Friction stir welding （FSW） of 6061 aluminium alloy butt joint was carried out at each rotation speed of 600, 800, 1000, 1200 r/min for two different travel speeds, 80 and 100 mm/min, at a constant probe depth of 1....Friction stir welding （FSW） of 6061 aluminium alloy butt joint was carried out at each rotation speed of 600, 800, 1000, 1200 r/min for two different travel speeds, 80 and 100 mm/min, at a constant probe depth of 1.85 mm. The calculated energy input based on the FSW parameters studied shows that the ultimate tensile strength （UTS） of the butt joint is obtained within a certain range of energy input of 297 kJ to 354 kJ out of total range of energy input studied from 196 kJ to 405 kJ. The fatigue behaviors of high-strength and low-strength joints performed at different stress ratios, i.e., 0.5, 0.3, 0.1, -0.3, -0.5, indicate that the fatigue behaviors of both the welds are sensitive to the microstructural features, such as stir zone （SZ）, thermo mechanically affected zone （TMAZ） and heat affected zone （HAZ）. The observed fatigue strengths were discussed in terms of the microstructure, crack path behavior and fracture surface.展开更多
A new friction-based riveting technique, Rotating Hammer Riveting(RHR), is demonstrated to fully form AZ31 Mg rivet heads in a mere 0.23 s. Heat and pressure generated through severe plastic deformation during the pro...A new friction-based riveting technique, Rotating Hammer Riveting(RHR), is demonstrated to fully form AZ31 Mg rivet heads in a mere 0.23 s. Heat and pressure generated through severe plastic deformation during the process was sufficient to form the Mg rivet head without the need for a pre-heating operation. Due to preliminary twinning and followed by dynamic recrystallization, AZ31 Mg grains in the rivet head were refined during RHR, which enhance the formability of Mg rivets by triggering grain boundary sliding and reducing plastic anisotropy of Mg. In addition, RHR joints showed a metallurgical bond between the rivet head and top AZ31 Mg sheet, which eliminates a significant pathway for corrosion.展开更多
We demonstrate generalizable semantic segmentation using minimal ground truth data.Correlated scanning electron microscopy(SEM)images and electron backscatter diffraction(EBSD)measurements of friction-stir processed 3...We demonstrate generalizable semantic segmentation using minimal ground truth data.Correlated scanning electron microscopy(SEM)images and electron backscatter diffraction(EBSD)measurements of friction-stir processed 316L stainless steel plates were used to train deep learning models for grain boundary segmentation.Secondary electron(SE)imaging taken at 10 keV correlated to EBSD-derived grain boundaries produced the best performing model.Notably,an ensemble of three models trained on a single SE image produced accurate segmentation over a series of backscatter electron(BSE)images of samples manufactured under different processing parameters,with a mean absolute error in grain size of 0.34μm.The generalizability of the models likely results from the similar escape depths of the SE training input and the EBSD training output and the reduced probability of stored strain artifacts appearing in the image.This highlights the importance of considering the physical principles behind imaging to develop robust models for microstructure characterization.展开更多
Joining magnesium(Mg)alloys to steel is difficult due to metallurgical incompatibility.Applying a zinc(Zn)coating to steel enables formation of a thin Mg-Zn eutectic phase layer during welding,which promotes strong bo...Joining magnesium(Mg)alloys to steel is difficult due to metallurgical incompatibility.Applying a zinc(Zn)coating to steel enables formation of a thin Mg-Zn eutectic phase layer during welding,which promotes strong bonding.However,in joints created with Friction-stir assisted scribe technology(FAST),this Mg-Zn eutectic phase layer occasionally extends from the interface to the surface of the Mg sheet.This phenomenon is attributed to the formation of a liquid-state Mg-Zn eutectic phase,coupled with the distinctive material flow induced by the FAST tool.Microstructural analysis confirmed that the Mg-Zn eutectic phase comprisesα-Mg and the Mg_(21)Zn_(25)intermetallic compound.Lap shear tensile tests revealed that when the Mg-Zn eutectic phase migration pathway aligned with the stir zone boundary,it led to reduced joint strength and premature fracture along the eutectic phase pathway.This indicates that liquid metal embrittlement(LME)occurred during FAST joining of Mg alloy and galvanized steel.These findings highlight the critical importance of controlling tool features and process parameters in FAST welding to prevent LME-related failures in dissimilar Mg/steel assemblies.展开更多
文摘Friction stir welding （FSW） of 6061 aluminium alloy butt joint was carried out at each rotation speed of 600, 800, 1000, 1200 r/min for two different travel speeds, 80 and 100 mm/min, at a constant probe depth of 1.85 mm. The calculated energy input based on the FSW parameters studied shows that the ultimate tensile strength （UTS） of the butt joint is obtained within a certain range of energy input of 297 kJ to 354 kJ out of total range of energy input studied from 196 kJ to 405 kJ. The fatigue behaviors of high-strength and low-strength joints performed at different stress ratios, i.e., 0.5, 0.3, 0.1, -0.3, -0.5, indicate that the fatigue behaviors of both the welds are sensitive to the microstructural features, such as stir zone （SZ）, thermo mechanically affected zone （TMAZ） and heat affected zone （HAZ）. The observed fatigue strengths were discussed in terms of the microstructure, crack path behavior and fracture surface.
