of the base plate.展开更多
In this work, the current understanding and development of fliction-stir welding and processing of Ti- 6Al-4V alloy are briefly reviewed. The critical issues of these processes are addressed, including welding tool ma...In this work, the current understanding and development of fliction-stir welding and processing of Ti- 6Al-4V alloy are briefly reviewed. The critical issues of these processes are addressed, including welding tool materials and design, tool wea,, processing temperature, material flow, processing window and residual stresses. A particular emphasis is given to microstructural aspects and microstructure-properties relationship. Potential engineering applications are highlighted.展开更多
The present work was undertaken to improve superplastic ductility of friction-stir welded joints of ultrafine-grained(UFG)Al-Mg-Sc-Zr alloy.In order to suppress the undesirable abnormal grain growth,which typically oc...The present work was undertaken to improve superplastic ductility of friction-stir welded joints of ultrafine-grained(UFG)Al-Mg-Sc-Zr alloy.In order to suppress the undesirable abnormal grain growth,which typically occurs in the heavily deformed base material,the UFG material was produced at elevated temperature.It was suggested that the new processing route could reduce dislocation density in the UFG structure and thus enhance its thermal stability.It was found,however,that the new approach resulted in a relatively high fraction of low-angle boundaries which,in turn,retarded grain-boundary sliding during subsequent superplastic tests.Therefore,despite the successful inhibition of the abnormal grain growth in the base-material zone,the superplastic deformation was still preferentially concentrated in the fully-recrystallized stir zone of the material.As a result,the maximal elongation-to-failure did not exceed 700%.展开更多
The process of friction-stir welding 2A12CZ alloy has been studied. And strength and elongation tests have been performed, which demonstrated that the opportunity existed to manipulate friction-stir welding parameters...The process of friction-stir welding 2A12CZ alloy has been studied. And strength and elongation tests have been performed, which demonstrated that the opportunity existed to manipulate friction-stir welding parameters in order to improve a range of material properties. The results showed that the joint strength and elongation arrived at their maximums (331 MPa and 4%) at 37.5 mm/min and 300 rpm. As welding parameters changing, joint tensile strength and elongation had similar development. Hardness measurement indicated that the weld was softened. However, there was considerable difference in softening degree for different joint zone. The weld top had lower hardness and wider softening zone than other zone of the weld. And softening zone at advancing side was wider than that at retreating side.展开更多
Friction stir lap welding of a DP1180 advanced ultrahigh strength steel was successfully carried out by using three welding tools with different pin lengths. The effects of the welding heat input and material flow on ...Friction stir lap welding of a DP1180 advanced ultrahigh strength steel was successfully carried out by using three welding tools with different pin lengths. The effects of the welding heat input and material flow on the microstructure evolution of the joints were analyzed in detail. The relationship between pin length and mechanical properties of lap joints was studied. The results showed that the peak temperatures of all joints exceeded A c3, and martensite phases with similar morphologies were formed in the stir zones. These martensite retained good toughness due to the self-tempering effect. The formation of ferrite and tempered martensite was the main reason for the hardness reduction in heat-affected zone. The mechanical properties of the lap joints were determined by loading mode, features of lap interface and the joint defects. When the stir pin was inserted into the lower sheet with a depth of 0.4 mm, the lap joint exhibited the maximum tensile strength of 12.4 kN.展开更多
In this study, the effects of tool rotational speed, tool traverse speed, and Zn content on the grain size and hardness of the friction-stir-welded （FSWed） Cu-Zn alloy joints were investigated. The microstructures o...In this study, the effects of tool rotational speed, tool traverse speed, and Zn content on the grain size and hardness of the friction-stir-welded （FSWed） Cu-Zn alloy joints were investigated. The microstructures of the joints were examined using optical microscope （OM） and scanning transmission electron microscope （STEM）. Vickers hardness test was conducted to evaluate the hardness of the joints. In addition, the relationships between the process parameters, grain size, and hardness of the joints were established. The results show that the developed relationships predict the grain size and hardness of the joints accurately. The Zn content of the alloys is the most effective parameter on the grain size and hardness, where the tool traverse speed has the minimum effect. The relationship between the hardness and grain size of the joints has a deviation from the Hall-Petch equation due to formation of high dislocation density inside the grains. At higher Zn amounts, the dislocation tangles with high density form instead of dislocation cells, and hence, lower conformity with the Hall-Petch relationship is observed.展开更多
