Materials Science Forum Vol. 889

Abstract: This paper reports observation of material flow in friction-stir forming of aluminum alloy gear racks. Friction-stir forming was newly developed by Nishihara and is dedicated for material forming. In the process, a material plate is placed on the die and friction stirring is conducted on its back surface. The material deforms due to high pressure and heat caused by the friction-stir process and deforms precisely to the shape of the die. The process has mainly been studied for microforming and mechanical jointing; however it was successfully utilized for net-shape forming of A5083 aluminum alloy gear racks. The authors observed the appearance of products, change of mark-off lines on its surface, and deformation of its longitudinal cross section by photo-processing. In addition, we evaluated the distribution of hardness in transverse cross sections of a product tooth. As a result, it was observed that the material did not flow in the transverse direction of the cavity of the gear-rack die, though more material filled at the retreating side than at the advancing side. The material filled the tooth-cavity mostly before passage of the tool probe over the tooth.

Abstract: This paper deals with friction properties and deformation resistance during hot forming of Mg-Al-Ca-Mn series magnesium alloys. Friction coefficients between dies and magnesium alloys were obtained by ring compression tests that used graphite, PTFE, and an oil lubricant in a hot-forging process. Hot forging was performed under various conditions to clarify the effects of types of lubricants and slide motion of the press machines on friction properties. Two types of slide motion, a constant velocity motion and a pulse motion were selected in the ring-compression test. It was found that graphite with an oil lubricant effectively eliminated die sticking in hot forming of magnesium alloys. The isothermal deformation resistances were derived using friction coefficients obtained by ring-compression tests as well as finite-element simulations. The predicted stress strain curves with temperature were examined with the stress-strain relationship obtained in experiments using a servo press and demonstrated the effectiveness of the proposed method.

Abstract: Statistic analyses of industrial experimental datum were done to investigate the effect of pretreatment process, hot-dip process and posttreatment process on spangle size of hot-dip 55%Al-Zn alloy coated steel sheet. The results show that, with the decrease of concentration of degreasing solution, the decrease of RTF dew point temperature, the decrease of temperature at which strip entering into Al-Zn bath, and the increase of injection pressure of air knife, spangle size decreases; with the increase of hydrogen content in RTF, spangle size decreases firstly and then tends to be stable; with the increase of bath temperature, spangle size increases firstly and then decreases; The hot-dip time, the distance between air knife and steel strip, the height of air knife from Al-Zn bath, and the blowing rate of cooling fan have little effect on spangle size; the addition of mixed rare earth doesn’t affect spangle size, while the addition of titanium with trace amount leads to the decrease of spangle size.

Abstract: Bronze especially tin bronze is mostly used as material of traditional music instrument such as gamelan, cymbals, or bells. Casting process becomes an important process in making gamelan. Solidification is the most important process in the casting. This study is designed to evaluate variant of solidification rate on casting process of conventional bronze (tin bronze) as gamelan material. This study aimed at finding variant of Dendrite Arm Spacing (DAS) on acoustical characteristic of bronze alloy. The alloy of Cu–20Sn is chosen as the composition of tin-bronze because this composition is widely used as the gamelan material. Variant of solidification rate is designed by varying mold temperature and casting temperature. The bronze is melted in crucible furnace until 1050, 1100, 1100oC. Then, the melted material was poured into the mold in 400°C temperature. This study showed that increase of casting temperature influence the decrease of solidification rate which affecting the longer time of solidification. The difference of solidification rate affected on the construction of micro structure and the dendrite (DAS) formed. The size of the dendrite forms affected the mechanical and acustical tin bronze.

Abstract: Duplex Stainless Steel (DSS) combines good mechanical strength and ductility with moderate to good corrosion resistance in a variety of environments. DSS are prone to the formation of various intermetallic phases (σ, χ, π, R), carbides (M23C6) and nitrides (Cr2N), when it exposed to temperatures lower than 1000°C. This study focuses on effect of secondary phase precipitation on impact toughness of ASTM A182 DSS. Cylindrical bar of DSS was open die forged in the temperature range of 1200-1050°C. After the forging, the bar was slow cooled by covering it with ceramic wool. This leads to the formation of σ phase at the ferrite/austenite interfaces and significantly reduced the impact toughness of the material. Solution treatment was done at different temperature and effect on toughness studied. The microstructural changes produced as consequences of the distinct test condition have been analyzed by means of optical and electron microscopy, X-ray diffraction.

