Volume 55, Issue 6

In this study, one of the solid state welding methods, friction stir welding, was studied with the AA6082 aluminum alloy. Two types of pins with a special geometry were used to investigate the effect of pins profile, tool rotational speed, and welding speed on the mechanical properties of welded joints. The pin profile was associated with weld joint properties such as tensile strength, elongation, bending strength, bending force, hardness distributions and temperature. Results have shown that the friction surface area of the pin has a significant role on the mechanical behaviour of the joint. The results of tensile tests associated with the pin profile indicate that the helical two-flute pin has a high tensile strength and elongation compared to the helical four-flute pin. Discrepancies in the tensile strength of the welded samples of the two pin profiles have been found between 37–55 % at the same welding conditions. Despite the relatively poor static properties, the helical four-flute pin has better bending properties. Higher bending strength and force (260.634 MPa and 347.513 daN) were obtained at test conditions of 2000 rpm and 100 mm/min. Bending without any defect on the joint was achieved at 2000 rpm and 200 mm/min. The effect of welding parameters on the hardness profile was not clear, and it has been observed that, in comparison, the helical two-flute pin did not create a remarkable difference with regard to hardness.

Materials difficult to weld by fusion welding processes can be successfully welded by friction welding. The strength of the friction welded joints is extremely affected by process parameters (rotation speed, friction time, friction pressure, forging time, and forging pressure). In this study, statistical values of tensile strength were investigated in terms of rotation speed, friction time, and friction pressure on the strength behaviours of friction welded AISI 1040 and AISI 304L alloys. Then, the tensile test results were analyzed by analysis of variance (ANOVA) with a confidence level of 95 % to find out whether a statistically significant difference occurs. As a result of this study, the maximum tensile strength is very close, which that of AISI 1040 parent metal of 637 MPa to could be obtained for the joints fabricated under the welding conditions of rotation speed of 1700 rpm, friction pressure of 50 MPa, forging pressure of 100 MPa, friction time of 4 s, and forging time of 2 s. Rotation speed, friction time, and friction pressure on the friction welding of AISI 1040 and AISI 304L alloys were statistically significant regarding tensile strength test values.

Friction welding is a solid-state welding method, which can join different materials smoothly and is excessively used in manufacturing industry. Friction welding method is commonly used in welding applications of especially cylindrical components, pipes and materials with different properties, for which other welding methods remain incapable. AISI 304 stainless steel and a copper alloy of 99.6 % purity were used in this study. This couple was welded in the friction welding machine. After the welding process, samples were analyzed macroscopically and microscopically, and their microhardness was measured. Tensile test was used to determine the bond strength of materials that were joined using the friction welding method. At the end of the study, it was observed that AISI 304 stainless steel and copper could be welded smoothly using the friction welding method and the bond strength is close to the tensile strength of copper.

Duplex stainless steels have wide applications in industry due to their high mechanical strength, excellent toughness, and high corrosion resistance regarding to other types of steels. However, these steels are susceptible to form brittle phases during heat treatment associated to manufacture or welding processes, in particular the negative effect of sigma-phase into ferrite-austenitic microstructure has to be pointed out. In this work, a study is carried out about the use of ultrasonic nondestructive technique to establish a relationship between sigma phase signal percentages in 2507 duplex stainless steel and more relevant features of the collected ultrasonic signal in an equation. Thus, a novel method is obtained to perform the inspection of these materials in-situ in order to avoid the loss of mechanical resistance and to increase the susceptibility to localized corrosion in service.

In the present investigation, the effects of plasma nitriding pressure and time on the structural and tribological characterization of AISI D6 grade cold work tool steel were studied. DC glow discharge plasma nitriding process under NH 3 gas was performed at temperatures of 500 °C and at pressures of 150 Pa, 450 Pa and 800 Pa for durations of 2 h, 7 h and 10 h. The mass loss and the coefficient of friction were measured using a ball-on-disc wear test with 1.668 N, 4.143 N, and 9.113 N test loads. Cross-section and surface characterizations were evaluated using optical microscopy, SEM, and microhardness test techniques. The surface microhardness was found to increase with the nitriding time and the pressure. The wear resistance of the specimen strongly depends on the nitriding parameters and the applied test load in determining whether a plastic deformation of the surface layer has occurred or not.

