Laser welding of dissimilar titanium/aluminum alloys has been employed at an increasing rate,particularly in the aerospace industry,owing to its advantages in terms of current design flexibility and fuel/cost savings....Laser welding of dissimilar titanium/aluminum alloys has been employed at an increasing rate,particularly in the aerospace industry,owing to its advantages in terms of current design flexibility and fuel/cost savings.The major problem with dissimilar Ti/Al welds arises from the difference in the thermal expansion and contraction of the two metals,which leads to hot-cracking susceptibility and the mitigation of the mechanical property after welding.In the present study,pulsed Nd:YAG laser welding of Ti6 Al4 V and AA6060 has been addressed.Hot-cracking susceptibility in the heat affected zone and the shear fracture behavior of the lap joints were investigated through microstructural characterization and mechanical tests.The results indicate that the hot cracking tendency can be reduced by increasing the pulse peak power(7.5–8.5 kW)and the laser point diameter(0.8–1.0 mm)with specific pulse duration and overlap.An alternative control strategy for less hot cracks in the Ti/Al lap joint can be to increase the weld width and decrease the cooling rate during solidification.The shear fracture of the Ti/Al lap joint is likely to occur along the lower side path of the weld interface with decreasing weld surface collapsed amount and increasing aluminum base metal melt depth.展开更多
This paper examined the impact of the number of thermal cycles and augmented strain on hot cracking in AZ31 and AZ61 magnesium alloy. Statistical analyses were performed. Following observation using a scanning electro...This paper examined the impact of the number of thermal cycles and augmented strain on hot cracking in AZ31 and AZ61 magnesium alloy. Statistical analyses were performed. Following observation using a scanning electron microscope （SEM）, an energy dispersive spectrometer （EDS） was used for component analysis. Results showed that Al content in magnesium alloy has an effect on hot cracking susceptibility. In addition, the nonequilibrium solidification process produced segregation in Al content, causing higher liquid Mg-alloy rich Al content at grain boundaries, and resulting into liquefied grain boundaries of partially melted zone （PMZ）. In summary, under multiple thermal cycles AZ61 produced serious liquation cracking. AZ61 has higher （6 wt%） Al content and produced much liquefied Mg17Al12 at grain boundaries under multiple thermal cycles. The liquefied Mg17Al12 were pulled apart and hot cracks formed at weld metal HAZ due to the augmented strain. Since AZ31 had half the Al content of AZ61, its hot-cracking susceptibility was lower than AZ61. In addition, AZ61 showed longer total crack length （TCL） in one thermal cycle compared to that in three thermal cycles. This phenomenon was possibly due to high-temperature gasification of Al during the welding process, which resulted in lower overall Al content. Consequently, shorter hot cracks exhibited in three thermal cycles. It was found the Al content of AZ31 and AZ61 can be used to assess the hot-cracking susceptibility.展开更多
基金The supports from the National Natural Science Foundation of China(No.51705080,No.51805087)the Natural Science Foundation of Fujian Province(No.2018J01761,No.2018J01764)。
文摘Laser welding of dissimilar titanium/aluminum alloys has been employed at an increasing rate,particularly in the aerospace industry,owing to its advantages in terms of current design flexibility and fuel/cost savings.The major problem with dissimilar Ti/Al welds arises from the difference in the thermal expansion and contraction of the two metals,which leads to hot-cracking susceptibility and the mitigation of the mechanical property after welding.In the present study,pulsed Nd:YAG laser welding of Ti6 Al4 V and AA6060 has been addressed.Hot-cracking susceptibility in the heat affected zone and the shear fracture behavior of the lap joints were investigated through microstructural characterization and mechanical tests.The results indicate that the hot cracking tendency can be reduced by increasing the pulse peak power(7.5–8.5 kW)and the laser point diameter(0.8–1.0 mm)with specific pulse duration and overlap.An alternative control strategy for less hot cracks in the Ti/Al lap joint can be to increase the weld width and decrease the cooling rate during solidification.The shear fracture of the Ti/Al lap joint is likely to occur along the lower side path of the weld interface with decreasing weld surface collapsed amount and increasing aluminum base metal melt depth.
文摘This paper examined the impact of the number of thermal cycles and augmented strain on hot cracking in AZ31 and AZ61 magnesium alloy. Statistical analyses were performed. Following observation using a scanning electron microscope （SEM）, an energy dispersive spectrometer （EDS） was used for component analysis. Results showed that Al content in magnesium alloy has an effect on hot cracking susceptibility. In addition, the nonequilibrium solidification process produced segregation in Al content, causing higher liquid Mg-alloy rich Al content at grain boundaries, and resulting into liquefied grain boundaries of partially melted zone （PMZ）. In summary, under multiple thermal cycles AZ61 produced serious liquation cracking. AZ61 has higher （6 wt%） Al content and produced much liquefied Mg17Al12 at grain boundaries under multiple thermal cycles. The liquefied Mg17Al12 were pulled apart and hot cracks formed at weld metal HAZ due to the augmented strain. Since AZ31 had half the Al content of AZ61, its hot-cracking susceptibility was lower than AZ61. In addition, AZ61 showed longer total crack length （TCL） in one thermal cycle compared to that in three thermal cycles. This phenomenon was possibly due to high-temperature gasification of Al during the welding process, which resulted in lower overall Al content. Consequently, shorter hot cracks exhibited in three thermal cycles. It was found the Al content of AZ31 and AZ61 can be used to assess the hot-cracking susceptibility.
