Abstract: A novel solder bonding material for high-temperature applications based on Cu@Sn core-shell structured particles was developed, and the fabricated Cu@Sn particles were compressed into preforms for die attachment. The reflow temperature for this bonding material could reached as low as 260°C due to the low melting temperature of the outer Sn layer. However, after reflow soldering, the resulting interconnections can withstand a high temperature of at least 415°C, outer Sn layer completely transformed into Cu-Sn intermetallic compounds (IMCs) with high remelting temperatures. The formed bondlines exhibit good electrical conductivity due to the low porosity and the embedded Cu particles in the interconnections. Furthermore, the interconnections also exhibit excellent reliability under thermal shock cycling from-55°C to 200°C. This die attach material is suitable for power devices operating under high temperatures or other harsh environments.
Abstract: Forming limit is one of the important indexes to evaluate the formability of materials. In a variety of methods of evaluating the formability of materials, the forming limit diagram (FLD) is the most intuitive and effective, and the most widely used. There are many methods to obtain the forming limit diagram. This paper mainly introduces the methods for obtaining the forming limit diagram of the material defects, and material defects are classified into three categories: geometric defects, defects in organization structure and material constitutive defects, and the methods for obtaining forming limit diagram based on these three kinds of defects is analyzed and summarized.
Abstract: In this paper the hot behaviour of AA2017 aluminium alloy sheet was analyzed through gas blow forming tests. The material, heated and kept at a constant temperature, was subjected to gas blow forming tests under a constant pressure. Specimens with a thickness of 1.00 mm and 0.55 mm were employed. The study defines a reference value for the forming temperature as well as the hardness of the finished component. In addition, the hardness was also measured following tests conducted in several steps of the forming process.
Abstract: A three-coordinateopper (I) complex supported by N-heterocyclic carbene (NHC) ligand and bis [2-(diphenylphosphino) phenyl] ether (POP) ligand were successfully reported and characterized. The corresponding photophysical properties were investigated using UV-vis and emission spectrometry. The lowest-energy absorption band at 343 nm was assigned to metal-to-ligand charge transfer (MLCT) transtion. The emission maximum located at 470 nm upon excitation at 290 nm in PMMA films at room temperature originates from the typical 3MLCT excited state.
Abstract: The grind-hardening test of 42CrMo steel was carried out on a forming grinding machine. The macrostructure, microstructures, micro-hardness and the depth of the hardened layer were measured and analyzed by optical micro-scope, scanning electron microscope and digital micro-hardness tester. The influences of original microstructure on the grind-hardened layer of 42CrMo steel were studied. The results show that the acicular martensite and a small amount of undissolved carbide appear in the surface layer, and slightly coarse martensite and a small amount of undissolved carbide appear in the middle layer of the completely hardened zone. Microstructure of the transitional zone varies with original structure. The microstructures and micro-hardness of the completely hardened zone have no obvious change under different original organizations, and the micro-hardness is 620HV0.5-700HV0.5. However, the distance from the slightly coarse martensite and the depth of the hardened layer increase with the uniformity improvement of the original microstructure.
Abstract: In this paper, the optimization of the parameters of the isothermal forging technology to form spur bevel gear was studied. The goal of the optimization is to decrease the forming load during the process. Then, some factors included the ratio of height to diameter of billet, thickness and position of punching recess, deformation temperature and velocity were taken as the optimization values and the orthogonal experimental method was employed to carried out the optimization. After the optimization, a set of optimum technology parameters were obtained. The result demonstrates that the precise spur bevel gear can be formed with less forming load and without causing under-filling and folding defect by using the isothermal forging and choosing suitable parameter, which provides reference to form the spur bevel gear.
Abstract: This paper addresses the collective effects of aging treatment and addition of SiC particles (SiCp) on both the compression performance and corrosion behavior of Mg-10Zn-0.6Zr alloy through experimental study. The results indicate that aging treatment at 180°C for 18h while adding SiCp can improve both the compressive strength and the corrosion rate of Mg-10Zn-0.6Zr alloy. The microstructure analysis and corrosion mechanism analysis justify the effects observed. Specifically, the improvement of compressive strength is due to the fine grain strengthening and second phase strengthening. Acceleration of corrosion is attributed to two factors. The first is the precipitation of the second phase after aging treatment. The second is the morphological changes of corrosion products resulted from aging treatment and addition of SiCp.
Abstract: This paper studies the microstructure of welded joints of Q345R/304 stainless steel clad plates after high temperature ageing. E309Nb welding rod, ER310 welding wire, and ER309L welding wire were used as cladding filling materials, and ER50-6 welding wire was used as base-layer filling material for welding. The metallographic microstructure of welding joints were studied after ageing treatment at 600°C for 100 hours. Test results showed that the microstructures of cladding weld zone were austenite and ferrite, and the ferrite in cladding weld zone of ER309L welded joints is less than the one in cladding weld zone of E309Nb and ER310 welded joints. The microstructure in the fusion zone is in-continuous, and the fine ferrite is distributed on the austenite matrix. After high temperature ageing, the width of fusion zone in ER309L welded joints is obviously less than that of the other two welded joints. The toughness of ER309L welded joints is better than that of E309Nb and ER310 welded joints.
Abstract: Optimization design and simulation of the spiral selector in the process of single crystal preparation were studied. Based on the analysis of simulation and experiment results, the grain structure and orientation in different section height at starter block and spiral part have been discussed. The influence and mechanism of spiral selector parameters on the behavior of the crystal selection were proposed. The design standard of the spiral selector was put forward.