Pitting Corrosion in AA7075 Friction Stir Welds on Minor Additions of Silver

AA7075 is extensively used in aerospace, defense, automotive applications because of its high strength to weight ratio. Issues related to fusion welding and corrosion resistance are key problems associated with these alloys. Friction stir welding is an alternative welding technique that overcomes problems associated with fusion welding. In the present investigation, preliminary studies were done on pitting corrosion behavior of AA7075 friction stir welds by adding silver along the weld joint line. Silver paste was applied along the longitudinal direction of AA7075-T6 rolled plates of 6-mm thickness and cured at 130 °C for 30 seconds. Weld joints were prepared at two different tools rotational speeds, i.e., 750 rpm and 1000 rpm, while keeping other parameters fixed. Welded joints were cut as per the required sizes to study the hardness, microstructure, and pitting corrosion resistance in various regions. It was observed that the hardness was not much affected, but pitting corrosion resistance substantially improved by trace addition of silver. In the stir zone and the thermo-mechanically affected zone, onion ring type marks were observed. Grain refinement in the stirred zone (SZ) was higher at 750 rpm compared to 1000 rpm. The increased hardness in the welds was due to grain refinement. All the observed results were correlated with microstructural features as evidenced by optical microscopy.

Experimental investigation on friction stir welding of dissimilar aluminium alloys

In current research work, dissimilar aluminium alloys such as AA5083, AA6081, AA6082, and AA7039 are butt joined by employing friction stir welding (FSW). The present study explores the effect of material positions of aluminium alloys (i.e., advancing side (AS) and retreating side (RS)) on the mechanical and metallurgical properties of FS welded dissimilar aluminium joints. The performance characteristics of the present study are analyzed in terms of mechanical and metallurgical properties. It is concluded that maximum strength is obtained for all the joints in which higher strength aluminium alloy is placed on the AS ((i.e., 386 MPa for AA7039-AA5083, 343 MPa for AA7039-AA6082, 320 MPa for AA5083-AA6082, and 225 MPa for AA6082-Aa6061). Furthermore, two types of macrostructures (i.e., banded and an onion ring) are observed at the nugget zone (NZ) of all the welded joints during metallurgical analysis. Besides this, energy-dispersive X-ray spectroscopy (EDS) analysis at NZ of FSW joints is also carried out to find out the chemical composition at NZ. It is observed that the key element of AS material is high er in weight percent as compared to RS at NZ. Moreover, tensile fractured surface locations are also analyzed to understand the process better. It is witnessed that most joints are fractured at heat affected zone (HAZ) on the lower strength material side.

Effect of tool offset on microstructure and mechanical properties of dissimilar copper-brass friction stir welding

This study has investigated the effect of tool offset on the mechanical behavior and microstructure of dissimilar copper and brass joints by friction stir welding (FSW). In this regard, the FSW method was used for joint with three different tool offset positions, namely center line (no offset), the copper side, and the brass alloy side. Microstructure and fracture surfaces of the specimens were examined by optical (OM) and scanning electron microscopies (SEM), respectively. Tensile, micro-hardness and bending tests were also utilized to evaluate the joints mechanical behavior. The results showed that an onion ring-shaped zone was formed with the tool offset towards the copper side, but this zone was not observed with the tool offset towards the brass alloy side. In addition, compared with the tool without offset, the tensile strength with the tool offset to copper side of 1 mm (Cu+1) increased by 33.33% and with the tool offset to brass alloy side of 1 mm (Brass+1) increased by 57.47%. The results of bending test showed that in the Brass+1 specimen, bending strength increased by approximately 5% compared with the specimen without offset. Finally, it was found that the best mechanical and microstructural properties were obtained by the tool offset of 1 mm towards the brass alloy side.

