Materials Science Forum Vol. 1042

Abstract: Dissimilar metal lap joining of A5052 aluminum alloy plate and C1100 pure copper plate was performed by using friction stir spot welding. The rotating welding tool, which was composed of a probe part and a shoulder part, was plunged from the aluminum alloy plate which was overlapped on the copper plate, and residual aluminum alloy thickness under the probe part of the welding tool after plunging of the welding tool was controlled in the range from 0 mm to 0.4 mm. The strength of the welding interface was evaluated by using tensile-shear test. Microstructure of the welding interface was examined by using an optical microscope and a field emission scanning electron microscope. The welding was achieved at the residual aluminum alloy thickness under the probe part of the welding tool below 0.3 mm. The welded area was formed at aluminum alloy/copper interface located under the probe part of the welding tool, and its width increased with decreasing the residual aluminum alloy thickness. A characteristic laminate structure was produced in the copper matrix near the welding interface. In the joint fabricated at the residual aluminum alloy thickness below 0.1 mm, hook of Cu was formed at edge of the welded area. The fracture did not occur at the welding interface. A remarkable improvement in strength was observed in the joint fabricated at the residual aluminum alloy thickness below 0.1 mm. The formation of laminate structure and hook is considered to result in joint strength improvement.

Abstract: Thermally-induced phase transformation (PT) is of significance and value to the application of NiTi alloy components. Low-temperature aging (LTA) treatment was used to alter PT characteristics of NiTi alloys avoiding undesirable grain growth. Effect of LTA on PT of NiTi wires with a wide range of grain sizes from 34 nm to 8021 nm was investigated in this study. As the average grain size varies from 34 to 217 nm, the temperature of the B2↔R transformation increase as a result of LTA, and the increasing effect is more obvious at a larger grain size. For NiTi alloys with average grain sizes ranging from 523 to 1106 nm, transformation sequence changes from B2↔B19' to B2↔R due to LTA. For the sample with an average grain size of 2190 nm, the B2↔B19' transformation is replaced by B2↔R←B19' after LTA. When the average grain size is larger than 2190 nm, transformation sequence changes from B2↔B19' to B2↔R↔B19' after LTA. Transmission emission microscope observations reveal that the above-mentioned PT behavior correlates with the coupled effect of grain size and precipitation. The precipitation of Ni₄Ti₃ in the grains with a size smaller than ~150 nm is inhibited after LTA, the temperature of B2→R of samples with average GS smaller than ~150 nm still is elevated due to the inhomogeneous grain size of NiTi wires.

Abstract: Throughout the combination of unique approaches on innovative polymer composites and rotational moulding plastics processing technique, we developed a building block using a mix of recycled and virgin plastic. This block was a technical case study from a multidisciplinary approach - comprising materials science, polymers processing and design - to reinsert recycled plastics in the Circular Economy. The aim was to produce a three-dimensional interlockable block, combining unique design and unconventional materials to create an emblematic building element. We investigated the composition and availability of local plastic waste, as well as other waste-stream materials – concrete waste, red mud, hemp fibre, sugarcane bagasse. We prepared a range of composites and blends to test their prospective aspect and processability. To simulate the end-result of a rotationally-moulded part, we prepared samples of the blends in an oven. The thermal analysis showed that all materials were thermally stable at the processing temperature of the virgin polymer in rotomoulding, around 200 °C. There were an evident LLDPE continuous-phase and a recyclate dispersed-phase. We also explored the aesthetic effect of scattering particles of colour in the mixes. The impact test showed better results for the polyethylene-based recyclates if compared to polypropylene and poly (ethylene terephthalate) ones. We concluded that waste materials could be revalued into something practical and reproducible, produced by rotational moulding plastics processing. And we developed a viable and innovative potential product for the Circular Economy, requiring minimal fixing and no further external finishing.

Abstract: Additive manufacturing (AM) technologies have been evolved over the last decade, enabling engineers and researchers to improve functionalities of parts by introducing a growing technology known as multi-material AM. In this context, fused deposition modeling (FDM) process has been modified to create multi-material 3D printed objects with higher functionality. The new technology enables it to combine several types of polymers with hard and soft constituents to make a 3D printed part with improved mechanical properties and functionalities. Knowing this capability, this paper aims to present a parametric optimization method using a genetic algorithm (GA) to find the optimum composition of hard polymer as polylactic acid (PLA) and soft polymer as thermoplastic polyurethane (TPU 95A) used in Ultimaker 3D printer for making a rectangular sample under flexural load in order to minimize the von Mises stress as an objective function. These samples are initially presented in four deferent forms in terms of composition of hard and soft polymers and then, after the optimization process, the final ratio of each type of material will be achieved. Based on the volume fraction of soft polymers in each sample, the equivalent topologically-optimized samples will be obtained that are solely made of single-material PLA as hard polymer under the same flexural load as applied to multi-material samples. Finally, the structural results and manufacturability in terms of the generated support structures, as key element of some AM processes, will be compared for the resultant samples created by two methods of optimization.

