Effects of Precipitation Hardening on Mechanical Properties of Multistage Stirred Cast AA6063 Composites

This research work is to study the effects of precipitation hardening on multistage stirred cast alumina reinforced AA6063 composites which were achieved through production of alumina (Al2O3) reinforced AA6063 alloy, using four stage stir casting method; determination of the effect of precipitation hardening heat treatment on the samples produced; and characterization of the microstructures and some mechanical properties of the cast and precipitation hardened aluminium matrix composite.This work studied the effects of precipitation hardening on multistage stirred cast alumina reinforced AA 6063 composite through production of alumina reinforced AA6063 alloy by four stage stir casting method, determination of effect of precipitation hardening heat treatment and characterization of microstructures and some mechanical properties of as-cast and heat treated samples of aluminium matrix composites. The amounts of AA 6063 and alumina particles required for the production of aluminium composites with 0, 3, 6, 9, 12 and 15 volume percent of alumina were determined by charge calculations. The particles of alumina were initially pre- heated at 300 oC to enhance wetability with aluminium alloy. The AA 6063 alloy was charged into a gas fired crucible furnace and the liquid was allowed to cool to a viscous mass at temperature of about 600 oC so as to introduce alumina particles. Stirring operations were performed manually and mechanically at 750 oC and 300 rpm, to ensure uniform distribution of reinforcement within the matrix, before pouring into permanent metal mould. The samples produced were solutionized at 550 oC for one hour, quenched in water and later aged at 180 oC for 2, 3 and 4 hours. Some samples were reserved for control experimentation. Mechanical responses of the composite were investigated by tensile, hardness and impact test carried out on the samples. The structures of the samples were examined by optical and scanning electron microscopes. The results trend showed that as the volume fraction of alumina and aging time increase, the strength and hardness values also increase with corresponding decrease in impact value. Composite with 15% alumina aged at 4 hours showed highest strength and hardness values of 262.77 MPa and 64.12 BHN, respectively with impact value of 9.86 J. The study showed that multistage stir casting method and precipitation hardening heat treatment are capable of improving the mechanical properties of AA 6063-Al2O3 composites.Self-sponsore

Fabrication of forced air cool austempered ductile iron and exploring its corrosion behaviour in a simulated mine water

Abstract: The production of austempered ductile iron (ADI) with uniform microstructure and properties is constrained by the austempering process vis-à-vis the quenching medium. This is as a result of the stringent operating parameters with costly facilities. This limitation has restricted the application of ADI, despite its inherent mechanical and chemical properties. An emerging technology of overcoming this limitation is by austempering with force air cooling equipment, which is accessible, available and cost-efficient. This work characterizes the behaviour of the forced air cool ADI in simulated mine water due to the strategic importance of the mining industry in the global economy. The study establishes the influence of sample section thickness on the corrosion performance. The sample’s thickness were 5, 15, and 20 mm. Electrochemical experiments were performed on the forced air cool ADI at atmospheric pressure and room temperature with method such as open circuit potential (OCP). The post-corrosion analyses were performed using X-ray diffractometry (XRD) and field emission scanning electron microscopy (FESEM). The research highlighted that small section thickness has a more favourable performance compared with larger section. Consideration is also accorded to the capability of the ADI in the studied environment

Microstructural characterisation of inertia friction welded RR1000 superalloy

The need for jet engines to burn fuel more effectively at higher temperatures requires the development of nickel-based superalloys containing increasing amounts of the main strengthening, stable, ordered L1$_2$ intermetallic (Ni$_3$(Al, Ti)) $\gamma$' phase, with RR1000 being a candidate. Welding of this alloy by conventional methods has been found difficult due to a high susceptibility to heat affected zone (HAZ) liquation cracking. In order to produce welds with good joint integrity, inertia friction welding (IFW), a nominally solid state welding process, has been used to join gas turbine parts made from this alloy, based on the premise that the joining occurs below the melting point of the bulk material. The failure rate, however, is not zero. Detailed microstructural characterisation of the actual weld and of a thermo-mechanically simulated HAZ has revealed for the first time that non-equilibrium constitutional liquation of some strengthening precipitates occurs at the grain boundaries and within the grains of this alloy during IFW, with attendant formation of liquation microvoids within the HAZ. The temperature gradient across the HAZ is predicted to be 1150 $^o$C-1286 $^o$C. Hafnium-rich oxides were also found to coalesce and become smeared by friction along the weld interface, forming brittle hafnium oxide flakes. However, IFW has been found to be more effective than conventional welding techniques, always producing liquation crack-free welds within 150 $\mu$m of the bond line (not common in conventionally welded alloys). Micro tensile testing was used to characterise the local strength within the weld and to rationalise it with the microstructure.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

STRUCTURAL ANALYSIS OF A LIGHTWEIGHT ELECTRIC VEHICLE CHASSIS: Received: 08th April 2024 Revised: 17th May 2024, 21st May 2024, 23rd May 2024 Accepted: 01st May 2024

This study presents a comprehensive investigation into the design and structural analysis of lightweight chassis for electric vehicles. A chassis needs to be able to withstand twist, shock, vibration, and other stresses caused by acceleration, braking, road condition, and shock initiated by other parts of a vehicle. It should carry a maximum load under all operating conditions. Two materials, 304L steel, and Ti-6AL-4V alloy were evaluated, with parameters such as total deformation, equivalent stress, and equivalent elastic strain under consideration. The outcome of the Finite Element Analysis revealed that Ti-6AL-4V can withstand higher stresses than 304L Steel. By investigating the static behaviors of the chassis under static loading due to weight and overload conditions, Ti-6AL-4V was chosen as a suitable replacement for a 304L Steel chassis

Microstructural characterization and corrosion behaviour of heat treated standard stainless steels in tar sand

This paper aims to investigate the corrosion behaviour of heat-treated standard duplex stainless steel (UNS S32205) in the recovery of bitumen from Nigerian-rich tar sand, using sodium hydroxide (NaOH) as the process solution. Appropriate material family needs to be identified for the exploitation of tar sand resources to ensure sustainable extraction of bitumen. UNS S32205 offers exceptional mechanical properties and excellent corrosion resistance which makes it a great material choice for demanding applications, including offshore platforms and construction projects. Samples of UNS 32205 were heat-treated and immersed in the digested tar sand, maintaining a process temperature of 90°C. The microstructure of the corrosion coupons was studied using SEM/EDS (Scanning Electron Microscope/Energy Dispersive Spectroscope), and the corrosion rate of the samples was derived using gravimetric technique following ASTM G31 standard. The SEM micrographs indicated varying degrees of pits associated with the passivity of UNS 32205 and an imbalance between its ferrite and austenite phases due to the presence of secondary precipitates formed during heat treatment.The normalized sample, having a corrosion rate of 0.053 mm/year, exhibited the best corrosion resistance, followed by oil quenching (0.054 mm/year), then annealing (0.076 mm/year), and water quenching (0.077 mm/year), where they all showed improved corrosion resistance over the as-received sample having a corrosion rate of 0.078 mm/year