Welding joint of GH4169 alloy with a good formation was obtained. No macroscopic defects occurred in the joint. The weld had mainly a dendritic structure; the base metal was a solid solution of Ni, Cr, and Fe, and the...Welding joint of GH4169 alloy with a good formation was obtained. No macroscopic defects occurred in the joint. The weld had mainly a dendritic structure; the base metal was a solid solution of Ni, Cr, and Fe, and the strengthening-phase particles such as Ni3Nb were dispersively distributed along the grain boundary. The average tensile strength of the joint reached 743.7 MPa, and the Vickers hardness of the weld exceeded HV 300. Because of the segregation of the low-melting compound Ni3Nb at the grain boundary of the fusion zone, liquid cracks tended to occur as a result of welding stress. The formation of liquid cracks was inhibited by adding an alloying element, Mn, to the welding bath, because Mn diffused to the fusion zone and the high-melting phase Mn2Nb formed, and thus the overall properties of the joint were improved.展开更多
Fatigue characteristics of A7N01 aluminium alloy welded joint were investigated and a fatigue crack initiation life-based model was proposed. The difference of fatigue crack initiation life among base metal, weld meta...Fatigue characteristics of A7N01 aluminium alloy welded joint were investigated and a fatigue crack initiation life-based model was proposed. The difference of fatigue crack initiation life among base metal, weld metal and heat affected zone (HAZ) is slight. Furthermore, the ratio of fatigue crack initiation life (Ni) to fatigue life to failure(Nf) is a material dependent parameter, 26.32%, 40.21% and 60.67% for base metal, HAZ and weld metal, respectively. Total fatigue life predicted using the presented model is in good agreement with the experimental data and that using Basquin’s model. The observation results of fatigue fracture surfaces, using scanning electron microscope (SEM), demonstrate that fatigue crack initiates from smooth surface due to welding process for weld metal, blowhole in HAZ causes fatigue crack initiation, and the crushed second phase particles play an important part in fatigue crack initiation in base metal.展开更多
In this investigation, 2024 aluminium alloy plates were friction stir welded, a sequence of experiments was performedincluding fatigue and crack propagation tests in air, under pre-corrosion and in a 3.5% NaCl solutio...In this investigation, 2024 aluminium alloy plates were friction stir welded, a sequence of experiments was performedincluding fatigue and crack propagation tests in air, under pre-corrosion and in a 3.5% NaCl solution, in combination withfractography analyses of near-threshold region, Paris region and finial fracture region with the aid of scanning electron microscopy（SEM）. Results showed that the corrosive environment caused a dramatical decrease in fatigue lives of FS welds, the corrosionfatigue lives of FS welds were almost a half of those of the as-welded specimens. The crack growth rates in FS welds were higherthan their counterparts in base materials, under the corrosive environment, the crack growth rate differences between base materialsand FS welds become increasingly apparent with the increase of stress intensity factor range ΔK, but the pre-corrosion process hadlittle effect on the FS welds’ crack propagation behavior except for shortening the crack initiation lives greatly.展开更多
In order to clarify the characteristics and formation mechanism of the reheat cracking in Ti2AlNb weldments,a series of heat treatment conditions were performed to the circular joints welded by electron beam,and then ...In order to clarify the characteristics and formation mechanism of the reheat cracking in Ti2AlNb weldments,a series of heat treatment conditions were performed to the circular joints welded by electron beam,and then the macrostructures and microstructures were investigated using optical microscopy,scanning electron microscopy,X-ray diffractometry,and transmission electron microscopy.The results show that the reheat cracking occurs primarily along the grain boundaries in the weld when the Ti2AlNb circular welded joints are heated up to about 700℃.During the heat treatment,an almost complete transformation of B2→O happens while the temperature goes up through the O single-phase region.Then,O→B2+O phase transformation occurs primarily along the grain boundaries as the weld metal continues to heat up to the B2+O dual-phase region.Under the high tension stress consisting of welding residual stress and phase transformation stress,reheat cracking occurs at the interface between the B2+O dual-phase layer and the O-phase matrix.展开更多
The aim of the present work is to evaluate the fatigue crack growth behaviour of 12 mm thick AA 7075-T651 aluminium alloy plates joined by FSW. Fatigue crack growth test was carried out on center cracked tensile (CCT)...The aim of the present work is to evaluate the fatigue crack growth behaviour of 12 mm thick AA 7075-T651 aluminium alloy plates joined by FSW. Fatigue crack growth test was carried out on center cracked tensile (CCT) specimens extracted from the FSW joints and unwelded parent metal. Transverse tensile properties of the unwelded parent metal and welded joints were evaluated. Microstructures of the welded joints were analyzed using optical microscopy and transmission electron microscopy. The scanning electron microscope was used to characterize the fracture surfaces. It was found that the ΔKcr of the welded joint is reduced by 10×10-3 MPa·m1/2 in comparison with the unwelded parent metal. Hence, the fatigue life of the friction stir welded AA 7075-T651aluminium alloy joints is appreciably lower than that of the unwelded parent metal, which is attributed to the dissolution of precipitates in the weld region during friction stir welding.展开更多
基金Project(HIT.NSRIF.2014007)supported by the Fundamental Research Funds for the Central Universities,China
文摘Welding joint of GH4169 alloy with a good formation was obtained. No macroscopic defects occurred in the joint. The weld had mainly a dendritic structure; the base metal was a solid solution of Ni, Cr, and Fe, and the strengthening-phase particles such as Ni3Nb were dispersively distributed along the grain boundary. The average tensile strength of the joint reached 743.7 MPa, and the Vickers hardness of the weld exceeded HV 300. Because of the segregation of the low-melting compound Ni3Nb at the grain boundary of the fusion zone, liquid cracks tended to occur as a result of welding stress. The formation of liquid cracks was inhibited by adding an alloying element, Mn, to the welding bath, because Mn diffused to the fusion zone and the high-melting phase Mn2Nb formed, and thus the overall properties of the joint were improved.
