Assessment of the Corrosion Behavior of Friction-Stir-Welded Dissimilar Aluminum Alloys

The fuel consumption of high-density automobiles has increased in recent years. Aluminum (Al) alloy is a suitable material for weight reduction in vehicles with high ductility and low weight. To address environmental problems in aircraft and maritime applications, in particular rust development and corrosion, the current study assesses the corrosion behavior during friction stir welding (FSW) of two dissimilar Al alloys (AA6061 and AA8011) in various corrosive conditions using salt spraying and submersion tests. Two acidic solutions and one alkaline solution are used in these tests, which are performed at room temperature. The two specimens (AA6061 and AA8011) and the weld region are suspended in a salt spraying chamber and a 5 wt.% NaCl solution is continually sprayed using the circulation pump for 60 h, with the specimens being weighed every 15 h to determine the corrosion rates. According to the salt spraying data, the weld zone has a higher corrosion resistance than the core components. For twenty-eight days, individual specimens are submerged in 3.5 wt.% HCl + H2O and H2SO4 + H2O solutions and seawater. The weld area specimens exhibit stronger corrosion resistance than the base material specimens, and weight loss in the saltwater medium is lower when compared to the other test solutions, according to the corrosion analysis. The scanning electron microscope (SEM) analysis demonstrates that the base metal AA8011 is considerably corroded on its surface.

The Effect of a Hollow Fixture on Energy Dissipation of Ultrasonic Welded Carbon Fiber/Polyamide 66 Composite

In this study, the effect of the fixture configuration on ultrasonic welding of 4-mm-thick carbon-fiber-reinforced polyamide 66 (CF/PA66) composite with 30% mass fiber was evaluated. An analytical model to estimate the energy dissipation in the welding zone of lapped CF/PA66 samples was derived. Calculation analyses showed the energy dissipation at the faying interface of joints made from hollow-fixture ultrasonic welding (HFUSW) was about 25% higher than those made from conventional ultrasonic welding (CUSW) under the given process variables. This was primarily attributed to the almost total reflection at the workpiece-to-fixture interface in HFUSW. Experimental results indicated that the HFUSW joints exhibited a greater peak load and weld area than CUSW joints when the weld time was less than 2.1 s. The optimal weld time for CUSW and HFUSW processes were 2.1 and 1.7 s. When the weld time exceeded the optimal time, the joints occurred with a porous region, which was caused by thermal decomposition of the material, resulting in the decrease in peak load. Experimental and simulation results demonstrated the HFUSW process changed the propagation behavior of the ultrasonic wave and enhanced the energy dissipation at the faying interface. This study enriched the understanding of energy dissipation during ultrasonic welding of polymers.

Analisis Kekerasan Hasil Pengelasan Gas Tungsten Arc Welding pada Baja ST 37 dengan Variasi Media Pendingin

Cooling media is a substance that increases the hardness value of a materialthrough a heat-treatment process. This study aims to determine the effect of cooling media on the hardness of ST 37 steel due to Gas Tungsten Arc Welding (GTAW). The method used is an experimental method using the independent variables, namely water cooling media, seawater cooling media, and oil cooling media, while the dependent variable is the hardness test result. In specimens using water cooling media, the hardness in the weld area is 47.19 kg/mm2, in the HAZ area the it is 54.6 kg/mm2, and the base metal gets a value of 40.87 kg/mm2. While the specimens with seawater cooling media get a value in the weld area of 76.37 kg/mm2, in the HAZ area it gets a value of 83.89 kg/mm2 and the base metal gets a value of 70.13 kg/mm2. The specimens with oil cooling media the value in the weld area is 40.77 kg/mm2, in the HAZ area it gets a value of 43.32 kg/mm2 and the base metal gets a value of 36.09 kg/mm2 . From the hardness values obtained, specimens immersed in seawater cooling media have the highest hardness values compared to water and oil cooling media.

Simulation Analysis of Thermal Mixing Characteristics of Fluids Flowing Through a Converging T-junction

Temperature fluctuation occurs while mixing of hot and cold fluids in a T-junction due to incomplete thermal mixing. This temperature fluctuation can produce thermal fatigue at the weld area of the T-junction. The present study aims to numerically investigate the thermal mixing characteristics of hot and cold fluids in a T-junction. The realizable k-ε turbulence model is used with natural gas as the working fluid. Temperature distribution, mixing quality, and intensity of temperature fluctuation are evaluated and compared along with the mixing outlet. The inlet temperature difference and branch to main pipe flowrate ratio have a direct influence on thermal mixing. The higher temperature difference can reduce the thermal mixing performance. Thermal mixing increases with the increase of branch to main pipe flowrate. The intensity of temperature fluctuation is found within a short distance from the intersecting point of the two inlets. With the increase of distance along with the mixing outlet, the frequency of temperature fluctuation decreases, and thermal mixing increases.

