Papers by Keyword: Microstructure

Abstract: The influence of the solution treatment (at the temperature of 500-520°C for 4-12 h) on microstructures and mechanical properties of Mg-Gd-Y-Zr alloy was investigated by means of optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and Vickers hardness measurement. The as-cast alloy contains a microstructure consisting of α-Mg matrix, Mg₅Gd phase and Mg₂₄Y₅ phase. With increasing solution temperature and time, the quantity of the primary particles (Mg₅Gd and Mg₂₄Y₅) in the alloy continually decreased, and the degree of recrystallization gradually increased, which result in the gradual decrease of the Vickers hardness of the solution-treated alloys.

Abstract: In this paper, AZ31B magnesium alloy/LY12 aluminum alloy were bonded together with copper foil as interlayer by vaeuum diffusion bonding technology at different temperature for holding time 60 min and pressure 2.5MPa. Analysis the microstructure of the joint under the condition of 450°C,and the effects of heating temperature on the shear thrength , microhardness and the width of the interface zone were studied. The results showed that under the condition of 450°C in holding time 60 min and pressure 2.5MPa, the microstructure at interface zone of diffusion brazing joint includes α-Mg solid solution, Mg₂Cu, Cu₂Mg, γ-Cu solid solution, CuAl, CuAl₂ and β-Al solid solution. The width of the interface increases with brazing temperature increasing, and the microhardness gradient of interface zone in the side of aluminum alloy is much higher than that in magnesium alloy side. As the welding temperature increases, the shear strength shows an increasing trend at first and then decreases. When the welding process is 460°C keeping for 60 min, welding pressure is 2.5Mpa, the highest shearing strength of the joint can reach 35 MPa.

Abstract: Experimental investigations of fatigue cracking behavior of LC9 aluminum alloy (AA LC9) subjected to elevated temperature were conducted with scanning electron microscope (SEM). Results indicate elevated temperature is important for the fatigue crack growth of AA LC9. Based on small crack growth, crack growth rate for AA LC9 is characterized.

Abstract: The effects of the thermal cycling on the coefficient of thermal expansion (CTE) and microstructure of the hypereutectic Al-Si alloys were investigated. The hypereutectic Al-Si alloy was produced by spray-forming and extruding process. Experiment results showed that the distribution of Si in Al matrix is uniform for the Al-Si alloy. The primary Si phase grew gradually during the thermal cycle. There is no remarkable change of CTE during thermal cycling for both materials at the same temperature range. The CTE of Al-Si alloy decrease with increasing on thermal cycling temperature up to 300°C due to the compressive thermal stress in the alloys.

Abstract: According to the characteristics of high strength weathering steel, this paper designs to develop anexperimental steel S450EW with yield strength higher than 450MPa.Through the study,it has been found that with decreasing cooling rate, the organizational changed largely, while ferrite and pearlite gradually transformed to martensite and a small amount of ferrite, then finally tomartensite organization.It has also been found that the crystal size decreased, and the experimentalsteel also precipitated a rectangular second phase particles of (NbTi) CN phase and TiC, which were sparsely distributed with the size of 100 ~ 300nm and below 30nm, while some phases were distributedasa number of strips in the grain boundary which mainly are C, Fe, Cr.

Abstract: Polymethylmethacrylate (PMMA) material has excellent characteristics, such as being light weight, low cost, ease of machining, and optical quality, which are useful in numerous applications such as backlit LCD display panels, lens optics, and other photoelectric fields. Laser machining of polymerization material results in a superior machining quality, high accuracy, high speed, and high reproducibility, produces a small variety of products, reduces mold costs, and enables the rapid manufacture of products based on complex graphics by processing different depths and widths of the 3D structure. This paper presents the fabrication of symmetrical array microstructures on PMMA material by using a UV laser system. The PMMA material dimensions and thickness were 20 x 20 mm and 1 mm, respectively. Regarding the machining quality, the laser pulse energy, pulse repetition frequency, and fill spacing were adjusted. For the experiments, a semiconductor laser source (635 nm/5 mW/TEM₀₀) and a beam profiler were used to measure the characteristics of a laser beam passing through the microstructures. The microstructure pitches and morphologies also affected the light uniformity. After laser machining, the surface morphology and the light transmittance were measured using a spectrophotometer.

