Tensile fracture behaviors of thixocast, artificially aged thixocast （thixocast＋T6） and as-extruded AA7075 alloys were investigated. The microstructural and fractographic observations were carried out using optical...Tensile fracture behaviors of thixocast, artificially aged thixocast （thixocast＋T6） and as-extruded AA7075 alloys were investigated. The microstructural and fractographic observations were carried out using optical microscope （OM） and scanning electron microscope （SEM）. Experimental studies showed that as-extruded and thixocast＋T6 specimens exhibited considerably more excellent mechanical properties than as-thixocast AA7075 specimen. T6 artificial heat treatment with prolonged solution treatment significantly improved the tensile properties of the thixocast AA7075 alloy. The tensile properties of as-extruded and thixocast＋T6 specimens were close to each other. In as-thixocast specimen having remarkable micro-cracks, fracture was intergranular brittle type. The ductile fracture surfaces were observed in as-extruded and thixocast＋T6 specimens. In as-thixocast specimens, decohesion started between the eutectic-matrix interfaces and propagated through grains. Micro-void coalescence was the dominant form of fracture in thixocast＋T6 heat treated specimens. The micro-voids nucleation was initiated at the interface between the matrix and multinary eutectic structure.展开更多
This study investigates the cryogenic tensile properties and fracture behavior of fiction stir welded and post-weld heat-treated joints of 32Mn-7Cr-1Mo-0.3N steel. Cryogenic brittle fracture, which occurred in the as-...This study investigates the cryogenic tensile properties and fracture behavior of fiction stir welded and post-weld heat-treated joints of 32Mn-7Cr-1Mo-0.3N steel. Cryogenic brittle fracture, which occurred in the as-welded joint, is related to the residual particles that contain tungsten in the joint band structure. Post-weld water toughening resulted in the cryogenic intergranular brittleness of the joint, which is related to the non-equilibrium segregation of solute atoms during the post-weld water toughening. Annealing at 55OC for 30rain can effectively inhibit the cryogenic intergranular brittleness of the post- weld water-toughened joint. The yield strength, ultimate tensile strength, and uniform elongation of the annealed joint are approximately 95%, 87%, and 94% of the corresponding data of the base metal.展开更多
2D carbon fiber reinforced AZ91 D matrix composites（2D-C_f/AZ91 D composites） were fabricated by liquid–solid extrusion and vacuum pressure infiltration technique（LSEVI）. In order to modify the interface between ...2D carbon fiber reinforced AZ91 D matrix composites（2D-C_f/AZ91 D composites） were fabricated by liquid–solid extrusion and vacuum pressure infiltration technique（LSEVI）. In order to modify the interface between fibers and matrix and protect the fiber, pyrolytic carbon（Py C） coating was deposited on the surface of T700 carbon fiber by chemical vapor deposition（CVD）. Microstructure observation of the composites revealed that the composites were well fabricated by LSEVI. The segregation of aluminum at fiber surface led to the formation of Mg_（17）Al_（12） precipitates at the interface. The aluminum improved the infiltration of the alloy and Py C coating protected the fibers effectively. The ultimate tensile strength of 2D-C_f/AZ91 D composites was about 400 MPa. The fracture process of 2D-C_f/AZ91 D composites was transverse fiber interface cracking–matrix transferring load–longitudinal fibers bearing load–longitudinal fibers breaking.展开更多
基金the financial supports of the State Planning Organization of Turkey (DPT Project Number: 2003K120470-27)Gazi University Scientific Research Fund (GUBAP Project Number: 07/2013-01)
文摘Tensile fracture behaviors of thixocast, artificially aged thixocast （thixocast＋T6） and as-extruded AA7075 alloys were investigated. The microstructural and fractographic observations were carried out using optical microscope （OM） and scanning electron microscope （SEM）. Experimental studies showed that as-extruded and thixocast＋T6 specimens exhibited considerably more excellent mechanical properties than as-thixocast AA7075 specimen. T6 artificial heat treatment with prolonged solution treatment significantly improved the tensile properties of the thixocast AA7075 alloy. The tensile properties of as-extruded and thixocast＋T6 specimens were close to each other. In as-thixocast specimen having remarkable micro-cracks, fracture was intergranular brittle type. The ductile fracture surfaces were observed in as-extruded and thixocast＋T6 specimens. In as-thixocast specimens, decohesion started between the eutectic-matrix interfaces and propagated through grains. Micro-void coalescence was the dominant form of fracture in thixocast＋T6 heat treated specimens. The micro-voids nucleation was initiated at the interface between the matrix and multinary eutectic structure.
基金Financial support by State Key Lab of Advanced Welding and Joining,Harbin Institute of Technology
文摘This study investigates the cryogenic tensile properties and fracture behavior of fiction stir welded and post-weld heat-treated joints of 32Mn-7Cr-1Mo-0.3N steel. Cryogenic brittle fracture, which occurred in the as-welded joint, is related to the residual particles that contain tungsten in the joint band structure. Post-weld water toughening resulted in the cryogenic intergranular brittleness of the joint, which is related to the non-equilibrium segregation of solute atoms during the post-weld water toughening. Annealing at 55OC for 30rain can effectively inhibit the cryogenic intergranular brittleness of the post- weld water-toughened joint. The yield strength, ultimate tensile strength, and uniform elongation of the annealed joint are approximately 95%, 87%, and 94% of the corresponding data of the base metal.
基金supported by the National Nature Science Foundation of China (Nos. 51472203, 51521061, 51575447 and 51432008)
文摘2D carbon fiber reinforced AZ91 D matrix composites（2D-C_f/AZ91 D composites） were fabricated by liquid–solid extrusion and vacuum pressure infiltration technique（LSEVI）. In order to modify the interface between fibers and matrix and protect the fiber, pyrolytic carbon（Py C） coating was deposited on the surface of T700 carbon fiber by chemical vapor deposition（CVD）. Microstructure observation of the composites revealed that the composites were well fabricated by LSEVI. The segregation of aluminum at fiber surface led to the formation of Mg_（17）Al_（12） precipitates at the interface. The aluminum improved the infiltration of the alloy and Py C coating protected the fibers effectively. The ultimate tensile strength of 2D-C_f/AZ91 D composites was about 400 MPa. The fracture process of 2D-C_f/AZ91 D composites was transverse fiber interface cracking–matrix transferring load–longitudinal fibers bearing load–longitudinal fibers breaking.
