Mamookho Elizabeth Makhatha

Effect of process parameters on the microstructure, hardness and wear resistance properties of Zn-Sn-Ti coatings on AISI 1015 steel: laser alloying technique

The deterioration of materials during industrial application poses a serious threat to the materials structural integrity. A materials susceptibility to wear and surface damage can be reduced by alteration of its surface chemistry, morphology and crystal structure which plays an important role in optimising a materials performance for a given application. The aim of the research was to investigate the enhancement in the microstructure and wear property of Zn-Sn-Ti ternary coatings on AISI 1015 steel by laser alloying technique using Ytterbium laser system (YLS). A laser power of 750-900 W, scanning speeds of 0.6 and 0.8 m/min, and alloy compositions of 25Zn-25Sn-50Ti and 20Zn-20Sn-60Ti were used in this study. At optimum composition of 20Zn-20Sn-60Ti and speed of 0.8 m/min, there was enhancement of 24% in wear resistance performance which was attributed to metastable intermetallic phases. The coatings were free of cracks with homogeneous and refined microstructures and good adhesion to the substrate. The response surface model (RSM) used authenticates reasonably with the experimental results.

Effect of process parameters on tensile strength and morphology of friction stir spot welds of aluminium and copper

Friction stir spot welding (FSSW) is a solid-state welding process used for joining similar and dissimilar materials. AA1060 and C11000 sheets were joined using different process parameters and tool geometries. The presence of a copper rings also called hooks were observed in all the produced spot welds and their length increases with the tool shoulder plunge depth; whereas the spot welds produced at 1200 rpm for the two tool geometries exhibited a decrease and a slight increment in the length of the copper ring using a flat pin/flat shoulder and conical pin/concave shoulder, respectively. Furthermore, the mapping of the produced spot weld using energy dispersive spectroscopy (EDS) exhibited different microstructures with the presence of copper fragments and particles in the aluminium matrix. It was also observed that, the shoulder plunge depth had an effect on the shear tensile results, except for the weld produced at 800 rpm when using a conical pin and a concave shoulder.

Microstructure and electrical resistivity properties of copper and aluminium friction stir spot welds

Dissimilar metal joining methods are essential for the manufacturing of a various structures and parts in the industries. Friction stir spot welding process was performed on 3 mm thick AA1060 and C11000. This paper presents the results on the microstructure, chemical analysis and electrical resistivities of the produced joints. The microstructure showed a contrast between the two different materials namely copper and aluminium and the presence of a copper ring (hook) in all the produced spot welds. The presence of copper particles in the aluminium matrix was observed in most of the welds. The conducted energy dispersive spectroscopy (EDS) analysis confirmed the presence intermetallic compounds. It was observed that, the spot weld produced using 800 rpm and 1 mm shoulder plunge depth exhibited a low electrical resistivity value of 0.009 µΩ, which shows an appreciation of 0.011 µΩ (55 %), compared to the average of the parent materials (0.020 µΩ). This could be an attractive option for electrical applications.

Friction Stir Welding and Friction Stir Spot Welding of Aluminium/Copper Alloys

The development of laboratory work on friction stir welding (FSW) and friction stir spot welding (FSSW) FSW of dissimilar materials should provide a good insight into their possible industrial applications; and therefore, enhance their industrial development. Many applications in various industries, especially in the manufacturing sector, have led to the development of processes, such as FSW and FSSW for similar and dissimilar materials. Aluminium and copper have different properties including melting temperatures, which make the two materials difficult to join. Choosing suitable parameters, such as rotation speed, welding speed, and tool plunge depth and dwell time is important when fabricating sound FSWelds and FSSWelds. This chapter presents the current state of FSW and FSSW of aluminium and copper. An overview of the research conducted in the field of FSW and FSSW between aluminium and copper is summarized in terms of the microstructural evolution and the mechanical properties. The quality of the fabricated welds, spot welds and explanations of various properties of the welds by various researchers is presented and summarized. This could provide an insight into the current state of the two processes; and it could also lead to the optimization of the techniques by conducting more research in the field of FSW and FSSW Al/Cu. Furthermore, future scope on the usage of the two techniques is addressed.

Microstructure and Chemical Analysis of Friction Stir Spot Welding Between Aluminium and Copper (Case Study)

The Friction stir spot welding technique was used to produce lap spot welds of AA1060 and C11000. Various process parameters and tool geometries were used to fabricate the welds. The microstructures of the produced spot welds produced were examined by using optical microscopy (OM) and scanning electron microscopy (SEM). The chemical analysis of the cross sections of the welds was investigated by using energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). A good Al/Cu material mixing was observed in most of the fabricated spot welds. The presence of copper rings on both sides of the keyhole with different lengths was observed in all the spot welds. The mapping using energy dispersive spectroscopy of a region of the keyhole/copper rings and the stir zone showed the presence of copper particles in the aluminium matrix. However. Very few aluminium particles were found in the copper rings. Intermetallic compounds were found in some of the spot welds.

