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Knowledge of the kinetics of gas bubble formation and evolution under cavitation conditions in molten alloys is important for the control casting defects such as porosity and dissolved hydrogen. Using in situ synchrotron X-ray radiography, we studied the dynamic behaviour of ultrasonic cavitation gas bubbles in a molten Al-10 wt% Cu alloy. The size distribution, average radius and growth rate of cavitation gas bubbles were quantified under an acoustic intensity of 800 W/cm 2 and a maximum acoustic pressure of 4.5 MPa (45 atm).Bubbles exhibited a log-normal size distribution with an average radius of 15.3 ± 0.5 µm.Under applied sonication conditions the growth rate of bubble radius, R(t), followed a power law with a form of R(t)=αt β , and α=0.0021 & β=0.89. The observed tendencies were discussed in relation to bubble growth mechanisms of Al alloy melts.

Fast synchrotron radiography was used to investigate ultrasonic cavitation bubble formation and their dynamics during liquid metal processing of Al-Cu metal matrix nano composites (MMNC) in comparison with conventional alloys. The experimental observations showed enhanced cavitation potential in MMNC melts, due to the presence of Al 2 O 3 nano particles which believed to be acting as heterogeneous nuclei for bubble formation. Quantitative image analysis demonstrates that the addition of nano particles increases melt agitation partially, while introducing higher flow velocity variations across the melt. This suggests that the presence of nano particles may substantially alter propensity for ultrasonic treatment effects during solidification processing of MMNCs. Highlights• Fast X-ray imaging of ultrasound cavitation in Al-Cu metal matrix nano composite melts.• Nano particles significantly enhance the ultrasonic cavitation bubble formation potential.• Higher flow velocity variation across the melt with increased cavitation activity was found from the experimental observations.

A study has been carried out to understand the modification of alumina inclusions in an Al-Killed high sulphur steel with calcium treatment in 150 tonne steel ladle. To avoid abnormalities during casting, inclusions chemistry needs to be controlled so that these inclusions are in liquid phase during continuous casting of steel. For calcium treatment to be effective, general practice is to desulphurise the steel so as to reach sulphur levels below 0.010% to prevent formation of solid CaS inclusions that are harmful to steel quality and final properties. To avoid this additional desulphurising step which involves cost and is time consuming, the authors have developed a new approach of calcium treatment of steel at an industrial scale. This approach involves treating the liquid steel with calcium treatment at low aluminium levels which enables formation of liquid calcium aluminate inclusions (C 12 A 7 ) in the melt and then addition of sufficient aluminium for achieving grade requirement (i.e.

The present work deals with the effect of iron intermetallics on the microstructure and mechanical properties of Al-7% Si alloys. Two different iron additions were made, 0.6% Fe and 2% Fe, to study the effect of iron intermetallics on Al-Si alloys. Microstructure property correlations were carried out using SEM-EDS and tensile testing of alloys. Microstructure results show that the rise in iron content significantly increased the average size, thickness and number of intermetallic particles in the alloys. Nano-indentation study shows that the iron intermetallics are too brittle compared with the primary aluminium. Moreover, the hardness and Young's modulus of iron intermetallics are higher than those of primary aluminium. Tensile test results show that there is no significant difference in strength levels between Al-7%Si and Al-7Si-0.6Fe alloys. However, an increase in iron from 0.6% to 2% resulted in a significant decrease in tensile strength and elongation of the alloys. Two-dimensional SEM studies suggest that the increased number of needle-shaped b-phase intermetallic particles formed because of increased amounts of Fe could be the reason for early failure of the alloy. To further understand the early failure of iron-containing alloys, the fractured tensile specimens were studied using the 3D x-ray tomography technique. XCT results show that the failure in tensile testing of 2% Fe alloy was not mainly due to breaking of brittle b-phase intermetallic particles, but due to the morphology and particle-matrix interface debonding. XCT shows that the needleshaped particles are long, sharp-edged platelets in 3D, which act as stress raisers for crack initiation and propagation along the interphase.

Dissimilar joining of copper (C10300) to AISI-304 Stainless Steel (SS) sheets was performed using Electron Beam Welding (EBW) process. EBW was performed for two weld conditions such as with beam oscillation and without beam oscillation. X-ray Computed Tomography (XCT) technique was used for three-Dimensional (3D) visualization and quantification of porosity in the weld region. It was observed that the application of beam oscillation resulted in less porosity and the average pore size was found to be smaller as compared to without beam oscillation condition. Also, pores were found to be uniformly distributed in the weld incase of with beam oscillation as compared to without beam osicllaition condition. Further, it was observed that there exists an optimum beam oscillation diameter beyond which there is no positive effect of beam oscillation in controlling the porosity formation in the weld joint.