The impact of metal inert gas welding on the corrosion and mechanical behavior of AA 6061 T6

An attempt has been made to investigate the effects of MIG welding on the corrosion and mechanical properties of AA 6061 T6. A series of experimental techniques has been conducted to evaluate the corrosion and mechanical properties of the alloy. The corrosion media used was 3.5% (wt) NaCl. Polarization and open circuit potential tests were conducted by exposing various zones independently; therefore the reported corrosion results correspond to uncoupled condition. Different mechanical tests including tensile, torsion, and hardness were carried out; the same tests were also used for the un-welded specimens. The results show that the heat affected zone (HAZ) exhibited poor corrosion properties compared to the base metal (BM). The corrosion on both HAZ and BM was of pitting nature. More corrosion was observed on HAZ due to the thermal effects of the welding. Corrosion potential of HAZ was largely fluctuated comparing to BM with more negative peaks. The corrosion potential of the BM remained relatively steady over the whole immersion time. Welded specimens show lower mechanical properties comparing to non-welded specimens. The location of failure for welded and un-welded specimens after tensile test was found to be across the centre of the specimens. Welded tensile specimens have shown lower tensile strength. The location of the failure for welded specimens after torsion test was found predominantly along the HAZ which was attributed to the microstructural alteration that caused by the generation of heat during the welding process. Un-welded torsion specimens were failed near the centre line. Welded specimens exhibited lower torsion properties compared to the non-welded specimens with a reduction of almost 50%. The lowest hardness value was found across the weld centre.NPRP grant No. 09-211-2-089 from Qatar National Research Fund (a member of Qatar foundation).Scopu

Effect of hexagonal on the in-plane crushing behaviour of plain weave composite hexagonal quadruple ring system

In this study, an experimental investigation into the crushing behaviour of one dimensional composite hexagonal cellular structure between two plates has been carried out. The materials have been used to accomplish the studies are the plain weave E-glass fabric and the epoxy resin. The tested cellular structures are composed of 4 × 1 hexagonal cells with angles varied between 35° and 60°. Various crashworthiness parameters of the tested cellular structures such as crushing load capacity, energy absorption capability and force efficiency were computed and discussed. The crush failure modes of the tested rings were identified and analysed. Results showed that the hexagonal ring angle has a significant effect on the crush failure loads and energy absorption capability. Increasing the cell angle showed a decrease in energy absorption capability and load carrying capacity. Additionally, the cell angle has a remarkable effect on the failure sequence of the ring cells.Scopu

Corrosion behavior of friction stir welded lap joints of AA6061-T6 aluminum alloy

In this work, the corrosion behaviors of friction-stir lap welding of 6061-T6 Al-alloy are studied. The friction-stir lap welding was performed under different welding conditions (rotation speed and welding speed). The corrosion behavior of the parent alloy, the weld nugget zone (WNZ), and the heat affected zone (HAZ) of each welded sample working as an electrode, were investigated by the Tafel polarization test in 3.5 wt. (%) NaCl at ambient temperature. The morphology of the corroded surface of each region was analyzed by scanning electron microscopy together with energy dispersive spectroscopy (SEM-EDS). The results showed that the corrosion resistance of the parent alloy was better than the WNZ and the HAZ in both welding conditions. Localized pit dissolution and intergranular corrosion were the dominant corrosion types observed in the parent alloy, WNZ, and HAZ. The parent alloy, WNZ, and HAZ exhibited similar corrosion potentials (Ecorr) after T6 heat treatment. This treatment had a better effect on the corrosion resistance of the welded regions than the parent alloy

Salmonella Infections among Pediatric Population in Qatar: Phenotypic Resistance and Associated Genotypic Determinants

Salmonella is a significant public health burden worldwide and being the most common bacterial diarrheal illness among infants and young children. In the last few years, Qatar reports a high incidence of salmonellosis outbreaks coupled with a significant increase of Multidrug-Resistant (MDR) among pediatric populations every year. This study aims to elucidate the molecular mechanisms underlying resistance to ceftriaxone, cefepime, amoxicillinclavulanate tetracycline, trimethoprim-sulfamethoxazole, chloramphenicol, and azithromycin among Salmonella isolated from the pediatric population. A total of 246 Salmonella isolates were collected from children under 18 years old admitted to the Pediatric Emergency Center (PEC), Hamad Medical Corporation (HMC) from Jan. 2018 to Dec 2019 with gastroenteritis. Isolates were tested for antibiotic susceptibility against nineteen relevant antibiotics using E-test. Resistance was confirmed using PCR-specific primers for 38 genes. Resistance was detected against 14 antibiotics, and 38.2% of isolates were resistant to at least one antibiotic. Overall, we reported 23.9%, resistance to tetracycline 21.1%, ampicillin 18.7%, AMC, and 13% sulfamethoxazole-trimethoprim. Further, 16.2% of the isolates were Multidrug-Resistant (MDR), with 4.1% being Extended-Spectrum β Lactamase (ESBL) producers. 90% of ESBL producers harbored one of bla CTX-M-Group. Class 1 AMC resistant samples showed the highest resistance to different antibiotics. Our results indicate a high antimicrobial resistance pattern of Salmonella and the presence of Class (1) cassette that involves the transmission and expression of the resistance among AMC resistance isolates, which might lead to increased multi-drug resistance. This study provides evidence guidance to activate and implement the pillars of an antimicrobiThis work was supported by Qatar University collaborative grant no.: QUCG-BRC-19/20