Abstract: Hard-facing is one of processes for repairing metallic surface of equipment or parts of machinery that are lost due to outworn mechanism. Therefore, hard-facing requires suitable variables to obtain the hardest hard-faced metals. This research aimed to study influence of welding speed on hard-facing affecting microstructure and hardness of the hard-faced metals on JIS-S45C carbon steel with MIG welding. According to the experiment, hard-facing with welding speed at 250 mm/min contained dilution of elements lower than welding speed at 200 and 300 mm/min. Therefore, the hard-faced metals contained elements the most including Silicon 2.25 %, Chromium 6.12 % and Manganese 0.51 %, which affected the enhancement of mechanical properties of welded metals. The hard-faced metal had highest average hardness at 705.9 HV0.1.

Abstract: When a strip of Al-Si alloy with an Si content of 1% was cast using a vertical-type high-speed twin-roll caster, cracks form in its surface. The effects of the pouring method, the shape and position of the nozzle, and the roll surface texture on surface crack formation were evaluated with a roll caster. The rolls were made of a copper alloy, and the roll speed was 30 m/min. The as-cast strips were bent to investigate the degree of crack formation, and the outer surface of the strips was observed without magnification and with a stereomicroscope to determine the influence of the pouring method, the shape and position of the nozzle, and the roll surface. A roll machined to form V-shaped grooves 0.4 mm deep on the surface of the strips was most useful for reducing surface cracking. Changing the shape of the nozzle tip was second-most effective. There was a clear correlation between the roll surface condition and surface cracking in the Al-Si strip.

Abstract: A thin aluminum rod (width: 5 mm) was cast using a twin-wheel caster equipped with rotating side-dam plates. The upper and lower casting wheels were made of copper. The width of the flat upper and lower casting wheels was 5 mm. The rotating side-dam plate was made of mild steel. Paper 0.5 mm thick was pasted onto the plate. Boron nitride was sprayed onto the paper as an insulator and lubricant. A 6061 aluminum alloy thin rod could be cast continuously at casting speeds of 4 and 5 m/min. Molten metal was poured onto the lower wheel from a launder and conveyed into a square gap made by the lower wheel, upper wheel, and side-dam plates. The cross section of the cast rod was rectangular. The cross-sectional area of the rectangular rod was 12 to 15 mm².

Abstract: Al-4.7%Mg alloy with 0, 0.2, 0.4, 0.6 and 0.8% Fe added was cast using a copper mold and an insulator mold. The cooling rates of ingots cast using the copper mold and the insulator mold were 30.6 ^°C/s and 0.5 ^°C/s, respectively. The tensile stress and elongation of the ingots cast by the copper mold were superior to those cast by the insulator mold. The addition of Fe did not lead to tensile stress, but the elongation became smaller as the Fe content increased. The elongation of the ingot cast using the copper mold became much smaller on addition of only 0.2% Fe. The tensile stress and elongation were improved by hot forging with 50% reduction. The elongation of the ingots with Fe added was significantly improved by the hot forging. The degree of improvement of the tensile stress and elongation for the ingots cast using the insulator mold was remarkable.

Abstract: Analysis of the protection performance of kolanut leaves (KL), kolanut fruits (KF), tobacco leaves (TL) and bitter leaves (BL) extracts at 30%, 60% and 80% concentration on plain carbon steel in 0.5 M H₂SO₄ solution was done by gravimetric measurement and statistical evaluation. Data output showed KF and TL extracts performed effectively at all concentrations studied with protection performance output generally above 80%. KL and BL extracts performed poorly at the lowest concentration while at higher concentrations optimal protection performance outputs are 74.41% and 83.53%. The protection performance outputs of KL, KF and TL extracts varied significantly with observation time due to thermodynamic instability and unstable inhibition behavior. BF extract exhibited stable inhibition behavior due to general stability of its protection performance outputs with respect to observation time. BF and KL exhibited the highest and lowest standard deviation due to the degree of variation of their protection performance outputs from mean value. Data showed 9.5%, 76.2%, 76.2% and 71.4% of the protection performance outputs of KL, KF, TL and BL extracts are above 80% inhibition performance at margin of error of 12.6%, 18.2%, 18.2% and 19.3%. Data from analysis of variance shows that observation time exerted more influence than extract concentration on the protection performance outputs of KL, KF and TL extracts with statistical relevance values of 91.24%, 91.93% and 93.61%. BL extract concentration exhibited significant influence on the protection performance outputs of BL compared to observation time with statistical relevance values of 81.43%.