The Study of Corrosion Behaviors of Carbon Steel Weldments and Their Inhibition in Simulated Pore Solution Using Multi-Electrode Array Technique

A multi-electrode array sensor was developed to study the corrosion behaviors of carbon steel weldments and the effectiveness of the NaNO2 inhibitor in carbonated pore solution. The sensor can simulate a complete weldment, and the measurement results can match well with the coupon immersion test. The galvanic corrosion between the weld area, heat-affected area, and base metal area, as well as the effect of nitrite corrosion inhibitor on the weld area, were observed by measuring the open circuit potential, coupling potential, and galvanic current. The results show that corrosion is likely to happen around the weld metal area and its adjacent heat-affected zone. The intensive galvanic currents can accelerate the localized corrosion, while NaNO2 can inhibit it.

Weld defect inspection based on machine vision and weak magnetic technology

This study proposes a weld defect inspection method based on a combination of machine vision and weak magnetic technology to inspect the quality of weld formation comprehensively. In accordance with the principle of laser triangulation, surface information about the weldment is obtained, the weld area is extracted using mutation characteristics of the weld edge and an algorithm for identifying defects with abnormal average height in the weld surface is proposed. Subsequently, a welding seam inspection process is developed and implemented, which is composed of a camera, a structured light sensor, a magnetic sensor and a motion control system. Inspection results from an austenitic stainless steel weldment show that the method combining machine vision and magnetism can identify defect locations accurately. Comprehensive analysis of the test results can effectively classify surface and internal defects, estimate the equivalent sizes of defects and evaluate the quality of weld formation in multiple dimensions.

Experimental Study on Welding Process of TC4 Titanium Alloy with Different Welding Wires

In present study, the effects of different welding wires on the evolution of microstructure and mechanical properties of TC4 titanium alloy test plates were studied. The results show that the test plates welded by TA20 titanium alloy wire, TC3 titanium alloy wire and TC4 titanium alloy wire are well formed, no defects are found in the cross section of the weld. The microstructures of these test plates are similar, and needle-like martensite exists in the weld area. In comparison, this is little obvious difference in tensile strength among these test plates welded by different welding wires, while the plates welded by TC4 titanium alloy has better elongation, contraction of aera, impact toughness and better balance of strength and toughness.

Evaluation of Cracks on the Welding of Austenitic Stainless Steel Using Experimental and Numerical Techniques

This paper deals with investigation and characterization of weld circumferential thin cracks in austenitic stainless steel (AISI 304) pipe with eddy current nondestructive testing technique (EC-NDT). During welding process, the heat source applied to the AISI 304 was not uniform, accompanied by a change of the physical property. To take into consideration this change, the relative magnetic permeability was considered as a gradiently changed variable in the weld and the heat affected zone (HAZ), which was generated by the Monte Carlo Method based on pseudo random number generation (PRNG). Numerical simulations were performed by means of MATLAB software using 2D finite element method to solve the problem. To verify, results from the modeling works were conducted and contrasted with findings from experimental ones. Indeed, the results of comparison agreed well. In addition, they show that considering this changing of this magnetic property allows distinguishing the thin cracks in the weld area.

THE EFFECT OF WELDING CURRENT ON AISI 1045 STRENGTH AND CORROSION RATE

Shielded Metal Arc Welding (SMAW) was widely used in industry for joining AISI 1045 steel because this method was simple, in-expensive, and the device is portable. This researched aimed to analyze the effect of variations in welding current towards material strength and corrosion rate of AISI 1045. Welding current that been used as variations in this study are 100, 110, and 120 Ampere. This research was conducted using tensile test on the weld area and immersion around the weld area in NaCl solution with 0.4% concentration. From the research that conducted, it is known that increasing in welding current made the yield strength, tensile strength, and fracture strength of material also increased. This phenomenon also happened for elongation of material in weld area. With increasing the welding current then the elongation of material also increasing. Another aspect that researched in this paper is the effect of welding current toward corrosion rate of material. From the result, it was known that increasing welding current made corrosion rate of material became faster.

Load Controlled Fatigue Behaviour of Microplasma Arc Welded Thin Titanium Grade 5 (6Al-4V) Sheets

The current study investigates the load controlled fatigue properties of the microplasma arc welded thin titanium Grade 5 (6Al-4V) sheets. In order to explore the effect of weld geometry on the fatigue, two different welded joints were used in the experimental studies. Load controlled fatigue test results were evaluated to present an outlook on the behaviour of microplasma welded titanium alloy Grade 5 sheets under cyclic loading. Even though the previously published monotonic tests showed successful use of microplasma arc welding to join thin titanium Grade 5 sheets with mechanical properties comparable to the base metal, fatigue life of the welded joints was lower than the lives of samples without welds. In particular, the fatigue performance of overlap joints was very poor. This was presumed to be due to the changed material properties of the heat affected zone which was formed by the excess heat of the welding process as fractures often occurred at such locations. Based on experimental findings and fractographic observations, a clear adverse effect of welding process in material behaviour was discovered. Despite the concentrated heat of microplasma arc welding, post-weld heat treatment of the weld area is recommended to improve the mechanical behaviour of the welded joints.