Enhancement of the Al/Mg Dissimilar Friction Stir Welding Joint Strength with the Assistance of Ultrasonic Vibration

The assistance of ultrasonic vibration during the friction stir welding (FSW) process has been verified as an effective approach for the improvement of joint strength. In the present study, experimentation on Al/Mg dissimilar alloys in butt joint configuration is implemented by employing FSW with and without the assistance of ultrasonic vibration. An optimized tool shoulder diameter of 12 mm is utilized, and the ultrasonic vibration is applied perpendicularly onto the tool along the welding direction, which is named UVaFSW. The results of joint appearance and macrostructure, characteristics of the intermetallic compounds (IMCs), as well as joint strength and fracture appearance are compared between Al/Mg FSW joints with and without ultrasonic vibration. It is demonstrated that the material intermixing between Al and Mg alloys is substantially strengthened in the UVaFSW joint compared with that in the FSW joint. Additionally, the ultrasonic vibration can be beneficial for the reduction of IMC thickness, as well as the formation of intermittently distributed IMC phases at the Al–Mg bonding interface. Consequently, the mechanical properties of Al/Mg FSW joints are significantly improved with the assistance of ultrasonic vibration. The maximum ultimate tensile strength is 206 MPa at tool rotation speed of 800 rpm and welding speed of 50 mm/min for the Al/Mg UVaFSW joint.

Microstructure and Mechanical Properties of Tempered Ausrolled Nanobainite Steel

The microstructures and mechanical properties of ausrolled nanobainite steel, after being tempered at temperatures in the range of 200−400 °C, were investigated in this study. After being tempered, bainitic ferrite is coarsened and the volume fraction of retained austenite is reduced. The hardness and ultimate tensile strength decrease sharply. The impact energy, yield strength, and elongation increase with elevated tempered temperature at 200–300 °C but decrease with elevated tempered temperature when the samples are tempered at 350 °C and 400 °C. The fracture appearance of all the samples after impact tests is a brittle fracture. The variation of the mechanical properties may be due to partial recovery and recrystallization.

Comparative Analysis of Macro- and Microstructure of Printed Elements in the FDM, SLS and MJ Technologies

The article presents research conducted with the project: ‘Additive manufacturing in conduction with optical methods used for optimization of 3D models’’ [2]. The article begins with the description of properties of the materials used in three different additive technologies – Fused Deposition Modelling (FDM), Selective Laser Sintering (SLS) and Material Jetting (MJ). The next part focuses on the comparative analysis of macro- and microstructure of specimens printed in order to test selected materials in additive technologies mentioned above. In this research two types of specimens were used: dumbbell specimens and rectangular prism with hole specimens. In order to observe macrostructure specimens, they were subjected to load test until it broke. In the case of observing microstructure, they were cut in some places. Each of described additive technologies characterizes by both different way of printing and used materials. These variables have a significant influence on macro- and microstructure and fracture appearance. FDM technology specimens printed of ABS material characterized by texture surface appearance. SLS technology specimens printed of PA12 material characterized by amorphous structure. MJ technology specimens printed of VeroWhite Plus material characterized by fracture appearance which had quasi- fatigue features. The microstructure of these specimens was uniform with visible inclusions.

Pearlite Spheroidization and Its Relationship with Tensile Strength in Hypoeutectoid Steels

One steel containing 0.6 wt pct C, 0,78 wt pct Mn, and 0.32 wt pct Cr was austenitized at 840 °C for 1 hour and cooled at two rates. Microstructural evaluation by light optical and scanning electron metallography showed a change in the pearlite microstructure. Cooling in air as compared to furnace cooling reduced the pearlite interlamellar spacing and increased the hardness. The slower cooling resulted in a lower tensile strength, higher tensile elongation, and a different fracture appearance.

