ABSTRACT
In this study, the microstructural properties, wear resistance, and corrosion behavior of H111 hot-rolled AA5754 alloy before heat treatment, after homogenization, and after aging were examined. The microstructure was mainly composed of the scattered forms of black and gray contrast particles on the matrix and precipitations were observed at the boundaries of the grain. The as-rolled material exhibited a dense pancake-shaped grain structure, which is typical of as-rolled material. Observation along the L-direction did not yield distinct demarcations among the grains and was not uniformly distributed, with precipitates at the grain boundary. When they aged, there was a parallel increase in fine and huge black and gray contrast particles in the zone. Therefore, it could be stated that the amount of fine grains increased due to the rise in the homogenization process. The rolled base metal with the grain orientation was found to be parallel to the rolling direction. On the other hand, the coarse grains were clearly observed in the aging heat-treatment condition. The grains had an elongated morphology consistent with the rolling process of the metal before the heat-treatment process. The aged alloy had the highest hardness with a value of 86.83 HB; the lowest hardness was seen in the alloy before heat treatment with a value of 68.67 HB. The weight loss and wear rate of this material at the end of 10,000 m were, respectively, 1.01 × 10-3 g and 5.07 × 10-9 g/Nm. It was observed that the alloy had the highest weight loss and worst wear resistance before heat treatment. Weight loss and wear rates at the end of 10,000 m were, respectively, 3.42 × 10-3 g and 17.08 × 10-9 g/Nm. According to these results, the friction coefficients during wear were parallel and the material with the lowest friction coefficient after aging was 0.045. While the alloys corroded after aging showed more weight loss, the alloys corroded before heat treatment exhibited better corrosion behavior. Among the alloys, the least weight loss after 24 h was observed in the alloy that was corroded before heat treatment and this value was 0.69 × 10-3 mg/dm2. The highest weight loss was observed in the aged alloy with a value of 1.37 × 10-3 mg/dm2. The alloy before heat treatment, which corroded after casting, showed the lowest corrosion rate with a value of 0.39 × 10-3 mg/(dm2·day) after 72 h. The alloy that was corroded before heat treatment showed the best corrosion behavior by creating a corrosion potential of 1.04 ± 1.5 V at a current density of -586 ± 0.04 µA/cm2. However, after aging, the corroded alloy showed the worst corrosion behavior with a corrosion potential of 5.16 ± 3.3 V at a current density of -880 ± 0.01 µA/cm2.
ABSTRACT
In this study, an Al5083-H111 alloy was divided into two different parameters without heat treatment and by applying homogenization heat treatment. In the homogenized Al5083 sample, it helped to make the matrix structure more homogeneous and refined and distribute intermetallic phases, such as the Al-Mg phase (Mg2Al3) and Al-Fe phases, more evenly in the matrix. There was an increase in the hardness of the homogenized sample. The increase in hardness is due to the material having a more homogeneous structure. Corrosion tests were applied to these parameters in NaCl and NaOH. It is observed that Al5083 samples before and after heat treatment show better corrosion resistance and less weight loss in NaOH and NaCl environments. It was observed that the fracture resistance of the alloy in the NaOH solution was lower, and the weight loss was higher than the alloy in the NaCl solution. Wear tests were performed on two different parameters: a dry environment and a NaOH solution. Since the NaOH solution has a lubricating effect on the wear surface of the sample and increases the corrosion resistance of the oxide layers formed, the wear resistance of the alloys in dry environments was lower than the wear resistance of the alloys in the NaOH solution. A hydrogen evolution test was performed on the samples in the NaOH solution, and the results were recorded. Hydrogen production showed higher hydrogen output from the homogenized sample. Accordingly, a higher corrosion rate was observed.