Development of cost-effective composite repair system for oil/gas pipelines

Fiber-reinforced composite repairs are becoming widely used as an alternative to the installation of welded, full-encirclement sleeves for repair of oil and gas transmission/transportation pipelines. The primary advantage of this repair over welded, full-encirclement sleeves is that the need for welding is precluded. However, the composite repairs are fabricated by hand lay-up, which lacks fiber tension and resin content. A four-phase program to improve the pressure capacity of internally pressurized composite overwrapped damaged metallic pipes was undertaken. In the first phase, designing, fabricating of automated cost-effective composite repair system was carried out. The second phase focuses on the effects of composite overwrapped metallic pipes to understand the influence of fabric orientation angle on their responses of to the internal pressure. Phase three evaluates the improvement in pressure capacity of overwrapped damaged pipes by varying the fabric orientation. The fourth phase is devoted to investigate the corrosion resistance of the pipes. The results demonstrated the strong potential benefits of using new repair system. The fabric orientation of composite overwrapped exhibited a pronounced effect on the damaged pipes capability to carry high internal pressure. Composite overwrapped damaged metallic pipes exhibited high pressure capacity compared with externally damaged and non-damaged metallic pipes..Scopu

Study on the impact of welding on the corrosion properties of AA 6061 T6

Aluminium alloy 6061 T6 circular specimens were joined using TIG welding method. AlMg5 was used as filler. The corrosion behavior of welded and un-welded AA 6061 T6 was investigated using potentiodynamic and open circuit potential (OCP) measurements. Specimens were immersed in 3.5 (wt %) NaCl solution. Different zones with different corrosion properties were created as a result of the welding process. Results reveals that sever pitting corrosion has taken place on the heat affected zone (HAZ); the corrosion current of HAZ was increased. The measured potential of HAZ was more negative and largely fluctuated comparing to base metal (BM).Scopu

Tensile, hardness, and torsion behavior of welded AA

Tensile, Torsion, and Hardness behavior of welded and un-welded Aluminium Alloy 6061 T6 were investigated. Tests were conducted to evaluate the impact of tungsten Gas Arc welding (TIG) on some of the mechanical properties of the alloy. Different zones with different mechanical properties were created as a result of the welding process. Welding was found to have enormous impact on the tensile, torsion, and hardness properties of the alloy. Welded tensile specimens were failed at the welded area whereas not welded ones were failed at the centre. Welded torsion specimens were failed at the HAZ but not welded ones failed at the centre. The hardness of HAZ was decreased as a result of the heat generated during the welding process. Hardness values were increased as we moved away from the welded region. © (2014) Trans Tech Publications, Switzerland

Permeation of different cations through cathodically protected coated API X-120 steel at elevated temperature

The electrochemical behaviour of coated API X-120 steel in 0.5M of NaCl and KCl with and without cathodic protection (CP) at elevated temperature was investigated. CP was applied at -0.78 and -1.1V vs Saturated Calomel electrode (SCE) on day 5 of immersion. Temperature of solutions was set at 50 °C. Electrochemical Impedance Spectroscopy (EIS) was used to characterize the coating. Energy Dispersive X-Ray Analysis (EDAX) was used to map the metal surfaces. Visual inspection was used to support EIS data. The extent of corrosion was evaluated using Image tool analysis. A correlation was found between the size of the cations and the performance of the coating. Mapping of metal surfaces showed dense areas of Na+ and K+ at -1.1V. K+ was found to be faster than Na+ due to its smaller hydrated size

Effect of temperature and erosion on pitting corrosion of X100 steel in aqueous silica slurries containing bicarbonate and chloride content

The effect of temperature on erosion-enhance pitting corrosion behavior of X100 steel has been investigated. Tests were performed at two temperatures with the help of open circuit potential (OCP), potentiodynamic polarization scan and electrochemical frequency modulation. A heating plate was used to change and maintain the temperature of electrolyte during electrochemical tests. During zero and low erosion rates, the OCP decreases with increase of temperature. In contrast, during high erosion rate, the OCP first decrease and then increases. The few higher values than the normal values of 2 and 3, both causality factors gave mainly lower values during pitting corrosion.Qatar National Research Fund (QNRF) under National Priority Research Program (NPRP) No. 08-159-2-046.Scopu