Top PDF Effect of Overageing Conditions on Microstructure and Mechanical Properties in Al–Si–Mg Alloy

American Journal of Engineering Research (AJER) e-ISSN: 2320-0847 p-ISSN : 2320-0936 Volume-5, Issue-11, pp-321-325 www.ajer.org Research Paper Open Access

Figure 2 shows the XRD patterns of solution treated (ST), CRA-20 and CRA-100 Ti-35Nb-7Zr-5Ta specimens. Only β parent phase was observed for the ST condition (Figure 2a), indicating that the alloy exhibits a martensitic start transformation (Ms) temperature lower than room temperature. This can be ascribed to the amount of β-stabilizers in the present alloy and corroborates to the fact that Zr behaves as β-stabilizer in this specific case. For the CRA-20 specimen, Figure 2b, a possible second phase formation was not evident by XRD. However, a few α and ω-precipitates start to be detectable in the CRA-100 specimen (Figure 2c), as evidenced by relative weak diffraction peaks of α(100), α(110), ω(001), ω(002) and ω(112). It is known that ω is a metastable phase that can be formed in Ti- and Zr-based alloys. The athermal ω phase precipitates after rapid quenching from single β-phase with body centered cubic (bcc) structure. On the other hand, isothermal ω structure develops after subsequent annealing at a temperature below ω solvus. After aging, isothermal ω is known to promote α phase either directly by acting as heterogeneous nucleation sites or indirectly 12,13 .

In the present study, Friction Stir Welding (FSW) of Nickel Aluminum Bronze (NAB) alloy was carried out by varying the axial load, rotation speed and welding speed rate. Micro-structural analyses of these samples revealed the different grain sizes and shapes of the various zones. Hardness and tensile strength tests were carried out for the samples welded at different conditions such as axial load, welding speed and rotational speed. Grain refinement in the weld nugget zones was achieved for all welding conditions. The refined grains in weld nugget zone (WNZ) make a main contribution to the increase of mechanical properties of FSW welded NAB alloy. The microhardness of the stir zone and Thermo-Mechanically Affected Zone (TMAZ) was found to be higher than that of the base metal. Transverse tensile strength of weld joint was higher than that of the base metal. On the other hand, a lower or similar tensile strength value compared to the base metal was seen from other variable welding parameters. This was due to the tunnel defect in the welded nugget zone. ANOVA test result was used for finding out the contribution of the process parameter.

Ceramic oxide coatings were fabricated on Ti6Al4V alloy by micro arc oxidation (MAO) in silicate electrolytes, with nano-TiO 2 and nano-Al 2 O 3 and without nano-additives. Effects of nano additives on the structural and mechanical properties of the MAO coatings were analysed. The MAO coatings were investigated by scanning electron microscopy (SEM), Energy-Dispersive spectroscopy (EDS) micro-hardness and linear wear test. Results show that the surface morphology and tribological properties of MAO coatings are greatly influenced by nano additives in electrolytes. After the coating treatment the surface hardness values increased from 300 HV 0.1 to 635 HV 0.1 . The hardness tests show that nano-Al 2 O 3 additition coating has higher microhardness values than those without any additives. The results indicated that TiO 2 and Al 2 O 3 nanoparticles into the coatings make harder and denser surface and increase the wear resistance. The wear resistance of the nano-TiO 2 and nano-Al 2 O 3 additives coatings was enhanced about 5 times than without nano additives coating.

volume fraction of β phase increased with the increase of the atomic ratio of V/Nb. The alloys were featured with lamellar microstructure with β and γ phases locating at the colony boundaries, and some β precipitates appearing at γ/γ interfaces. It was found that the colony size decreased with the increase of x. The alloys exhibited moderate mechanical properties at room temperature, with a yield strength of over 600 MPa, and fractures showed mainly translamellar character. The alloy with x=3.5 exhibited the best deformability at elevated temperature and that with x =1 had superior oxidation resistance at 800 ℃.

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T he development in light metal field is continuously pushing magnesium alloys into an important position in industrial applications for its high specific strength and specific stiffness, good castability, damping characteristic, machining and excellent electromagnetic shielding. So, more and more magnesium alloy structural components have been used in aviation, automobile and electron industries [1-4] . Due to the formation of large amount

Table 2 gives the results of mechanical tests carried out on the low-alloy cast steel with additions of vanadium and compares them with the results of previous studies made on this cast steel (designated as P1 in Tables 1 and 2) subjected to heat treatment recommended by the respective standard [9].