ABSTRACT
In this study, microstructural characterization, mechanical (tensile and compressive) properties, and tribological (wear) properties of Titanium Grade 5 alloy after the oxidation process were examined. While it is observed that the grey contrast coloured α grains are coaxial in the microstructures, it is seen that there are black contrast coloured ß grains at the grain boundaries. However, in oxidised Titanium Grade 5, it is possible to observe that the α structure becomes larger, and the number and density of the structure increases. Small-sized structures can be seen inside the growing α particles and on the ß particles. These structures are predicted to be Al-Ti/Al-V secondary phases. The nonoxidised alloy matrix and the OL layer exhibited a macrolevel hardness of 335 ± 3.21 HB and 353 ± 1.62 HB, respectively. The heat treatment increased Vickers microhardness by 13% in polished and etched nonoxidised and oxidised alloys, from 309 ± 2.08 HV1 to 352 ± 1.43 HV1. The Vickers microhardness value of the oxidised sample was 528 ± 1.74 HV1, as a 50% increase was noted. According to their tensile properties, oxidised alloys showed a better result compared to nonoxidised alloys. While the peak stress in the oxidised alloy was 1028.40 MPa, in the nonoxidised alloy, this value was 1027.20 MPa. It is seen that the peak stresses of both materials are close to each other, and the result of the oxidised alloy is slightly better. When we look at the breaking strain to characterise the deformation behaviour in the materials, it is 0.084 mm/mm in the oxidised alloy; In the nonoxidised alloy, it is 0.066 mm/mm. When we look at the stress at offset yield of the two alloys, it is 694.56 MPa in the oxidised alloy; it was found to be 674.092 MPa in the nonoxidised alloy. According to their compressive test properties, the maximum compressive strength is 2164.32 MPa in the oxidised alloy; in the nonoxidised alloy, it is 1531.52 MPa. While the yield strength is 972.50 MPa in oxidised Titanium Grade 5, it was found to be 934.16 MPa in nonoxidised Titanium Grade 5. When the compressive deformation oxidised alloy is 100.01%, in the nonoxidised alloy, it is 68.50%. According to their tribological properties, the oxidised alloy provided the least weight loss after 10,000 m and had the best wear resistance. This material's weight loss and wear coefficient at the end of 10,000 m are 0.127 ± 0.0002 g and (63.45 ± 0.15) × 10-8 g/Nm, respectively. The highest weight loss and worst wear resistance have been observed in the nonoxidised alloy. The weight loss and wear coefficients at the end of 10,000 m are 0.140 ± 0.0003 g and (69.75 ± 0.09) × 10-8 g/Nm, respectively. The oxidation process has been shown to improve the tribological properties of Titanium Grade 5 alloy.
ABSTRACT
This study deals with the microstructure of rolled Al5083-H111 materials, their hardness, corrosion in different solutions, and rotary bending fatigue properties of non-corroded and corroded samples in different solutions. This study is the first to report the fatigue behavior of corroded samples in different aggressive corrosion environments of Al5083. The microstructure of the Al5083-H111 material is in the form of grains oriented towards the rolling direction and it consists of binary Al-Mg, Al-Mn, and Mg-Si; ternary Al-Mg-Si; and quaternary Al-Mn-Fe-Si and Al-Cr-Mn precipitated randomly at the grain boundary. The Brinell hardness of the Al5083-H111 material is 68.67 HB. According to the results of the immersion corrosion, while the sample was more resistant to corrosion in a 3.5% NaCl environment, it showed a less resistant behavior in a 3.5% NaCl + 10% HCl environment. As a result of the fatigue test, it was observed that the sample that did not undergo corrosion showed a higher fatigue life than the samples that were exposed to corrosion. The fatigue rate of the 3.5% NaCl corrosion sample was 3.5 times lower than the fatigue rate of the 3.5% NaCl + 10% HCl corrosion sample.
ABSTRACT
In this study, the microstructural properties and corrosion behavior of RE elements (Y, La) added to magnesium in varying minors after casting and homogenization heat treatment were investigated. Three-phase structures, such as α-Mg, lamellae-like phases, and network-shaped eutectic compounds, were seen in the microstructure results. The dendrite-like phases were evenly distributed from the eutectic compounds to the interior of the α-Mg grains, while the eutectic compounds (α-Mg + Mg) RE (La/Y)) were distributed at the grain boundaries. According to the corrosion results, the typical hydroxide formation for lanthanum content caused the formation of crater structures in the material, and with the increase in lanthanum content, these crater structures increased both in depth and in density. In addition, the corrosion products formed by Y2O3 and Y(OH)3 in the Mg-3.21Y-3.15 La alloy increased the thickness of the corrosion film and formed a barrier that protects the material against corrosion. The thinness of the protective barrier against corrosion in the Mg-4.71 Y-3.98 La alloy is due to the increased lanthanum and yttrium ratios. In addition, the corrosion resistance of both Mg-3.21Y-3.15 La and Mg-4.71 Y-3.98 La alloys decreases after homogenization. This negative effect on corrosion is due to the coaxial distribution of oxide/hydroxide layers formed by yttrium and lanthanum after homogenization.