In this study, the optimization of the abrasive wear behaviour of a medium carbon steel surface with a FeCrC/B 4 C powder coating applied by using the plasma arc weld surfacing process is examined. Optimization of the process parameters represents the key step in the Taguchi method to achieve high quality without increasing cost. The Taguchi method uses orthogonal arrays to maximize the effect of controllable parameters and to minimize the effect of uncontrollable process para­meters. The abrasive wear behaviour of the surface of a medium carbon steel substrate material coated with FeCrC and with 15 % or 25 % B 4 C was tested at loads of 10 N, 20 N, and 30 N and at distances of 10 m, 20 m, and 30 m. The lowest wear loss, representing the most important criterion in determining the wear behaviour, was optimized with the so-called lowest-the best control characteristics of the Taguchi method and the results were analyzed by graphical methods.

In this study, the sliding wear behaviour of non-aged and aged Cu-Cr-Zr alloy specimens were investigated. The specimens were aged for 2 h at the temperatures of 450 °C and 475 °C. Prior to the wear tests, microstructural examinations and hardness measurements were performed on all Cu-Cr-Zr alloy specimens. The wear tests were performed on a pin-on disk type wear apparatus at the sliding speeds of 0.5 ms −1 , 1.0 ms −1 and 1.5 ms −1 as well as under 40 N applied load. After the wear tests, the worn surfaces of all samples were analyzed by SEM and energy dispersive X-ray spectroscopy (EDS). The experimental results indicated that aging heat treatment led to increase in the hardness values of Cu-Cr-Zr alloys and the highest wear loss was observed for non-aged specimens. With increasing sliding speed, the wear loss increased to a maximum value beyond which it decreased.

The suitable selection of manufacturing process and conditions are very important in manufacturing processes to obtain good surface quality and dimensional precision. Thus, it is required to know properties relating to material, surface quality and dimensional precision by means of mathematical models which allow some predictions taking into account operation conditions such as feed rate, current and pulse on time, etc. Wire electrical discharge machining (WEDM) represents a modification of electro discharge machining (EDM) and is widely used for a long time for cutting punches and dies, shaped pockets as well as other machine parts on conductive work materials. Present work is focused on the regression modeling predicting diameter and circularity deviation of a hot work tool steel. Mathematical relationships between circularity and diameter deviation as well as WEDM cutting parameters (feed rate, current and pulse on time) have been investigated. Results show that, regression analysis can be successfully applied for this mathematical model.

The change in width of sea ice cracks seriously affects the transportation during human's activities in the Antarctic sea, but there are few automatic technologies for accurate monitoring of such cracks. To solve this problem, an automatic detecting apparatus for sea ice cracks was designed, and its feasibility and monitoring principles were studied. Furthermore, a practical methodology was developed and such apparatus was applied to the testing of the Antarctic sea ice cracks. The testing results showed that the data were reliable and stable for the analysis of icing behaviour.

ISO 10113:2006 standard includes determination of plastic anisotropy (r-value). The r-value is one of the indices of the ductility of cold-rolled steel sheets. The article compares manual and automatic mathematical methods and their results.

This study was carried out to investigate the relationship between the strain and acoustic emission (AE) signals to ascertain the applicability of AE in predicting the fatigue life of metallic specimens. This paper is an extension research of previous work that has been published before. Previous paper presents the ability of AE to predict the fatigue life using statistical parameters such as root mean square (r.m.s) and kurtosis. The same approach also has been carried out in this recent paper but this time, the common parameters that can be directly extracted from the AE data acquisition system were used. To achieve the objective, the strain and AE signals were measured using a strain gauge and a AE piezoelectric transducer on SAE 1045 steel specimens. These measurements were conducted during the cyclic test at constant loadings of 570 MPa, 610 MPa, and 650 MPa. For data collection, AE parameters, i. e., count rate, hits, and duration, were extracted from specific software and were then correlated to fatigue lives calculated using the strain data. Fatigue life values were calculated using strain-life models. The correlation between the experimental and predicted values of fatigue life was then established by the so-called coefficient of correlation which is within 97.2 % and 98.5 % for the Coffin-Manson model and between 92.7 % and 94.3 % for the Smith-Watson-Topper model, respectively. As for the Morrow model, the coefficient of correlation was tabulated at approximately between 71.9 % and 73.6 %. Good correlation values expressed that the AE technique is applicable for predicting the fatigue life of metallic specimens.