Braz. J. of Develop., Curitiba, v. 6, n.4,p.18681- 18696 apr. 2020. ISSN 2525-8761 study the effect of heat treatments T6 and T4 on the microstructure and mechanical properties of A356 and H1SH alloys. The alloys were casting by gravity and heat treated, with alloy A356 treated by T6 and alloy HS1H by T4 in the industrial. Initially, chemical analysis was performed to prove the chemical composition of the two alloys. The chemical composition showed that the alloy A356 contains 7.610% Si and the alloy H1SH presents 5.275% Si. The optical microscopy of the samples revealed dendritic microstructures rich in aluminum and spheroidized precipitates rich in silicon. The image analysis showed that the alloy A356 presented 86.632% of phase (α-Al), while the H1SH alloy presented 90.840%. The image analysis also showed that the alloy A356 had precipitates greater than those of the alloy H1SH. By the tensile test, it was found that the HS1H alloy presented higher values of tensile strength, however, the yield strength and elongation of the A356 alloy were higher. The Víckers microhardness demonstrated that the HS1H alloy showed greater hardness in relation to the A356 alloy.

The Laves phase reinforced CoCrMoSi alloy system has emerged as a candidate material to protect the surface of components to withstand harsh environments under wear and/or corrosion. However, previous reports have raised some concerns and restricted a wider selection of iron-based substrates to be coated, especially limiting the carbon content. This work aims to outline the Laves - Carbides phases in the microstructure and its effect on the properties of T400 alloy deposited on GGG40 ductile iron. Dilution of 26 % ensured Laves formation either as primary or secondary, due to high-silicon substrate selected. Departing from 41 % dilution, the alloy changed to a completely carbide strengthened system. Therefore, for the lowest dilution the coatings hardness is dictated by Laves phase whereas, for higher ones, carbides are the most influent phases.

Abstract: A travelling magnetic field, a power ultrasonic field, and a compound field were used separately during the horizontal continuous casting process of Al-1wt.%Si alloy. The samples obtained were characterized using an optical microscope, a scanning electron microscope, a tensile testing machine, and an electron probe microscopic analyzer to test the microstructures, properties, and element distribution of the samples. The results show that the application of a single ield can enhance the mechanical properties and reduce the segregation of Si element in Al-1wt.%Si alloy to some extent. The application of a compound field can obtain the best reinement and homogeneity of the Si element in the alloy, leading to the highest increase of tensile strength and elongation among the three applied ields. The mechanism of the action of external ields on the reinement of microstructures and homogeneity of the Si element is discussed and the compound ield is considered to be an effective method to achieve high quality Al alloys.

The presence of pinhole defect and lack of fill defect in PRE20 and PRE25 welds respectively reduce the process temperature which reduces the stir zone width in these joints [4]. The reduction in heat is because of the following; one decrease the coefficient of friction due to local melting of metal around the pin and the other is absorbed by the latent heat of melting of the metal [23]. But in the widths of thermomechanical zone and heat affected zone of these joints are increased as well as hardness reduced due to over ageing temperature and slow cool [26]. In the joint PRE20 (Fig 8b) had the pinhole defect and surrounded by partially melted metal, this is due to excess heat input to this joint. Here, the increasing in heat input did not continue in development of stir zone size due to slipping of tool. Since excess heat reduces flow stress and reduced coefficient of friction cases tool to Slip at thermomechanical zone [24]. Due to this no recrystallization take place near to pinhole defect. This microstructure image is the evidence results

4 004 Al alloy has been widely used as brazing foil in automobile, air conditioner, oxygen producer, and so on [1, 2] . In the production of 4004 Al, the high gas content results in a loose microstructure, which leads to edge cracks and strip break during the rolling process [3] . The reining of Al alloy melt is one of the key processes to improving the properties of 4004 alloy [4] . Chlorides have been widely used as reining agents in production, however the reproducibility is low and the degassing rate is affected by both the chloride types (C 2 Cl 6 , MnCl 2 , and ZnCl 2 ) and practical

The wear test was carried out under the condition of 60 N load, wear rate of 1.0 m·s -1 and wear test duration of 5 min. According to the tensile test results, the optimum Si addition amount is 1.0wt.%. Therefore, the wear test and creep test were performed on the AM60 without Si and AM60+1.0wt.%Si alloys. Figure 4 presents the variation of wear weight loss as a function of the load for the AM60 and the AM60+1.0wt.%Si alloys. It is clear that the weight loss of both AM60 and AM60+1.0wt.%Si alloys increases with increasing the load. Figure 4 also reveals that the wear weight loss of the AM60 alloy is higher than that of the AM60+1.0wt.%Si alloy. The wear weight loss of the AM60 alloy and AM60+1.0wt.%Si alloy is similar at lower loading conditions (20 N and 30 N). However, the difference in weight loss between the two alloys becomes larger at higher loads (60 N and 80 N). The transformation from micro wear to dramatic wear appears when the load is 60 N for the AM60 magnesium alloy, and the wear weight loss of the AM60 magnesium alloy at 80 N load is 2.25 times higher than that at 20 N. However, as compared to the referenced AM60 magnesium alloy, the AM60+1.0wt.%Si alloy shows considerably latter wear curve and lower weight loss especially when the load is smaller than 60 N. The wear

