Advanced Materials Research Vols. 774-776

Abstract: 40CrNi2Si2MoVA high-strength steel is widely used in aircraft industry because of its unique combination of ultrahigh strength with high fracture toughness. However, 40CrNi2Si2MoVA is vulnerable to both corrosion fatigue and stress corrosion cracking failures with catastrophic consequences for aircraft. The high strength steel 40CrNi2Si2MoVA is enhanced and strengthen by usage of laser shock processing (LSP) with a optimal shock processing parameters, and after a series of comparion experiment in different overlap rate,the surface compressive residual stress in the testing specimen is measured and compared, and the experiment results show that the specimen surface has-962MPa compressive residual stress. Finally, the enhanced effect of compressive residual stress in surface of specimen by laser shock is discussed. The results of laser shock processing has a guiding significance to the engineering applications of high strength steel.

Abstract: Direction of flow of the liquid metal in the weld pool have important implications for weld. The liquid metal to weld edges near the point of internal flow in molten pool and the undercut could emerge when the liquid metal was freezing, by contrast, is not prone to undercut. The external magnetic fields could change the distance of surface tension of liquid metal, which may lead to the change of flow direction of molten pool. Article compares the different magnetic field under the condition of weld cross section of the timing of the welding arc. Results show that magnetic arc anode spots, TIG welding arc anode spot diameter greater than when there is no magnetic field effectively effective diameter, which will help reduce the undercut.

Abstract: Simulation experiment was done to investigate the effects of rare earth on hot-dipped Zn-55%Al alloy coating. The results show that the rare earth has little effect on the zinc dross and its burning loss is about 10%. The microstructure of coating is similar to that of solidification bath, and which is made up of phases of rich aluminum, rich zinc, rich silicon and rare earth, and intermetallic layer of Al-Zn-Fe-Si. The rare earth phase is needle or rod, and mainly distributed inside rich zinc phase and on the interface between the coating and steel substrate. The rare earth has no obvious influence on coating grain and spangle size. The appropriate addition of rare earth would be helpful to improve the coating bending formability and corrosion resistance.

Abstract: In this paper, through the analysis of 304 stainless steel to elaborate the influence of various factors in the process of drilling from the blade material,tool geometry parameters,cutting parameters and drilling methods.It is proved by selecting reasonable processing, cutting tools and cutting parameters (Φ50mm × 4700mm) 304 stainless steel parts of the drilling process issues can be resolved.

Abstract: X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (TEM) with high annular dark-field (HAADF) microscopy have been used to characterize the nanoscale oxide film formed naturally on the surface of cold-rolled sheet of mild steel. Main aim of this research was to confirm that XPS could be used in determining the thickness of thin oxide film as a substitute for the laborious TEM analysis. The preparation and analysis technique for the XPS depth profiling has been investigated to characterize the oxide film. The selection of appropriate sputter rate and sputter area according to sheet material components and the exact estimation of sputter depth from sputter rate during depth profiling were essential for the determination of the nanoscale oxide thickness.

Abstract: In the present study, process developments for net-shape forming of aluminum roof joint node have been described. These joint node parts were designed for low speed electric vehicles of which operating condition is more moderate than general compact cars. Thixoforming of Al-7%Si-0.5%Mg (A357) alloy has been applied to the net-shape forming of a complex roof joint node to support aluminum space frame structure of low speed electric vehicle. Optimum heating temperature for the A357 billet was between 580 and 585°C corresponding to the semi-solid temperatures showing 20-30% of liquid fraction. An injection speed of around 100mm/s and preheating of die at temperatures of 200~250°C were also necessary conditions to obtain reasonable thixoformed parts.

Abstract: The microstructure and mechanical properties of welded joint between 20SiMn3NiA and 40CrNiMo were studied by carbon-dioxide arc welding. According to the principle of low strength matching of dissimilar metals weld, the strength of the welded joint is 60% of that of 20SiMn3NiA, and the impact toughness reaches 60% of parent metal’s toughness. Also the impact ductility is high enough to meet the applications of divided structure tamping tine when the strength of welded joint is properly lower than that of 20SiMn3NiA. Furthermore the performances of fusion zone are worse than welded joint and heat-affected zone for martensitic brittle layer was formed during the welding of 20SiMn3NiA and 40CrNiMo.

Abstract: Friction stir welding (FSW) is a solid-state welding process where no gross melting of the material being welded takes place. Numerical modelling of the FSW process can provide realistic prediction of the thermo-mechanical behaviour of the process. Latest literature relating to finite element analysis (FEA) of thermo-mechanical behaviour of FSW process is reviewed in this paper. The recent development in thermo-mechanical modelling of FSW process is described with particular reference to two major factors that influence the performance of FSW joints: material flow and temperature distribution. The main thermo-mechanical modelling used in FSW process are discussed and illustrated with brief case studies from the literature.

Abstract: Heat flux distribution has an important influence on grinding thermal field, therefore an accurate heat flux distribution model must be established in order to precisely simulate the grinding process. A new heat flux distribution model was developed by theoretical derivation in this paper. In order to simulate the transient grinding thermal field, finite element models were created, applied with the new, uniform and triangular heat flux models respectively. Comparisons between the distributions of temperatures and temperature histories calculated from numerical simulations using the three different models were also made in this paper.

Abstract: The PCD cutting tool is used to dry mill foundry sand materials, SEM is used for observing the wear morphology of the cutting tool, and EDS is used to analyze the components of the wear area of the cutting tool so that the wear morphology of the cutting tool and the wear mechanisms are studied. The research results indicate that the wear morphology of the PCD cutting tool in cutting sand molds are rake face wear, cutting edge wear, and flank wear. The wear mechanism of the PCD cutting tool is abrasive wear, which is caused when PCD crystal particles produced in the mechanical friction between the cutting tool and the work-piece material in cutting continuously come off. Mechanical fatigue wear is the main cause of mechanical fatigue caused by alternating load which is generated by the interrupted cutting and high-frequency mechanical shock of workpiece material hard point.