ABSTRACT
In this study, corrosion and wear tests of NiTi alloy (Ni 55%-Ti 45%) samples, known as shape memory alloy, which offer a shape recovery memory effect between memory temperatures ranging from 25 to 35 °C, have been carried out. The standard metallographically prepared samples' microstructure images were obtained using an optical microscope device and SEM with an EDS analyzer. For the corrosion test, the samples are immersed with a net into the beaker of synthetic body fluid, whose contact with the standard air is cut off. Electrochemical corrosion analyses were performed after potentiodynamic testing in synthetic body fluid and at room temperature. The wear tests of the investigated NiTi superalloy were carried out by performing reciprocal wear tests under 20 N and 40 N loads in a dry environment and body fluid. During wear, a 100CR6-quality steel ball of the counter material was rubbed on the sample surface for a total of 300 m with a unit line length of 13 mm and a sliding speed of 0.04 m/s. As a result of both the potentiodynamic polarization and immersion corrosion tests in the body fluid, an average of 50% thickness reduction in the samples was observed in proportion to the change in the corrosion current values. In addition, the weight loss of the samples in corrosive wear is 20% less than that in dry wear. This can be attributed to the protective effect of the oxide film on the surface at high loads and the effect of reducing the friction coefficient of the body fluid.
ABSTRACT
In this study, Al7075+0%Ti-, Al7075+2%Ti-, Al7075+4%Ti-, and Al7075+8%Ti-reinforced alloys were prepared by melting processes using Al7075 and Al-10%Ti main alloys. All newly produced alloys were subjected to T6 aging heat treatment and some samples were cold rolled at 5% beforehand. The microstructure, mechanical behavior, and dry-wear behavior of the new alloys were examined. Dry-wear tests of all alloys were carried out at a total sliding distance of 1000 m, at a sliding speed of 0.1 m/s, and under a load of 20 N. In the hardness measured after T6 aging heat treatment, the peak hardness of the Al7075+0%Ti-, Al7075+2%Ti-, Al7075+4%Ti-, and Al7075+8%Ti-reinforced alloys was found to be 105.63, 113.60, 122.44, and 140.41 HB, respectively. The secondary phases formed by the addition of Ti to the Al7075 alloy acted as precipitate-nucleation sites during aging heat treatment, further increasing the peak hardness. Compared to the peak hardness of the unrolled Al7075+0%Ti alloy, the increase in the peak hardness of the unrolled and rolled Al7075+8%Ti-reinforced alloys was 34% and 47%, respectively, and this difference in the increase was due to the change in the dislocation density with cold deformation. According to the dry-wear test results, the wear resistance of the Al7075 alloy increased by 108.5% with a reinforcement of 8% Ti. This result can be attributed to the formation of Al, Mg, and Ti-based oxide films during wear, as well as the precipitation hardening, the secondary hardening with acicular and spherical Al3Ti phases, the grain refinement, and solid-solution-hardening mechanisms.
ABSTRACT
This study deals with the microstructure, mechanical, and wear properties of the extruded ZK60 matrix composites strengthened with 45 µm, 15% silicon carbide particle (SiC) and 760 nm, 0.2-0.5% aluminium nitride (AlN) nanoparticle reinforcements. First, the reinforcement elements of the composites, SiC and AlN mixtures were prepared in master-magnesium powder, and compacts were formed under 450 MPa pressure and then sintered. Second, the compacted reinforcing elements were placed into the ZK60 alloy matrix at the semi-solid melt temperature, and the melt was mixed by mechanical mixing. After the melts were mixed for 30 min and a homogeneous mixture was formed, the mixtures were poured into metal moulds and composite samples were obtained. After being homogenized for 24 h at 400 °C, the alloys were extruded with a 16:1 deformation ratio at 310 °C and a ram speed of 0.3 mm/s to create final composite samples. After microstructure characterization and hardness analysis, the dry friction behavior of all composite samples was investigated. Depending on the percentage ratios of SIC and AlN reinforcement elements in the matrix, it was seen that the compressive strength and hardness of the composites increased, and the friction coefficient decreased. While the wear rate of the unreinforced ZK60 alloy was 3.89 × 10-5 g/m, this value decreased by 26.2 percent to 2.87 × 10-5 g/m in the 0.5% AlN + 15% SiC reinforced ZK 60 alloy.