Commercial A7020-T6 plates in the overaged state were subjected to friction stir welding with four different tool rotational speeds of 500, 710, 1000, and 1400 r/min and a single traverse feed rate of 40 mm/min. The r...Commercial A7020-T6 plates in the overaged state were subjected to friction stir welding with four different tool rotational speeds of 500, 710, 1000, and 1400 r/min and a single traverse feed rate of 40 mm/min. The resultant changes in the welding heat input, microstructure, and the mechanical properties of the joints were investigated. The changes were related to the processes of growth, dissolution, and re-formation of precipitates. The precipitate evolution was examined by differential scanning calorimetry, and the microstructural analysis was conducted using optical, scanning, and transmission electron microscopes. The results showed that the grain size in the stirred zone(SZ) decreased substantially compared with the base metal, but increased with tool rotational speed because of the rise in temperature. We found that the width of the heat-affected zone increased with tool rotational speed. The hardness and the tensile strength in the SZ increased with increasing heat input compared with the base metal in the overaged condition. This recovery in mechanical properties of the joints can be attributed to the dissolution and re-formation of precipitates in the SZ and the thermomechanically affected zone. This process is referred to as an "auto-aging treatment."展开更多
The corrosion behavior of friction-stir-welded 2A14-T6 aluminum alloy was investigated by immersion testing in immersion exfoliation corrosion（EXCO） solution. Electrochemical measurements（open circuit potential, po...The corrosion behavior of friction-stir-welded 2A14-T6 aluminum alloy was investigated by immersion testing in immersion exfoliation corrosion（EXCO） solution. Electrochemical measurements（open circuit potential, potentiodynamic polarization curves, and electrochemical impedance spectroscopy）, scanning electron microscopy, and energy dispersive spectroscopy were employed for analyzing the corrosion mechanism. The results show that, compared to the base material, the corrosion resistance of the friction-stir welds is greatly improved, and the weld nugget has the highest corrosion resistance. The pitting susceptibility originates from the edge of Al-Cu-Fe-Mn-Si phase particles as the cathode compared to the matrix due to their high self-corrosion potential. No corrosion activity is observed around the θ phase（Al2Cu） after 2 h of immersion in EXCO solution.展开更多
Friction stir welding(FSW) technique was utilized to weld cast AM50 magnesium alloy plates.The microstructures in the base metal(BM) and the weld joint were observed by optical microscopy.The mechanical properties wer...Friction stir welding(FSW) technique was utilized to weld cast AM50 magnesium alloy plates.The microstructures in the base metal(BM) and the weld joint were observed by optical microscopy.The mechanical properties were investigated by using hardness measurement and tensile test,and the fractographs were observed by scanning electron microscopy.The results show that the microstructure of the base material was characterized by bulk primaryαphase,α-matrix and intermetallic compoundβ(or Mg_(17)Al_(12)),and the weld nugget exhibiting recrystallized microstructure consists ofα-matrix andβphase.The grain size in the weld is smaller than that in the base metal.The hardness of the weld joint is improved but the tensile strength and yield strength,as well as the elongation to failure of the base material decline.The fracture of BM has a rougher surface with more dimples,which is a characteristic of the ductile fracture,whereas the fracture on the nugget reveals a quasi-cleavage feature.The ultimate tensile strength and yield strength of the FSWed AM50 are 86.2%and 94.0%of those of the base metal,respectively.展开更多
搅拌摩擦焊接过程中,摩擦扭矩和焊接温度场反映了母材的塑性变形状态。本工作对7075-T6铝合金无缝管环形焊缝进行封焊,采用主轴电机电压电流(Voltage and current of main shaft motor,VCMSM)法计算出不同摩擦转速、焊接速度和焊接顺序...搅拌摩擦焊接过程中,摩擦扭矩和焊接温度场反映了母材的塑性变形状态。本工作对7075-T6铝合金无缝管环形焊缝进行封焊,采用主轴电机电压电流(Voltage and current of main shaft motor,VCMSM)法计算出不同摩擦转速、焊接速度和焊接顺序下搅拌摩擦焊过程中搅拌头与母材间的摩擦扭矩,并对焊缝温度进行采集。结果表明,摩擦扭矩在经历两次波动后逐渐趋于稳定并建立稳定摩擦的趋势,摩擦扭矩波动较小的工艺参数焊缝成形较好;焊接过程温度峰值主要受到工艺参数的影响,前进侧在管件内侧焊接温度峰值比前进侧在外侧更高。展开更多
