Advanced Materials – XV

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Authors: Sajawal Hussain, Muhammad Mansoor, Rehan Qayyume, Shaheed Khan
Abstract: Al-Si eutectic system is a class [Mansoor, 2014 #24] of important cast alloys accounting for the majority of aluminum parts for different industrial applications. However, in unmodified form, it attributes to the lower mechanical strength, ductility and wear characteristics. In present work, Al-9 wt. %Si alloy was prepared in unmodified and modified form, where modification was carried out using mixtures of transitional earth halides. The modification process rectified the needle like silicon rich secondary phase into acicular shape, whose effect upon the tribological characteristic of the alloy were studied using pin-on-disc method. It was found that the coefficient of friction was reduced in modified alloy, besides lowering the wear rate. The main feature of wear scar was laminates. In case of modify alloy the laminates were of uniformly formed small sized, as opposed to non-uniform predominately large sized smooth segments with cracked edges. It was postulated that these non-uniform smooth laminates were formed due to smearing resulted in high coefficient of friction and wear rate. The altered tribological characteristics were attributed to the morphology of the silicon rich secondary phase i.e. the acicular shape.
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Authors: Muhammad Mudassar Rauf, Aamir Nusair Khan, Iftichar Us Salam, Rehan Qayyume, Shaheed Khan
Abstract: A series of experiments were conducted to optimize the welding of similar and dissimilar alloys i.e AISI-321 with AISI-321, Inconel-X750 with AISI-321 and Inconel-X750 with Inconel-X750. Single phase rectification type resistance spot welding machine was utilized for this purpose. Breaking load against different welding parameters was observed. Further, the defects of the welded zone were also studied by optical and stereo microscopes. It was noted that the welding current, welding time and the welding force play an effective role in the strength of the welding joint and the spot welding of Inconel-X750 with AISI-321 can be possible if the welding parameters are carefully selected.
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Authors: Muhammad Mansoor, Muhammad Kamran Yaseen, Shaheed Khan
Abstract: Al-Si eutectic cast alloys are widely used in aeronautical and automobile industries where significantly high strength, toughness and wear resistance are required. This class of cast alloys exhibit relatively low corrosion resistance in brine environments. The mechanical properties of the alloy system mainly depend upon the shape of Si rich eutectic phase, which mainly has acicular geometry. In present research, the effect of modified microstructure of 12 wt. % Si-Al alloy on corrosion behavior was studied. The needle like Si rich eutectic phase was modified to disperse spherical structure using rare earth metal halides. The corrosion rate and pitting behavior of modified and unmodified alloy were evaluated in 3.5% NaCl solution by general corrosion for calculated time. It was observed that the corrosion rate and pitting tendency of modified alloy had been appreciably reduced as compare to unmodified alloy. The improvement of corrosion properties were the attributes of changed morphology and distribution of Si rich eutectic phase.
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Authors: Syeda Ammara Batool, Akhlaq Ahmad, Abdul Wadood, Abdul Mateen, Syed Wilayat Hussain
Abstract: Aluminum (Al) and Titanium (Ti) based lightweight alloys have been a topic of discussion and research for a few decades now. Resulting alloys with hard intermetallic phases in Al-Ti binary system have good microstructural and mechanical properties including low densities, high specific strength, better resistance against oxidation and corrosion which are highly desirable in aerospace industry. Such an alloy system was studied in our research. Powder metallurgy (PM) was used as processing route because of its economical and easy operation. Samples were prepared using metallic powders of Aluminum (Al) and Titanium (Ti) with varying compositions of 95 at.% Al-Ti, 90 at.% Al-Ti and 88 at.% Al-10 at.% Ti-2 at.% SiC. After compaction, pressureless sintering was carried out at 620°C for several hours in Argon atmosphere followed by annealing resulting in a reasonably dense Al-Ti alloy. Microstructure and phase composition of alloy was analyzed by Scanning electron microscopy (SEM) and Energy dispersive spectroscopy (EDS), respectively. Hardness was evaluated by Vickers micro indentation test. An increase in hardness was observed. Sample containing reinforcement particles (SiC) demonstrated highest value of hardness.
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Authors: Muhammad Shahzad, Tanveer Manzoor, Qanita Tayyaba, Ammad Hussain Qureshi
Abstract: Presented results report the findings of a case study carried out to determine the possible factors that lead to the twisting of tail rotor shaft. The structural materials of the shaft was evaluated in terms of microstructural analysis and mechanical properties to rule out any material fault. The SEM images showed that the localized fractures at twist ends occurred without any significant plastic deformation. Moreover, there was no evidence of fatigue. Such behavior suggests that twist occurred under impact / high strain rate loading. Such loading conditions are not possible during the event to ground hitting. The Ansys simulation confirmed that the observed twisting can increase the stress at localized point in excess of UTS and cause fracture.
