Hongchao Ji

Shut-off valve bodies are widely used in the petrochemical industry. When oil wells require maintenance or in emergency situations (such as signs of a blowout), these valves can rapidly seal off oil and gas pathways, preventing uncontrolled spills and ensuring personnel and equipment safety. Based on the shape characteristics of this shut-off valve body, a multidirectional forging process was designed. Deform software was employed to numerically simulate the forging process, analyzing the distribution patterns of deformation, temperature, strain, stress, dynamic recrystallization (DRX), and forging load (FL). Response surface optimization was conducted for temperature, punch speed, and friction coefficient, using FL and DRX volume fraction as evaluation metrics. Finite element simulation results indicate that applying the optimized process parameters to forging production yields forgings with excellent forming quality. Forging experiments demonstrate that under the optimized parameters, the forgings exhibit complete forming with no significant defects. Furthermore, their mechanical properties meet product requirements, providing theoretical guidance for the multidirectional forging process of valve bodies.

Bi-doped low-silver Sn-Ag-Cu solders are increasingly gaining attention in advanced electronic packaging due to their cost-effectiveness and enhanced mechanical properties. However, the thermo-mechanical reliability mechanisms of such modified solders, particularly Sn-0.3Ag-0.7Cu-3Bi (SAC0307-3Bi) within Ball Grid Array (BGA) assemblies, remain insufficiently understood. To address this gap, this research proposes a comprehensive assessment framework integrating constitutive parameter calibration with finite element analysis (FEA) to accurately characterize the mechanical behavior and fatigue durability of SAC0307-3Bi solder joints under cyclic thermal loads. The Anand viscoplastic parameters were first calibrated via the Norton creep law and virtual tensile tests. Subsequently, a 3D quarter-symmetry model was constructed to replicate thermal cycling conditions between 25 °C and 125 °C. Simulation data reveal a strong correlation between stress concentration and the Distance to Neutral Point (DNP), pinpointing the chip-side interface of the corner joint as the critical failure site. Moreover, creep strain was observed to accrue in a “step-wise” pattern, predominantly during the heating and cooling ramps, reflecting distinct temperature sensitivity. Utilizing the Syed model, the fatigue life was estimated at approximately 2239 cycles. These insights serve as a crucial benchmark for designing robust packages using Bi-doped, low-silver lead-free solders.

Stainless steel/carbon steel (SS/CS) composite plates find wide application in large-scale equipment such as hot blast furnaces, where the strength of welded joints constitutes a critical factor affecting structural stability and safety. Utilising ABAQUS software, a thick-plate multilayer multi-pass welding finite element model was established, incorporating the “element birth and death technique” and employing FORTRAN programming to develop the DFLUX subroutine for simulating the volumetric heat flux distribution of a double ellipsoidal heat source. This study systematically investigates the quantitative relationship between different welding procedure parameters and the mechanical properties of composite joints. By integrating response surface methodology (RSM) into a multilayer, multi-pass welding numerical simulation framework, the requirement for costly and time-consuming full-factorial parametric simulations is substantially reduced. This approach achieves multi-objective optimisation of the welding procedures for both the transition layer and cladding. Residual stress distribution analysis demonstrates high agreement between finite element simulation data along characteristic paths and experimental measurements obtained via X-ray diffraction (XRD). Metallographic analysis combined with selective etching reveals sound metallurgical bonding at the joint interface. Tensile testing confirms that the welded joint strength of the composite plate meets engineering application requirements and exhibits favourable structural load-bearing capacity. Fracture morphology analysis indicates uniformly distributed equiaxed dimples on the 904L steel fracture surface, while the Q345R steel side exhibits characteristic fibrous shear dimples.

This study examined microstructural degradation processes in three metallurgical regions of carbon-manganese steel (Q345R) welded joints—weld zone (WZ), heat-affected zone (HAZ), and base metal (BM)—utilized in hot blast stove shell fabrication under marine atmospheric exposure conditions. Cyclic salt spray accelerated corrosion tests were combined with microstructure analysis, corrosion kinetics, morphology characterization (scanning electron microscopy, energy dispersive spectroscopy, and x-ray diffraction [XRD]), and electrochemical tests to investigate the differences in corrosion behaviors among these regions. The results revealed significant microstructural heterogeneity: the WZ was dominated by massive proeutectoid ferrite and acicular ferrite; the HAZ exhibited a Widmanstätten structure; and the BM displayed a ferrite-pearlitic band structure. Microstructural defects combined with residual stresses result in markedly lower corrosion resistance of WZ and HAZ compared to BM. The kinetics of corrosion in all three regions follows a power function law, progressing through four distinct stages: rapid increase, rapid decrease, slow increase, and slow decrease. Morphological characterization revealed that the BM surface undergoes gradual changes without evident pitting, whereas cracks and porous corrosion products gradually formed in the WZ and HAZ. XRD analysis identified FeOOH and Fe3O4 as the dominant corrosion products. Electrochemical tests demonstrated that the WZ exhibits the most negative open-circuit potential and the highest corrosion current density, surpassing those of the BM and HAZ. The absence of passivation capability further confirmed the poorest corrosion resistance of the WZ. Impedance spectra corroborate that the BM rust layer possessed higher resistance and enhanced protectiveness compared to the WZ.