采用冷金属过渡焊接(Cold metal transfer welding, CMT)对4 mm厚的410不锈钢进行焊接,焊后对CMT接头进行搅拌摩擦加工(Friction stir processing, FSP)。采用光学显微镜、扫描电镜、万能试验机和显微硬度仪等研究了CMT接头和FSP后接头...采用冷金属过渡焊接(Cold metal transfer welding, CMT)对4 mm厚的410不锈钢进行焊接,焊后对CMT接头进行搅拌摩擦加工(Friction stir processing, FSP)。采用光学显微镜、扫描电镜、万能试验机和显微硬度仪等研究了CMT接头和FSP后接头的表面形貌、微观结构和力学性能。结果表明:410不锈钢CMT接头经过FSP处理后,接头焊缝表面成型良好,内部无孔洞等缺陷,焊缝由大尺寸的柱状晶转变为细小的等轴晶,平均晶粒尺寸由155.07μm减小到17.78μm,大角度晶界比例从41.3%显著增加到67.19%;FSP接头焊核区的平均硬度达到300 HV0.2,抗拉强度为575.48 MPa,相比CMT焊接接头(514.27 MPa)提升了12%,伸长率从10%降至6%。展开更多
文摘The aim of this work is to investigate the mechanical properties and microstructures of friction-stir welded(FSWed) St52 structural steel joints. In this study, St52 steel plates with a thickness of 4 mm were butt-welded by friction-stir welding(FSW) using a tungsten carbide tool having a conical pin. The microstructure of the welded zone consists of equiaxed fine ferrite, grain boundary ferrite, Widmanstatten ferrite, and aggregates of ferrite + cementite. The microhardness measurements showed that the hardness of the welded zone was significantly higher than that of the base metal. The FSWed St52 joint exhibited a significant strength overmatching in the weld region and a strength performance similar to or slightly higher than that of the base plate.
文摘In this work, the current understanding and development of fliction-stir welding and processing of Ti- 6Al-4V alloy are briefly reviewed. The critical issues of these processes are addressed, including welding tool materials and design, tool wea,, processing temperature, material flow, processing window and residual stresses. A particular emphasis is given to microstructural aspects and microstructure-properties relationship. Potential engineering applications are highlighted.
基金financially supported by the Russian Science Foundation(No.18-79-10174)。
文摘The present work was undertaken to improve superplastic ductility of friction-stir welded joints of ultrafine-grained(UFG)Al-Mg-Sc-Zr alloy.In order to suppress the undesirable abnormal grain growth,which typically occurs in the heavily deformed base material,the UFG material was produced at elevated temperature.It was suggested that the new processing route could reduce dislocation density in the UFG structure and thus enhance its thermal stability.It was found,however,that the new approach resulted in a relatively high fraction of low-angle boundaries which,in turn,retarded grain-boundary sliding during subsequent superplastic tests.Therefore,despite the successful inhibition of the abnormal grain growth in the base-material zone,the superplastic deformation was still preferentially concentrated in the fully-recrystallized stir zone of the material.As a result,the maximal elongation-to-failure did not exceed 700%.
文摘The process of friction-stir welding 2A12CZ alloy has been studied. And strength and elongation tests have been performed, which demonstrated that the opportunity existed to manipulate friction-stir welding parameters in order to improve a range of material properties. The results showed that the joint strength and elongation arrived at their maximums (331 MPa and 4%) at 37.5 mm/min and 300 rpm. As welding parameters changing, joint tensile strength and elongation had similar development. Hardness measurement indicated that the weld was softened. However, there was considerable difference in softening degree for different joint zone. The weld top had lower hardness and wider softening zone than other zone of the weld. And softening zone at advancing side was wider than that at retreating side.
基金supported by the National Natural Science Foundation of China (Nos. 51671190, 51774085 and 51471171).
文摘Friction stir lap welding of a DP1180 advanced ultrahigh strength steel was successfully carried out by using three welding tools with different pin lengths. The effects of the welding heat input and material flow on the microstructure evolution of the joints were analyzed in detail. The relationship between pin length and mechanical properties of lap joints was studied. The results showed that the peak temperatures of all joints exceeded A c3, and martensite phases with similar morphologies were formed in the stir zones. These martensite retained good toughness due to the self-tempering effect. The formation of ferrite and tempered martensite was the main reason for the hardness reduction in heat-affected zone. The mechanical properties of the lap joints were determined by loading mode, features of lap interface and the joint defects. When the stir pin was inserted into the lower sheet with a depth of 0.4 mm, the lap joint exhibited the maximum tensile strength of 12.4 kN.