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Authors: Javed Kamran, Hasan bin Awais, Naeem Ul Haq Tariq, Yin Wang
Abstract: In the present investigation the rolling response, microstructure and texture evolution of four Mg alloys during multi-pass warm rolling were evaluated. The nominal composition of the base alloy (alloy-1) was Mg-3Al-1Zn. The alloy-2, 3 and 4 were developed by separate additions of non-rare earth elements Ag and In, and a master alloy 85Ag15In (wt.%) to make target compositions Mg-3Al-1Zn-0.5x, (x = Ag ,In, AgIn). Samples from all four alloys were subjected to multi-pass warm rolling at 300 °C to accumulative reductions of 50, 75 and 90% with 8 minutes inter-pass annealing. For all four alloys, crack free sheets of less than 1 mm thickness were produced successfully with true strain corresponding to 90% reduction. The as-cast microstructures revealed second phase particles at grain boundaries and grains interiors for all alloys. A slight scatter in the size of the deformed grains was observed for alloy-1, 2 and 3 after rolling reductions of 50, 75 and 90%. However, a sustained decrease in grain size with increasing the rolling reductions was only observed in alloy-4, despite inter-pass annealing. XRD macro-texture results of alloy-2 and 3 presented very strong basal texture showing almost concentric contours around normal direction (ND). Such strong sheet texture is attributed to a preferential alignment of basal planes parallel to the sheet surface. On the other hand alloy-1 and alloy-4 revealed a weaker texture with basal poles spread more towards transverse direction (TD) as compared to rolling direction (RD) and may be due to the activation of some <c+a> non-basal slip and twinning in addition to basal slip under the same processing parameters.
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Authors: Tayyaba Zaman, Rehan Qayyume, Amjad Ali, Shaheed Khan, Chaoli Maa
Abstract: Deformation response of Al-4.46Mg-0.48Mn alloy under uniaxial tensile loading was investigated at temperatures ranging from 400°C - 525°C and at strain rates of 3x10-3 s-1, 1x 10-3 s-1 & 10-4 s-1. The alloy exhibited a maximum elongation >480% at a strain rate of 10-3s-1 and 525°C. At all conditions, the dominant deformation mechanism governing the superplastic deformation was investigated as a function of strain rate and temperature. The contributions of strain-rate sensitivity and strain hardening were analyzed in relation to the observed tensile ductility. The strain rate sensitivity index (m) and average activation energy (Q) values revealed that the dominant deformation mechanism is grain boundary sliding (GBS). The GBS phenomenon was further confirmed through high magnification examination of deformed surface. Optical microscopy (OM) and Scanning Electron Microscopy (SEM) showed that dynamic re-crystallization occurs during hot deformation of the alloy which causes reasonable enhancement of plasticity.
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Authors: Naveed Akhtar, Muhammad Afzal, Muhammad Awais, Muhammad Akbar
Abstract: Quenching residual stresses in Al-Mg-Si alloy forged disc were balanced via cold deformation compression method. In this experiment firstly, the forged disc of Φ210x52 mm was prepared from extruded stock material of Φ160x90 mm through close die forging technique. Next, the forged discs were quenched in water and cold compressed immediately. Finally, the discs were artificial aged to finish in T652 temper. Close die forging and cold compression deformation was performed on a 1200 Ton hydraulic forging press. The amount of cold compression deformation was varied from 2.0 to 5.0% to gauge the optimum level of cold compression for the removal of quenching residual stresses. The residual stresses were measured in terms of dimensional stability of the machined component. Results showed that the 3.8% cold compression deformation was the optimized value for the work piece geometry under investigation. Further, the effect of cold (room temperature) and hot water (~60°C) quenching on the residual stresses was also studied and compared with that of cold compression method.
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Authors: Muhammad Kamran Yaseen, Muhammad Mansoor, Haider Ali Ansari, Sajawal Hussain, Shaheed Khan
Abstract: Al bronze are the choice of material for relatively high wear applications besides appreciable mechanical and corrosion properties. In present work, the effect of different heat treatment processes on tribological characteristics of Ni-Al bronze (CuAl10Ni5Fe4, UNS C63000) has been studied. The hot rolled bar of 30 mm diameter was subjected to annealing, quenching and aging processes separately, consequently their effect on microstructure was studied and co-related with tribological characteristics. The formation and nucleation of various phases due to the thermal treatments were observed using optical microscopy. The wear behavior was studied using ball on disk arrangement with 100Cr6 ball and Ni-Al Bronze samples as disk. The characteristics and mechanism of wear track was studied using scanning electron microscope. It was observed that the water quenched sample followed by aging at 300°C exhibited best tribological characteristics.
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