Abstract: The challenging problems for designers and engineers in the material science are to enhance the quality of the castings. The several numbers of methods using external forces have been applied to introduce fluid flow during solidification of molten metal in casting process. These include mechanical, electromagnetic and ultrasonic vibration. Many technical journals describe the improvement in mechanical properties of castings under the vibration during solidification. In this paper, an attempt has been made to review the casting process to refine the microstructure of cast product. The awareness gain of these processes and application of the procedures offer the scope for better cost savings in design and manufacturing of cast products.

Abstract: Mg-30Ca and Mg-14Li (wt %) master alloys were melted successively in the induction furnace to obtain a Mg-Li-Ca ternary alloy containing 3.99 % Li and 1 % Ca. The as-cast material of thickness 4 mm was homogenised at 350° C for 120 mins and subsequently rolled to 62.5 % reduction in thickness at 300 °C to get 1.5 mm thick sheet. The microstructures of hot rolled samples were examined in as-rolled condition as well as after annealing at 350° C for various lengths of time. The presence of deformation twins was clearly seen in the as-rolled structure, whereas equiaxed twin-free grains were observed in the annealed condition. The average grain size was found to increase from 10 μm to 18 μm by annealing, according to the kinetics that follows a parabolic law. Tensile samples taken from rolled plate were deformed to failure at room temperature and a strain rate of 10^-4 s^-1. Ultimate tensile strength of as-rolled material increased to 213 MPa, while tensile elongation dropped to 6.5 % from the initial values of 134 MPa and 8.5 %, respectively. Annealing after rolling offered a good compromise between the enhanced tensile strength (160 MPa) and tensile ductility (9 %) suggesting viability of the proposed thermomechanical treatment as a means for enhancing both strength and ductility of Mg-4Li-1Ca alloy.

Abstract: Cold spray is now well recognized as one of the most powerful and efficient coating process because it is cost-attractive and “green”. However, this process still shows limitations to achieve coatings for highly-demanding service conditions such as those required in certain automotive and/or aircraft applications. Beyond these limitations, cold spray is expected to compete with conventional P/M routes.The present work therefore focussed on the study of damage mechanisms in cold-sprayed AISI 316L and 316L-matrix–Cu composites coatings due to high-loading conditions. Different damage mechanisms could occur depending on the content of Cu particle addition, due to changes in the response of the microstructure to the loading. These mechanisms were studied using the newly-developed “impact-sliding” test. In this test, a steel ball impacts the coating surface at a given frequency, with a fixed angle. The influence of major testing parameters was investigated.Microstructures before and after testing were studied using optical microscopy, scanning electron microscopy (SEM), and microprobe analysis in addition to 3D optical profilometry of impacted areas. Damage mechanisms were seen to be of two types, i.e. plastic deformation and wear. These resulted in decohesion of splats, formation of wear debris and formation of a layer with a tribologically-transformed structure (TTS) at the contact surface.Results showed that cold spray could be claimed to be suitable for the achievement of high-performance coatings for industrial applications provided that the coating microstructure can be controlled. This could be done using a composite approach to the coating composition.

Abstract: Effect of cold rolling on the microstructure and mechanical properties of a Fe-23Mn-0.3C-1.5Al (in wt. %) TWIP steel with an initial grain size of 24 μm was studied. Extensive deformation twinning occurred upon reduction by rolling. The volume fraction of the deformation twins attained about 0.2 at a reduction of 20%. Then, the intensity of deformation twinning gradually decreased with increasing the total rolling reduction. The average twin thickness of about 20 nm remained unchanged, although the distance between twins progressively reduced with increasing strain. The deformation banding was observed after a reduction of 60%. The thickness and volume fraction of microshear bands increased with increasing rolling reduction. The cold rolling led to significant strengthening of the steel that is accompanied by a drop on ductility. The yield stress (YS) increased from 235 MPa in the initial state to 1400 MPa after cold rolling with a reduction of 80%, whereas the elongation to failure decreased from 96% to 4%, respectively.