基金the support of the U.S.Department of Energy Vehicle Technologies Office(DOE/VTO)Joining Core Program。
文摘A new friction-based riveting technique, Rotating Hammer Riveting(RHR), is demonstrated to fully form AZ31 Mg rivet heads in a mere 0.23 s. Heat and pressure generated through severe plastic deformation during the process was sufficient to form the Mg rivet head without the need for a pre-heating operation. Due to preliminary twinning and followed by dynamic recrystallization, AZ31 Mg grains in the rivet head were refined during RHR, which enhance the formability of Mg rivets by triggering grain boundary sliding and reducing plastic anisotropy of Mg. In addition, RHR joints showed a metallurgical bond between the rivet head and top AZ31 Mg sheet, which eliminates a significant pathway for corrosion.
文摘We demonstrate generalizable semantic segmentation using minimal ground truth data.Correlated scanning electron microscopy(SEM)images and electron backscatter diffraction(EBSD)measurements of friction-stir processed 316L stainless steel plates were used to train deep learning models for grain boundary segmentation.Secondary electron(SE)imaging taken at 10 keV correlated to EBSD-derived grain boundaries produced the best performing model.Notably,an ensemble of three models trained on a single SE image produced accurate segmentation over a series of backscatter electron(BSE)images of samples manufactured under different processing parameters,with a mean absolute error in grain size of 0.34μm.The generalizability of the models likely results from the similar escape depths of the SE training input and the EBSD training output and the reduced probability of stored strain artifacts appearing in the image.This highlights the importance of considering the physical principles behind imaging to develop robust models for microstructure characterization.
基金PNNL is operated by Battelle Memorial Institute for the U.S.Department of Energy under contract DE-AC05-76RL01830sponsored by the DOEEERE,Vehicle Technology Office,through the Joining Core Program.
文摘Joining magnesium(Mg)alloys to steel is difficult due to metallurgical incompatibility.Applying a zinc(Zn)coating to steel enables formation of a thin Mg-Zn eutectic phase layer during welding,which promotes strong bonding.However,in joints created with Friction-stir assisted scribe technology(FAST),this Mg-Zn eutectic phase layer occasionally extends from the interface to the surface of the Mg sheet.This phenomenon is attributed to the formation of a liquid-state Mg-Zn eutectic phase,coupled with the distinctive material flow induced by the FAST tool.Microstructural analysis confirmed that the Mg-Zn eutectic phase comprisesα-Mg and the Mg_(21)Zn_(25)intermetallic compound.Lap shear tensile tests revealed that when the Mg-Zn eutectic phase migration pathway aligned with the stir zone boundary,it led to reduced joint strength and premature fracture along the eutectic phase pathway.This indicates that liquid metal embrittlement(LME)occurred during FAST joining of Mg alloy and galvanized steel.These findings highlight the critical importance of controlling tool features and process parameters in FAST welding to prevent LME-related failures in dissimilar Mg/steel assemblies.