Abstract: The influence of excess Mg on the Mode I propagation of fatigue crack was examined in newly developed precipitation-hardened Al alloy containing Zr and excess Mg. The aim of this study was to evaluate the underlying factor affecting fatigue crack growth rate in the stage II region. For this purpose, the rotating bending fatigue tests were performed in constant amplitude loading, and replication technique with an optical microscope was used to measure the crack growth in the Al alloys. Through analyses of the crack propagation on the specimen surface and striation formation of the fracture surface, the effects of excess Mg in the Al alloys were clarified to promote the occurrence of mode I fatigue crack, and decelerate the fatigue crack propagation. These facts suggest that the dynamic strain aging of Mg induces the formation of fatigue striation and reduce the driving force of the crack propagation. The findings were supported by the fractographic observations in the fatigue crack propagation region.

Abstract: Permanent mould casting was used as the production technique to produce the metal matrix composites (MMCs) specimens. Thermal measurements during the casting process were recorded. Based on these data, solidification graphs were plotted to understand the solidification characteristics. Solidification analysis was performed by interpreting the parameters drawn from the solidification graphs. Parameters such as; nucleation primary alpha phase temperature, liquidus arrest temperature, eutectic growth temperature and solidification time were identified. The results showed that addition of titanium carbide particulates (TiCp) into the aluminium-11.8% silicon alloy (LM6) have affected various time and temperature parameters of its solidification properties. These in turn will have an influence on the mechanical property of the MMCs.

Abstract: Stainless steel was used for many engineering applications. The optimum parameters needs to be identify to save the cutting tool usage and increase productivity. The purpose of this study is to develop the surface roughness mathematical model for AISI 304 stainless steel when milling using TiN (CVD) carbide tool. The milling process was done under various cutting condition which is cutting speed (1500, 2000 and 2500 rpm), feed rate (0.02, 0.03 and 0.04 mm/tooth) and axial depth (0.1, 0.2 and 0.3 mm). The first order model and quadratic model have been developed using Response Surface Method (RSM) with confident level 95%. The prediction models were comparing with the actual experimental results. It is found that quadratic model much fit the experimental result compare to linear model. In general, the results obtained from the mathematical models were in good agreement with those obtained from the machining experiments. Besides that, it is shown that the influence of cutting speed and feed rate are much higher on surface roughness compare to depth of cut. The optimum cutting speed, feed rate and axial depth is 2500 rpm, 0.0212 mm/tooth and 0.3mm respectively. Besides that, continues chip is produced at cutting speed 2500 rpm meanwhile discontinues chip produced at cutting speed 1500 rpm.

Abstract: A slurry aluminising process was utilised to produce duplex Si-modified aluminide MCrAlY coatings for superalloy GTD-111. MCrAlY coating was applied by means of high velocity oxy-fuel (HVOF) metal spray technique. Cyclic oxidation behaviour of the aluminide/MCrAlY coating were compared with plain MCrAlY coating. Oxidation performance of the coated samples was investigated by exposing samples to 1 h cyclic oxidation at 1100 ^°C. Oxidation test results demonstrate the Si-aluminide/MCrAlY coating exhibited much better oxidation resistance than the the uncoated superalloy due to the superior oxidation resistance of the alumina-silica scale at 1100 ^°C.

Abstract: Recently, Ni-free shape memory Ti-based alloys (composed of the biocompatible β-stabilizing elements such as Ta and Nb) are extensively studied. In this work, new Ni-free Ti-17Nb-6Ta is presented as a candidate for shape memory alloys with high biocompatibility. This alloy produced using arc-melting in argon atmosphere, followed by solution annealing at 900° C for 30 min. β-phase is the predominant phase beside α” martensite phase. Stress induced martensitic transformation is observed after cold rolling and during bending tests as measured by XRD. The hardness of the bended wire in the solution treated condition was around 330HV. While the cold rolled wire hardness before bending was 300 HV. The superelasticity and shape memory effect was investigated through bending tests of alloy wires. The cold rolled wire showed higher superelasticity than shape memory effect. But superelasticity and the shape memory effect were almost similar with the solution treated wire. Also, the total spring back in cold rolled wire is higher compared with solution treated wire.