The aim of this work was to check the effect of the homogenization conditions on the composite powder properties as well as characteristics of the resulting ma- terials. Fig. 2 shows zeta ( ξ) potential vs. pH of the sus- pension. These plots allow us to distinguish two ranges of pH. Under acidic conditions all particles have charge of the same sign, i.e. they repel each other. At pH=9 zir- conia particles’ charge is of opposite sign than the alu- mina grains and alumina and zirconia particles should attract each other. This situation causes so called heter- oloculation effect and should improve homogenization of the system [8].

In order to further study the effect of surface alloying on the corrosion resistance, immersion tests were carried out in 3.5wt% NaCl solution, with an immersion time of 24 hours. The macro-morphologies of the corrosion specimens are shown in Fig. 8. It can be seen that the alloying samples were severely corroded. The eroded pits are present where the corrosion products peel off. On the contrary, the as-cast AZ91D was relatively less and uniformly corroded. This would suggest that the alloying layer is not contributing to the corrosion resistance of alloy, but accelerating the corrosion. This may be caused by a lack of continuity of the alloying layer on the surface, not completely covering the whole surface. On one hand, β phase is propitious to protect the matrix. But on the other hand, it would increase the corrosion rate of the alloy if the β phase and α phase form a galvanic current on account of a non-continuous distribution. So the continuity of the β phase is very important. The barrier effect only dominates the corrosion process when the β precipitates are evenly distributed. Therefore, the quality of the alloying layer can be measured in terms of microstructure whether is continuous and uniform.

Figure 3 shows that there is only α phase, no δ phase in the original sample. While in the alloy with 0.515wt.% hydrogen, lots of lath-like structures emerge (Fig. 4). By analysis of selected area of electron difraction, the lath-like structures are shown to be δ-phase hydrides. And the average width of the structures is only 0.2 μm, so it can not be seen under optical microscopy.

The metal mould had a possibility of installation of a thermocouple, which served to permanent registration, in real time, of temperature of solidifying specimen. With use of measuring station of the ATD method one registered runs of crystallization for individual specimens. Results of the registration were presented in graphic form on crystallization diagrams from the ATD method [7, 8, 9]. The tests were performed in fixed conditions. One poured specimens of the investigated alloy in the following conditions: without vibrations, with 50%ampliture of the vibrations (0,4 mm), with 100% amplitude of the vibrations (0,8 mm), frequency of vibration of 50Hz, temperature of metal mould of 250 0 C, temperature of the alloy of 760 0 C. Half of the specimens (18) were poured in horizontal position, whereas the second half of the specimens were poured in metal mould tilted with 20 0 (Fig. 3). Three pieces of specimens for each series were produced.

After 60 min of isothermal annealing the β phase formed grains with boundaries which are the most developed. With the general trend of size reduction grain β phase, with increasing time τ_ia, increase the length of the grain boundaries indicates a greater heterogeneity in size grains in the in bronze microstructure, heat treated under these conditions (Fig. 7 c). For very small grains, grains also were identified about a larger surface area and greatly developed interphase boundary. Extending the annealing time of 1β0 min possible to obtain grains of β phase with the shortest grain boundaries (Fig. 15, Tab. 7).

The above mentioned alloys were fabricated from the following starting materials (Table 1): aluminium in grade AR1 (99,96% Al), silicon of 98,5% purity (rest Fe and other elements), copper (99, 98% Cu), nickel (99, 98% Ni) and cast AG10 alloy (about 10 wt.% Mg). Melts were conducted in a Leybold-Heraeus IS5/III induction furnace with crucible of 0,7kg capacity made from magnesite refractory material. A protective coating of 2NaF and KCl was used. When the furnace temperature of ~ 820 o C had been reached, the melt was subjected to refining treatment with Rafglin-3 in an amount of 0,3 wt.%, followed by modification with Cu-P (~9,95%P). The temperature of pouring was controlled by a NiCr-NiAl TP-202K-800-1 thermocouple immersed in the bath of molten metal.