m. r. khanzadeh

In this research, using the manual shielded metal arc welding (SMAW) process, a wear-resistant layer was created by AMA1600v, AMA1622v, and AMA1623v hard coating electrodes on the St37 carbon mild steel, and the effect of the number of welding passes on the microstructure and corrosion resistance of the coatings was evaluated. For this purpose, optical microscope, scanning electron microscope (SEM) equipped with Energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) were used. The results showed a distribution of different carbide deposits in the microstructure of the coating metals. The deposits were complexs of the carbides of chromium, molybdenum, and vanadium. The results of the XRD demostrated the presence of martensite, austenite, chromium carbide, and molybdenum carbide phases in all three coating metals. Tungsten carbide (W2C) was observed only in the AMA1623v sample. The results of the Tafel polarization test showed that the bare and the 1622v samples had the highest corrosion current density (15.23 µA/cm2 and 7.06 µA/cm2, rspectively) among the under-studied samples, and therefore had the highest corrosion rate and the lowest corrosion resistance. Also, the results of the test showed that the corrosion current density of the 1600v sample (6.29 µA/cm2) was higher than that obtained for the 1623v sample (4.80 µA/cm2), which revealed the lower corrosion resistance of the 1600v sample. In addition, according to the results of the electrochemical impedance spectroscopy (EIS) analysis, the highest charge transfer resistance and coating resistance with the values of 6.3 kOhm.cm2 and 68.5 Ohm.cm2, respectively, belonged to the 1623v sample, which was also proven by the polarization test. Moreover, the lowest charge transfer resistance and coating resistance among the coated samples with the values of 2.73 kOhm.cm2 and 42.5 Ohm.cm2, respectively, belonged to the 1622v sample.

In this research, friction stir welding of aluminum 1050 to copper with variable speed was investigated. For friction stir welding, rotational speeds of 900 and 1200 rpm and traverse speeds of 36, 63, and 125 mm/min were used. In order to check the phases and microstructure, scanning electron microscope analysis, X-ray spectrometry, and hardness testing were used. The disturbance zone included Al2Cu3, Al4Cu9, AlCu4, Al2Cu, and AlCu phases. The results showed that the formation of intermetallic phases and severe plastic deformation in the welding area caused an increase in hardness. The highest hardness value in the stirred area was 97.8 Vickers at a rotation speed of 900 rpm and an advance speed of 36 mm/min.

The joints of dissimilar materials are widely used in industrial applications due to their technical and beneficial advantages. The dissimilar combination of aluminum and copper is generally difficult for fusion welding. This is because of formation of undesired intermetallic phases which reduces electrical conductivity in the joint interfaces. Therefore, in order to restrict these limitations solid states welding methods such as explosive welding have been suggested. Hence, in this research the effect of explosive welding parameters on microstructure, mechanical and electrical properties were investigated. Stand-off distance and thickness of explosive material were taken as the variable parameters which were affect the microstructure, mechanical and electrical properties. After conducting the Explosive welding process, Microstructural investigations using Optical and Scanning Electron Microscope which is equipped with Energy Dispersive Spectroscopy was performed. Also, for investigation of mechanical properties, hardness test was done. The results of microscopic investigations demonstrated that with increasing the thickness of explosive material, the joint interface was transformed from linear to wavy appearance. Also, the results showed that the Al-Cu interface had a higher hardness in comparison to the hardness of Al and Cu. Evaluations showed that forming the CuAl and CuAl2 intermetallic phases in the joint interface are the reason for increasing the hardness. Electrical resistance values of 0/3, 0/55, 0/38 and 0/40 mS/cm were obtained for Al-1050, Cu, Al-Cu joint interface of A and B samples.

In the current research, the microstructural changes and corrosion behavior of two-layer Steel/Bronze sheets were investigated after the heat treatment of the explosive welding process. The heat treatment was performed at 600ºC for 16 hr. Dynamic potential polarization, electrochemical impedance spectroscopy, optical microscopy, and scanning electron microscopy analyses were used. Based on of the electrochemical impedance analysis, the highest polarization resistance, which was equal to 30160 Ω cm2 and followed by the third sample having a resistance of 20720 Ω cm2, was seen in a sample with a stand-off distance of 1.5 mm and an explosive thickness of 20 mm, but the lowest polarization resistance was seen in a sample with a stand-off distance of 2 mm and an explosive thickness of 45 mm. According to the EDS analysis, from a common interface sample with a stand-off distance of 1.5 mm and an explosive thickness of 20 mm, it was concluded that the interface of steel and bronze is noble due to the high concentration of copper in the interface, therefore the corrosion speed is less than other samples. The metallographic results showed a decrease in the amplitude of the waves because of the decreasing the thickness of the explosive charge. Moreover, in the heat treatment samples, the grain size of ferrite grains has a dramatic growth, so, due to recrystallization after the heat treatment, the grains with an elongated appearance are not seen next to the interface.

Quasicrystals, unlike crystals that contain regular and repetitive patterns, are composed of regular patterns that are not repetitive. Moreover, the symmetry of quasicrystals in crystals is impossible. For example, ordinary crystals can have triple symmetries from the repetition of a triangle or quadruple symmetries from the repetition of a cube. Quasicrystals are a special type of real crystals that are artificially formed only in laboratories, under certain conditions and temperatures, and it is not possible to form them like the earth. Evidence suggests that quasicrystals can form naturally under conditions contrary to astrophysical laws and remain stable for long periods. Quasicrystals are a group of new materials with unique mechanical, physical, and chemical properties. Among the known properties of these materials are low adhesion and friction, high resistance to corrosion, very high hardness, electrical insulation at low temperatures, and light absorption. Quasicrystals are used in non-stick coatings, nanoparticles, hydrogen storage, reinforcing phases in composites, catalysts, thermal insulation, infrared light absorption, and corrosion protection. In this article, we refer to some of the main topics related to quasi-crystal