Friction Stir Welding and Friction Stir Spot Welding of Similar Aluminium and Copper Alloys

Friction stir welding (FSW) and friction stir spot welding are solid state joining processes employed for the joining of similar and dissimilar materials. The processes are used by many researchers; because these processes produce sound welds; and they do not have common welding problems, such as solidification and liquefaction cracking related to the fusion welding methods. FSW and FSSW of similar aluminium and copper gained ground in the development of solid state joining processes. It may be observed that for FSW and FSSW of similar copper, many research studies were carried out using pure copper as the parent material. Whereas, for similar aluminium, almost the entire aluminium alloy series is utilized. Good quality joints with enhanced properties have been produced; and more studies are required, in order to fully optimize these processes. This could be beneficial in curbing global warming; since FSW and FSSW are both labelled as being environmentally friendly joining processes. In this chapter, FSW and FSSW research studies on similar aluminium and copper are briefly summarized in terms of the process parameters, the microstructural evolution and the mechanical properties.

Microhardness Profile and Shear Tensile Test of FSSWelds AA1060 to C11000 (Case Study)

Friction stir spot welding (FSSW) is a solid state welding process; and it is used to overcome the difficulties of joining aluminium and copper alloys. Dissimilar joining of AA1060 and C11000 using friction stir welding was carried out. The microhardness profile analyses were carried out and the probability distribution function (PDF) of the measured microhardness values was determined. Additionally, shear tensile tests were conducted. High microhardness values were obtained in the region close to the keyhole of most of the samples, which could be linked to the presence of intermetallic compounds in the stir zone of the spot welds. For the shear tensile test, only a nugget pull out failure mode took place in all the produced spot welds. The PDF revealed that the process parameters and the tool geometries significantly have an effect on the distribution of the microhardness values.

Residual Stresses in Friction Stir Spot Welded AA1060 to C11000 Using the X-Ray Diffraction Technique (Case Study)

Aluminium and copper are widely used in engineering structures, due to their unique performances, such as higher electrical conductivity, heat conductivity, corrosion resistance and mechanical properties even though they have considerable differences in their melting points. In this study, the microstructure of the friction stir spot welds of aluminium and copper produced at various parameter combinations were analyzed by using a scanning electron microscope; while the residual stresses were studied by using the X-ray diffraction technique. Furthermore, the electrical resistivities of the joints was also measured. The evolving microstructure shows a good mixing in the produced spot welds with Cu particles present in the aluminium matrix. The formation of a copper ring/hook was evident in all the spot welds; and the length thereof increased with the shoulder plunge depth variation; while the spot welds produced at 1200 rpm for the two tool geometries exhibited a decrease and a slight increment in the length of the copper ring using a flat pin/flat shoulder and conical pin/concave shoulder, respectively. The obtained residual stresses results were compressive. The maximum residual stress of −116.8 MPa was measured on the copper ring of the welds produced at 800 rpm and 0.5 mm shoulder plunge depth, when using a flat pin and a flat shoulder tool. This was due to the generation of stress, when the copper was extruded into the aluminium sheets. Furthermore, the intensity of all the peaks using different process parameters decreased in comparison to the peaks generated by the parent materials and the effect of shoulder plunge depth on the full width at half the maximum (FWHM) was observed. The values of the measured electrical resistivities of the joints were higher than those of the parent materials.

Waste Foundry sand Mineralogical Characterisation: The Impact of Cast Alloy, Casting Temperature and Molding Additive on the Nature Waste Foundry Sand

Abstract. The metal casting industry discharges huge volumes of waste foundry sand yearly. It was estimated to be 250 thousand tons of spent silica foundry sand for the existing 200 casting facilities in South Africa. Even though, establish documents exist in regards to the foundry sand composition, few well documented theories are available in regards to changes or mutations taking place after casting process. Four waste silica casting sands were qualitatively analyzed for they mineralogical phases composition using the X-ray diffraction (XRD). The investigation was conducted on various waste casting sand alloy including aluminum, cast iron, high chrome and steel. The result revealed a significant compositional difference related to the molding binder and casting temperature. Different silica phase’s polymorph, related to the various alloy casting temperature, were observed in waste sand samples. Theses phases included alpha quartz, tridymite, and alpha cristobelite. The molding binder favored the crystalisation of bentonite related mineral such as periclase, microcline and wustite, within the greensand system. The chemically bonded sand exposed the presence of anorthite as the only existing mineralized phase in the resin sand. The mineralogical content of the waste foundry sand provides information on the molding binder used. In addition to that, silica polymorph it informs about the pouring temperature related to the cast alloy.