文摘Fatigue characteristics of A7N01 aluminium alloy welded joint were investigated and a fatigue crack initiation life-based model was proposed. The difference of fatigue crack initiation life among base metal, weld metal and heat affected zone (HAZ) is slight. Furthermore, the ratio of fatigue crack initiation life (Ni) to fatigue life to failure(Nf) is a material dependent parameter, 26.32%, 40.21% and 60.67% for base metal, HAZ and weld metal, respectively. Total fatigue life predicted using the presented model is in good agreement with the experimental data and that using Basquin’s model. The observation results of fatigue fracture surfaces, using scanning electron microscope (SEM), demonstrate that fatigue crack initiates from smooth surface due to welding process for weld metal, blowhole in HAZ causes fatigue crack initiation, and the crushed second phase particles play an important part in fatigue crack initiation in base metal.
基金Project(51405309)supported by the National Natural Science Foundation of ChinaProject(L2014065)supported by the General Project of Scientific Research of Liaoning Provincial Education Department,ChinaProject(2013024011)supported by the Natural Science Foundation of Liaoning Province,China
文摘In this investigation, 2024 aluminium alloy plates were friction stir welded, a sequence of experiments was performedincluding fatigue and crack propagation tests in air, under pre-corrosion and in a 3.5% NaCl solution, in combination withfractography analyses of near-threshold region, Paris region and finial fracture region with the aid of scanning electron microscopy（SEM）. Results showed that the corrosive environment caused a dramatical decrease in fatigue lives of FS welds, the corrosionfatigue lives of FS welds were almost a half of those of the as-welded specimens. The crack growth rates in FS welds were higherthan their counterparts in base materials, under the corrosive environment, the crack growth rate differences between base materialsand FS welds become increasingly apparent with the increase of stress intensity factor range ΔK, but the pre-corrosion process hadlittle effect on the FS welds’ crack propagation behavior except for shortening the crack initiation lives greatly.
文摘In order to clarify the characteristics and formation mechanism of the reheat cracking in Ti2AlNb weldments,a series of heat treatment conditions were performed to the circular joints welded by electron beam,and then the macrostructures and microstructures were investigated using optical microscopy,scanning electron microscopy,X-ray diffractometry,and transmission electron microscopy.The results show that the reheat cracking occurs primarily along the grain boundaries in the weld when the Ti2AlNb circular welded joints are heated up to about 700℃.During the heat treatment,an almost complete transformation of B2→O happens while the temperature goes up through the O single-phase region.Then,O→B2+O phase transformation occurs primarily along the grain boundaries as the weld metal continues to heat up to the B2+O dual-phase region.Under the high tension stress consisting of welding residual stress and phase transformation stress,reheat cracking occurs at the interface between the B2+O dual-phase layer and the O-phase matrix.
文摘The aim of the present work is to evaluate the fatigue crack growth behaviour of 12 mm thick AA 7075-T651 aluminium alloy plates joined by FSW. Fatigue crack growth test was carried out on center cracked tensile (CCT) specimens extracted from the FSW joints and unwelded parent metal. Transverse tensile properties of the unwelded parent metal and welded joints were evaluated. Microstructures of the welded joints were analyzed using optical microscopy and transmission electron microscopy. The scanning electron microscope was used to characterize the fracture surfaces. It was found that the ΔKcr of the welded joint is reduced by 10×10-3 MPa·m1/2 in comparison with the unwelded parent metal. Hence, the fatigue life of the friction stir welded AA 7075-T651aluminium alloy joints is appreciably lower than that of the unwelded parent metal, which is attributed to the dissolution of precipitates in the weld region during friction stir welding.