Simulation Analysis of In-Plane Compression on Three-Dimensional Spacer Fabric Composite

A meso-structure model of three-dimensional spacer fabric composite (3D composite) was built by using the finite element software Workbench, and simulation analysis of in-plane compression on the 3D composite was studied according to the model. The results show that the upper and lower face-sheet is the main load-bearing section macroscopically, while the piles are the secondary load-bearing one when the 3D composite is subjected to in-plane compressive load. The fibers play a major role microscopically, while the resin plays a minor one. From part magnifying stress distribution, it can be found that the maximum stress occurs in the warp yarns, interlaced with weft yarns, when the 3D composite is subjected to in-plane compressive loads in warp direction, and fracture appearance is parallel. Meanwhile, the maximum stress occurs in the weft yarns, interlaced with binder warp yarns, when the 3D composite is subjected to in-plane compressive loads in weft direction, and fracture appearance is random. From strain distribution of each component, it can be seen that the failure mode is the interfacial de-bonding between the fibers and resin when the 3D composite is subjected to in-plane compressive loads.

Effect of PWHT Conditions on Toughness and Creep Rupture Strength in Modified 9Cr-1Mo Steel Welds

We clarified the effect of post weld heat treatment (PWHT) conditions on the toughness and creep rupture strength of modified 9Cr–1Mo steel weldments used for high temperature components of ultra-supercritical power plants. Fracture appearance transition temperature (FATT) decreased as PWHT temperature increased, and for all of the weld metals of tungsten inert gas welding, submerged arc welding and shielded metal arc welding, FATTs were lower than 293 K when the PWHT temperature was higher than 1,008 K. In contrast, in the uniaxial creep test with a loaded stress of 108 MPa, the creep rupture strength of the specimen on which PWHT was carried out for a holding time of 7.2 ks was significantly decreased when the PWHT temperature was more than 1,033 K. Therefore, the appropriate PWHT temperature range to maintain the toughness and creep fracture strength was 1,008 K ≤ T ≤ 1,033 K.

The effect of mean axial and torsional stresses on the fatigue strength of 34CrNiMo6 high strength steel

The present study consists of a theoretical, experimental and fractographic investigation of the effect of superimposed static axial and shear stresses on the high cycle fatigue behavior of a 34CrNiMo6 high strength steel in quenched and tempered condition (UTS = 1210 MPa), commonly employed in highly stressed mechanical components. The Haigh diagrams for the axial and torsional cases under different values of mean stress were obtained. In both cases, experimental results showed that increasing the mean stress gradually reduces the stress amplitude that the material can withstand without failure. The results of the present tests are compared with the theoretical predictions from Findley, based on the maximum damage critical plane; and the methods of Marin and Froustey, which are energetic based criterions. Froustey’s method shows the best agreement with experimental results for torsional fatigue with mean shear stresses, showing a non-conservative behaviour for the axial fatigue loading case. Macro-analyses and micro-analyses of specimen fracture appearance were conducted in order to obtain the fracture characteristics for different mean shear stress values under torsion fatigue loading.

Impact Toughness of Gas Metal Arc Welded HY-80 Steel Plate at Sub-zero Temperatures

Various welding methods are widely applied in large fabrication of high strength steel. However, commonly the problem occurs where a coarse grain is formed near fusion zone causing reduce the impact toughness due to the weld joint become brittle. Ductility and toughness in a coarse grain heat affected zone (CGHAZ) is low due to the formation of coarsening grain size. The objective of this research is to investigate the microstructure evolution, impact toughness and fracture appearance at sub-zero temperatures of the high strength steel arc welded. The steel that used in this experiment is a HY-80 steel welded by gas metal arc welding (GMAW) with a mixture of argon and carbon dioxide (90%Ar and 10%CO2) and ER100S solid wire. Microstructure observation and Charpy V-notch (CVN) tests were performed on the weld joint which consist of base metal (BM), heat affected zone (HAZ), and weld metal (WM). The CVN tests on the HY-80 steel plate at various temperatures (20, -20, -60 and -80 °C) show impact toughness decrease when the test temperature decrease. The CVN tests on the HY-80 weld joint at a temperature of 80 °C show the lowest impact toughness was measured at WM (61 J) and followed fusion line-FL (101 J) with brittle fracture appearance.