文摘In this study, the effects of tool rotational speed, tool traverse speed, and Zn content on the grain size and hardness of the friction-stir-welded （FSWed） Cu-Zn alloy joints were investigated. The microstructures of the joints were examined using optical microscope （OM） and scanning transmission electron microscope （STEM）. Vickers hardness test was conducted to evaluate the hardness of the joints. In addition, the relationships between the process parameters, grain size, and hardness of the joints were established. The results show that the developed relationships predict the grain size and hardness of the joints accurately. The Zn content of the alloys is the most effective parameter on the grain size and hardness, where the tool traverse speed has the minimum effect. The relationship between the hardness and grain size of the joints has a deviation from the Hall-Petch equation due to formation of high dislocation density inside the grains. At higher Zn amounts, the dislocation tangles with high density form instead of dislocation cells, and hence, lower conformity with the Hall-Petch relationship is observed.
基金financial support provided by Shahid Chamran University of Ahvaz, Iran
文摘Commercial A7020-T6 plates in the overaged state were subjected to friction stir welding with four different tool rotational speeds of 500, 710, 1000, and 1400 r/min and a single traverse feed rate of 40 mm/min. The resultant changes in the welding heat input, microstructure, and the mechanical properties of the joints were investigated. The changes were related to the processes of growth, dissolution, and re-formation of precipitates. The precipitate evolution was examined by differential scanning calorimetry, and the microstructural analysis was conducted using optical, scanning, and transmission electron microscopes. The results showed that the grain size in the stirred zone(SZ) decreased substantially compared with the base metal, but increased with tool rotational speed because of the rise in temperature. We found that the width of the heat-affected zone increased with tool rotational speed. The hardness and the tensile strength in the SZ increased with increasing heat input compared with the base metal in the overaged condition. This recovery in mechanical properties of the joints can be attributed to the dissolution and re-formation of precipitates in the SZ and the thermomechanically affected zone. This process is referred to as an "auto-aging treatment."
基金financially supported by the National Natural Science Foundation of China (No. 51105030)
文摘The corrosion behavior of friction-stir-welded 2A14-T6 aluminum alloy was investigated by immersion testing in immersion exfoliation corrosion（EXCO） solution. Electrochemical measurements（open circuit potential, potentiodynamic polarization curves, and electrochemical impedance spectroscopy）, scanning electron microscopy, and energy dispersive spectroscopy were employed for analyzing the corrosion mechanism. The results show that, compared to the base material, the corrosion resistance of the friction-stir welds is greatly improved, and the weld nugget has the highest corrosion resistance. The pitting susceptibility originates from the edge of Al-Cu-Fe-Mn-Si phase particles as the cathode compared to the matrix due to their high self-corrosion potential. No corrosion activity is observed around the θ phase（Al2Cu） after 2 h of immersion in EXCO solution.
基金Project(2007AC4073)supported by Chongqing Munciple Scicnce-Tech Tackle Program,ChinaProject(2008BB0063)supported by theNatural Science Foundation of Chongqing Science and Technology Commission,China
文摘Friction stir welding(FSW) technique was utilized to weld cast AM50 magnesium alloy plates.The microstructures in the base metal(BM) and the weld joint were observed by optical microscopy.The mechanical properties were investigated by using hardness measurement and tensile test,and the fractographs were observed by scanning electron microscopy.The results show that the microstructure of the base material was characterized by bulk primaryαphase,α-matrix and intermetallic compoundβ(or Mg_(17)Al_(12)),and the weld nugget exhibiting recrystallized microstructure consists ofα-matrix andβphase.The grain size in the weld is smaller than that in the base metal.The hardness of the weld joint is improved but the tensile strength and yield strength,as well as the elongation to failure of the base material decline.The fracture of BM has a rougher surface with more dimples,which is a characteristic of the ductile fracture,whereas the fracture on the nugget reveals a quasi-cleavage feature.The ultimate tensile strength and yield strength of the FSWed AM50 are 86.2%and 94.0%of those of the base metal,respectively.
文摘搅拌摩擦焊接过程中,摩擦扭矩和焊接温度场反映了母材的塑性变形状态。本工作对7075-T6铝合金无缝管环形焊缝进行封焊,采用主轴电机电压电流(Voltage and current of main shaft motor,VCMSM)法计算出不同摩擦转速、焊接速度和焊接顺序下搅拌摩擦焊过程中搅拌头与母材间的摩擦扭矩,并对焊缝温度进行采集。结果表明,摩擦扭矩在经历两次波动后逐渐趋于稳定并建立稳定摩擦的趋势,摩擦扭矩波动较小的工艺参数焊缝成形较好;焊接过程温度峰值主要受到工艺参数的影响,前进侧在管件内侧焊接温度峰值比前进侧在外侧更高。