Microstructure and Mechanical Properties of 6061 Al/AZ31 Mg Joints Friction Stir Lap Welded by a Tool with Variable-Pitch Thread Pin

Sheets of 6061-T6 aluminum alloy (thickness = 3 mm) and AZ31 magnesium alloy were friction stir lap welded by a tool with a variable-pitch thread pin (coarse-threaded in the upper part and fine-threaded in the lower part). For the same rotation speed and welding speed, the heat input was higher in joints with an upper Al alloy (Configuration Al-Mg) than in those with an upper Mg alloy (Configuration Mg-Al). In Configuration Al-Mg, these two dissimilar metals were poorly mixed and Al dominated the stirred zone (SZ). Many intermetallic compounds (IMCs) of Al3Mg2 formed inside the SZ. In Configuration Mg-Al, Mg alloy bands, flocculent Al12Mg17 bands, and minor Al alloy bands intersected in the SZ, forming a complex onion-ring structure. Moreover, a complex mechanical interlocking structure developed at the bottom interface of the SZ. The maximum tensile shear strengths of the Al-Mg and Mg-Al lap configurations were 160.3 and 217 N/mm, respectively, at 700 rpm. The higher tensile shear strength of the Mg-Al configuration primarily represented less IMCs and complex mechanical interlocking structures in the SZ.

Assessing Microstructure-Local Mechanical Properties in Friction Stir Welded 6082-T6 Aluminum Alloy

The severe deformation and temperature paths in the stir zone, also called weld nugget, of friction stir welded joints result, at very local levels, in significant microstructural variations, such as major differences in grain size or precipitation. One of the most common features of friction stir welds is the presence of successive material layers, known as onion rings; however, little data is available on the mechanical properties of the different regions of the weld nugget, and particularly within the onion ring bands. Such information becomes very important for the integrity of large size friction stir welded structures. In the present study, a comprehensive characterization of onion rings produced during friction stir welding of a 6082-aluminum alloy was carried out. Advanced techniques such as in-situ SEM nanoindentation, EBSD, and high-resolution EDS were used to validate and compare the characteristics of the different bands in the onion rings. The analyses consisted of quantifying variations in grain size, precipitate composition and distribution, crystallographic orientations, and mechanical properties in each band. Furthermore, the tensile strengths of different regions of the weld nugget were evaluated using shear punch testing and correlated with those for the onion ring region in order to determine the impact of the presence of onion rings on weld nugget mechanical properties. The main difference between the alternate bands in the onion ring was found to be due to the difference in their grain size, misorientation, and precipitate content. It was also observed that the bands originate from the base metal and stir zone successively due to the nature of the stirring process, which pulls BM into SZ. Comparison of the shear punch testing results in different regions of the nugget revealed that, in spite of having local differences in the hardness of alternate bands in the onion ring, the presence of onion rings has no significant impact on the deterioration of the mechanical properties of the weld nugget.

A Criminological Examination Of The Use Of Cyberspace To Traffic Drugs In Durban South Africa

This study focused on the use of cyberspace to traffic drugs in Durban, South Africa. The study seeks to determine how cyberspace is used as a tool to traffic drugs in Durban, South Africa; to investigate the current South African laws as deterrence to combat drug trafficking via cyberspace. The studyused the qualitative research method. The data was collected from a sample consisting of eight respondents using the purposive sampling technique. The researchers collected data using semi-structured interviews and the collected data was analyzed through thematic content analysis. The findings depicted that cyberspace is used as a tool to traffic drugs in Durban by providing cyberspace users with the platform to engage in unlimited and secure communication. The use of Virtual Private Networks and The Onion Ring makes it exceptionally difficult to trace cybercriminals. Recommendation: There is a need for more awareness around cybercrime and, more particularly, drug trafficking via cyberspace. More law enforcement officers should be provided with training regarding cyberspace and drug trafficking via cyberspace.

Microstructure evolution mechanism of Al/Mg dissimilar joint during friction stir welding

A butt friction stir welding (FSW) process was performed on 6061 Al and AZ31 Mg plates. The microstructure evolutions of the three main regions in the nugget zone (NZ) retained in the FSW joint were systematically investigated to clarify the joint formation mechanism during FSW. The differential etching of these microstructural features was found to produce very vivid flow features. During FSW, the material in the shoulder affected zone (SAZ) was mainly driven by the shoulder, and only a small amount of it was driven by the pin. A strip of Al transferred by the pin from the retreating side (RS) to the advancing side (AS) contacted and reacted with Mg, thus forming intermetallic compounds (IMCs) (e.g., Mg17Al12 and Al3Mg2). Due to the stirring action and tilted angle of the threaded pin, a banded structure (BS) feature tilted at approximately 45° was produced by the alternating lamellae of IMCs. The appearance of an onion ring structure occurred in the severely deformed zone (SDZ), which could be attributed to the reflection effect of the imaginary die wall. Finally, the overall flow pattern of the joint was obtained.