Natural ageing behaviour of cast alumina particle-reinforced 2618 aluminium alloy

The effect of the presence of 10 and 15 vol% alumina particles on the natural ageing behaviour of cast 2618 aluminium alloy was investigated using microhardness measurements and differential scanning calorimetry. It was found that the addition of the alumina particles does not alter the ageing sequence of 2618 AI although certain aspects of the precipitation reactions are changed. In particular, the relative quantities of the various phases were changed by reinforcement addition. Increasing the alumina content decreased the volume fractions of the Guinier-Preston-Bagaryatskii (GPB) I phases. Also, the peak reaction temperature, (T _p), for the GPBII and S phases decreased with increasing volume fraction of alumina.     

Effect of heat input on weld bead geometry of submerged arc welded ASTM A709 Grade 50 steel joints

A series of measurements was carried out on specimens of submerged arc welded plates of ASTM A709 Grade 50 steel to determine how variation in heat input achieved using single and double wires affected bead reinforcement, bead width, penetration depth, contact angle, heat affected zone (HAZ) size, deposition area, penetration area and total molten area. The level of dilution and different melting efficiencies were calculated and their variation with heat input was analyzed based on the acquired measurements. The cooling time from 800 to 500 °C was also related to various weld bead characteristics (e.g., total nugget area, heat transfer boundary lengths, bead width-to-depth ratio, and nugget parameter). The bead reinforcement, bead width, penetration depth, HAZ size, deposition area and penetration area increased with increasing heat input, but the bead contact angle decreased with it. The electrode melting efficiency increased initially and then decreased with increasing heat input, but the plate melting efficiency and percentage dilution changed only slightly with it. Cooling time exhibited a very good linear relationship with the total nugget area, heat transfer boundary length, and nugget parameter.     

The effect of cooling rate on the quench sensitivity of 2618 Al/Al2O3 MMC

Metal matrix composites (MMCs) are materials consisting of metal alloys reinforced with fibers, whiskers, particulates, and wires. Due to their superior mechanical properties, such as low coefficients of thermal expansion and high specific stiffness, they are attractive for many structural and non-structural applications. The most notable production applications are found in the aerospace, automobile, and sports equipment industries. Despite the great potentials possessed by MMCs, there are some concerns regarding the effect of the reinforcements, which are mostly ceramics, on the properties of the matrix alloys. One such property is the quench sensitivity of the matrix material. Heat treatable aluminum alloys are quench sensitive (i. e. their properties and precipitation behavior change with cooling rate or quenchant). The rate of cooling or the type of quenchant used during the fabrication process or the subsequent solution heat treatment affects the mechanical properties of these materials. Therefore, any modification that can alter the quench sensitivity significantly could have important consequences on the heat treatment of the alloys. Thus, the quench parameters may have to be more tightly controlled than for the unreinforced alloy in order to maintain consistent as-quenched properties. In the present study, the quench sensitivity of 2618 Al alloy and its composite containing 10 vol. % Al₂O₃ particles was investigated using hardness measurements and differential scanning calorimetry (DSC). Although 2618 Al is quench sensitive, its quench sensitivity was significantly increased by the addition of Al₂O₃ particles. Also, cooling rate affected the precipitation kinetics and the volume fraction of the precipitate phases formed in both materials.     

Internal cathodic protection to study the erosion-corrosion of AISI 1018 carbon steel

Steel elbows used in pipelines carrying potash slurry may undergo material loss due to mechanical erosion and/or electrochemical corrosion. Cathodic protection was used to study the effects of flow velocity and slurry concentration on the protection current density required to maintain AISI 1018 carbon steel elbows at a set electric potential. A flow loop with a peristaltic pump was used to pump a slurry consisting of silica sand in a saturated potash brine through the steel elbows. The protection current density measurements were performed under varying slurry flow velocities of 2.5, 3.0, 3.5, and 4.0 m/s and varying slurry concentrations ranging from 0-35 wt%. The results show maximum values of protection current density were required for mid-range slurry concentrations. It is concluded that, within the parameters of study, high flow velocities require higher protection current density than low flow velocities. Furthermore, high flow velocities result in a local maximum protection current density being reached at lower slurry concentrations; conversely, a local maximum protection current density is reached at higher slurry concentrations in lower flow velocities. The contrast in local maximum protection current densities likely occurs due to additional particle-particle collisions at higher velocities causing the maximum mass transfer rate of oxygen to be reached at lower slurry concentrations. SEM micrographs show that wear becomes more evenly distributed with increasing flow velocity due to the homogeneous distribution of particles in the flowing medium.     

