Advanced Materials Research Vols. 418-420

Abstract: Corrosion behavior and mechanism of 6082-T6 Al-alloy twin wire MIG welded joint under salt spray corrosion in 5 wt.% NaCl solution were investigated via laser scan confocal microscope, scanning electron microscope spectrometer and infrared spectroscope. Pitting was seen on both weld seam and the base metal resulted from Cl-. Uniform corrosion was also seen on the weld seam, grain boundaries had been corroded and approximate circular corrosion channels were observed, while evident pitting corrosion was seen in the base metal. Corrosion resistance of the base metal was better than that of the weld seam. The main corrosion products were composed of Al₂O₃, Al(OH)₃ and AlCl₃•6H₂O. Corrosion had a slight effect on the test sample's tensile strength, and serious results on the plasticity of the joints. In addition, transition from prior corrosion ductile to after corrosion hybrid brittle and ductile morphology was also found on the fracture surface.

Abstract: The joining materials of density ceramics and woven fibres would be potential value as sealing parts for thermal protection system application in aerospace field. Based on ZrO₂-Al₂O₃-SiO₂ phase diagram, the ceramics matrix and interlayer compositions were designed. Using the absorber-microwaves properties of Al-Si alloy, the joining of ZTM ceramics and fibre materials with interlayer was achieved by microwave hybrid heating method. The experiment results indicated that the interlayer ingredients were mullite, zirconia and alumina after microwave sintering. The strength of joint specimens was related with the interlayer compositions and the specimen preserved elasticity property according to the test result of universal testing machine. The joint mechanism of interlayer by microwave sintering was discussed in this paper.

Abstract: This paper describes an automation welding control system for Tungsten inert gas shielded (TIG) welding to maintain constant arc length. And using this method can replace manual operation. A voltage transducer was used to avoid high-frequency voltage. And dynamic relation between variation of arc length and voltage are described. A digital Proportion-Integration-Differentiation (PID) controller with identified value has been used modulate the rate of electrode feed mechanism. The mechanism, which driven by Servomotor A, can compensated variation of arc length in welding path. By keeping the arc length constant during the welding process, an elegant appearance and higher quality seam is obtained. The experiment result shows that this automatic control system based on digital PID controller is stable, and can working effectively without operator manipulation.

Abstract: The objective of this work was the development of a technology for the fabrication of piezoelectric PZT thin films from bulk PZT on silicon wafer for micro power harvester applications. With the lapping technique, the thickness of bulk PZT was reduced from 300µm to 10µm at the top data. KOH etching for silicon was used to thin the thickness of silicon cantilever from 300µm to 15µm at the top data. The piezoelectric coefficient d₃₁ was measured to be -12pC/N. Resonance frequency measurements on a 4mmX1mmX0.06mm cantilever resulted in a value of 430Hz, and the voltage output was around 0.68V at 1g acceleration. The result shows that the fabrication process is quite feasible.

Abstract: A ~1.2 meter long trough comprising of variable cross-sections, with the highest ratio of depth to opening width reaching 1.4, is gas-formed at 500°C with superplastic aluminum alloy 5083. It is a challenge to successfully make such an industrial scale part as demonstrated in this paper. Starting as an expanded V-shaped groove, pressurized gas is manipulated to flow into the forming die, and the pressure vs. time profile needs to be calculated. Thus, the flow stress in the deforming material is optimal to maintain desired strain rate correspondingly. Thickness distribution over the formed product is far from uniform. The other even undesired result is that the thinnest region suffers severe cavitation

Abstract: The electrochemical behavior of welded joints with 308L stainless solid welding wire and low temperature transformation welding wire using different welding processes was investigated at ambient temperature in 3.5% NaCl solution using potentiodynamic polarisation technique. Welded joints exhibited different corrosion potential due to the dilutions of alloy elements such as Cr, Ni, Ti, Nb and Mo. To reveal the corrosion resistance of welded joints using different welding processes, some significant characterization parameters such as E_corr, E_b, △E and I_corr in polarisation curves were analyzed and compared. The result shows that the corrosion resistance of welded joints using low temperature transformation welding wire is better than that using 308L stainless solid welding wire.

Abstract: Abstract. The microstructure and mechanical properties of a metal inert gas welds in a medium strength Al-4Zn-1Mg alloy were characterized by optical microscope (OM), scanning electron microscope (SEM) and tensile tests. It is found that the joint of the alloy contained three distinctive regions, i.e. fusion zone, heat affected zone and base metal region. Extensive microhardness measurements were conducted in the weld regions of the nuggets exhibited a hardness loss in the fusion zone due to the loss of strengthening phases. Microstructural examination of the joints revealed typical eutectic structure was appeared in the heat-affected zone. Tensile properties of the joints were obtained by testing flat transverse tensile specimens, and the results indicated that tensile strength of these welds approached 83.3~84.2% of the base metal.

Abstract: A kind of severe deformation method for refined grain materials named continuous variable cross-section recycled extrusion (CVCE) was proposed. The composition structure and working principle of processing were introduced. First, the cylinder specimen was extruded to circular cone and then the circular cone specimen was compressed into columned one. After that, the specimen was rotated by 180° and repeated the forward procedure. All of procedures mentioned above constitute a cycle. The whole process is repeated again and again. The process can introduce ultra-high plastic strain without any geometrical change. The process has been applied to commercial aluminum (1100), Mg alloy. After several cycles of CVCE, bulk materials with sub-micron grain structure were successfully obtained. The average grain size of AZ31 magnesium alloy is refined from 25μm to 3μm after six cycles and the tensile elongation were improved dramatically.

Abstract: Micro-EDM is a flexible process which has many technique methods such as forming, drilling, milling, copying and WEDM. Combined these methods together can enhance the EDM machining ability. In this paper a set of route design regulations used in combined machining is proposed. Through these regulations, the optimal route of combined process can be obtained which can improve high machining quality and efficiency. To test performance of the regulations, the combined route of a micro part is designed and its fabrication is performed at last.

Abstract: Deep drawing is one of the sheet metal forming processes used widely in industries like automobile, aerospace etc. In drawing operation, the limiting draw ratio (LDR) is used as an index of drawability of a material. In this investigation, stainless steel AISI 304 grade blanks of 1.0 mm thickness with different diameters are drawn into a circular cups in single stage. The experiments were conducted at room temperature as well as at temperatures 100oC, 200oC, and 300oC. The LDR values obtained in each condition were analyzed. The experimental results show that there is a significant improvement in LDR values by warm working.