Thermal diffusivity, thermal conductivity, and specific heat of flax fiber–HDPE biocomposites at processing temperatures

There is increasing work on the use of flax fibers as reinforcement for manufacturing composites because of their lower cost and environmental benefit. During manufacturing of such natural fiber–plastic composites, heat transfer is involved, but information about the thermal conductivity and thermal diffusivity at the processing temperatures is not available. In this study, the thermal conductivity, thermal diffusivity, and specific heat of flax fiber–high density polyethylene (HDPE) biocomposites were determined in the temperature range of 170–200 °C. The fiber contents in biocomposites were 10%, 20%, and 30% by mass. Using the line-source technique, the instrumental setup was developed to measure the thermal conductivity of biocomposites. It was found that the thermal conductivity, thermal diffusivity, and specific heat decreased with increasing fiber content, but thermal conductivity and thermal diffusivity did not change significantly with temperature in the range studied. The specific heat of the biocomposites increased gradually with temperature.     

The structure of Al x FeNi phase in Al-Cu-Mg-Fe-Ni alloy (AA2618)

The structure of the aluminide phase (Al _x FeNi) in cast AA2618 has been investigated by means of electron probe microanalysis and transmission electron microscopy techniques. The Al _x FeNi phase has been determined to have a C-centred monoclinic structure with lattice parametersa=0.8673 nm,b=0.9000 nm,c=0.8591 nm, and =83.504°. It is also shown that the structural formula of the phase varies from particle to particle and is influenced by the aluminium content.     

An investigation of the corrosion behaviour of a FeNiCoAlTa shape memory alloy in 3.5 wt-% NaCl solution

In this study, the corrosion behaviour of an FeNiCoAlTa (NCAT) shape memory alloy in 3.5% (w?w^?1) NaCl solution was evaluated. Linear polarisation resistance and potentiodynamic polarisation tests were conducted at 25°C. An open circuit potential (OCP) of ?381?mV (vs. saturated calomel reference electrode) and a corrosion rate (CR) of 0.0174?mm?y^?1 were obtained. The NCAT alloy did not show any passivation in the 3.5% (w?w^?1) NaCl solution. Its corrosion behaviour was very similar to that of G10180 (AISI 1018) carbon steel with the NCAT showing a lower CR and a less active OCP. Its corrosion in the solution was a combination of general dissolution and localised attack (pitting). Aging heat treatment caused β-Ni₃Al phase, and tantalum to precipitate on the grain boundaries, resulting in chemical species segregation between the grain boundaries and the grains. The chemical segregation caused intergranular corrosion of the alloy.     

Temperature effects on the chemical composition of nickel-phosphorus alloy thin films

Electroless Ni-P (EN) alloys are widely used as coating materials. Their properties depend on the level of phosphorus present and the extent of thermal treatment. We report the results of two complimentary electronic structure techniques, X-ray absorption near edge structure (XANES) and X-ray photoelectron spectroscopy (XPS), and the site-specific surface chemistry in EN alloys of different phosphorus compositions and thermal treatments. In XANES experiment, absorption at the Ni L_3,2 edge and the P K edge were measured and the P 2p, Ni 2p, and Ni 3p bands were measured by XPS. Heating EN alloys to high temperatures result in a competitive reaction between phosphorus and nickel on the surface for oxygen. There is an increase in the level of phosphates and other forms of phosphorus oxides and a decrease in the oxidized nickel on the surface of the EN alloy thin film. Changes in the electronic structure and chemical composition in the bulk of the EN alloy are not obvious.     

A calorimetric study of S′ and θ′ precipitation in Al2O3 particle-reinforced AA2618

Differential scanning calorimetry (DSC) was used to study the kinetics of S and precipitation in AA2618 and its composite containing 15 vol % Al₂O₃ particles . The unreinforced alloy and the composite were fabricated by a proprietary casting method, followed by extrusion. The DSC studies were carried out on as-quenched samples of the test materials. The precipitation of the S and phases in both materials was found to be kinetically controlled and obey the modified Avrami-Johnson-Mehl equation. The growth mechanisms for S and formation in AA2618 seemed unaffected by the addition of Al₂O₃ particles. The growth parameters obtained for the precipitation of these phases in the matrix alloy and the composite were not significantly different.