H.R. Ammar

Effects of Physical Properties of Anode Raw Materials on the Paste Compaction Behavior

The current study investigates the effects of coke particle characteristics and paste formulation on the flowability and the compression behavior of anode pastes. Shape factor and texture of different fractions of cokes were characterized using an image analysis system where the characteristics of each coke were correlated to its vibrated bulk density (VBD). A compression test was designed to study the effects of particle characteristics and paste recipe on the compactability of pastes. The test was applied on four anode pastes, prepared from different coke types, particle size distributions and pitch contents. It was observed that the compression test is significantly sensitive to any changes in raw materials characteristics and formulations. Consequently, the compression test may be used as a tool for evaluating anode quality in relation with material variations.

Influence of Mixing Parameters on the Density and Compaction Behavior of Carbon Anodes Used in Aluminum Production

The current study investigates the effects of mixing parameters on the quality of anode paste and green anode used in aluminum electrolysis. Four mixing times and four mixing temperatures were applied to prepare anode pastes using calcined petroleum coke and coal tar pitch, as raw materials. The volume of the pores in the paste was used as the indicator for mixing effectiveness. A compression test was applied to the pastes to study the compactability of these pastes and to investigate the effect of mixing parameters on density of the green samples. It was shown that mixing parameters influence the size, volume and surface area of paste porosity and also its compaction behaviour.

Metallographic investigation of tensile- and impact-tested aluminum composites

The present work was performed on two composites: Al-15 vol.% B4C and experimental 6063/15% B4C. Additions of 0.45% Ti + 0.25% Zr were made to both composites melts. The composites were cast from the respective melts at 730℃ using two metallic molds to produce tensile as well as impact test samples. All samples were solution heat treated for 24 h at 540℃ for both composites, followed by aging at 200℃ for 10 h. Samples for microstructure and fractography were examined using field emission scanning electron microscopy. The results show that the powder injection technique used in this study produces composites with B4C uniformly distributed throughout the matrix. The strength and impact toughness of the two composites are controlled by the simultaneous precipitation of Al3Zr and Mg2Si phase particles depending on the matrix type. Hardening caused by precipitation of Mg2Si is more pronounced than that caused by Al3Zr phase precipitation. No B4C particle debonding was observed due to the presence of Zr-/Ti-rich layers surrounding the B4C particles. The cracks mainly propagate through the B4C reinforcement particles.

Effect of testing temperature on the strength and fracture behavior of Al-B4C composites:

The present study was performed on two Al-10 vol. % B4C composite containing in common 0.48%Ti and 0.25%Zr. The matrix in the first composite was commercially pure aluminum and in the other was experimental 6063 alloy. The molten composite was cast in the form of slabs (25 × 20 × 400 mm). Prior to hot rolling, the slabs were annealed at 540℃ for 16 h and the last two rolling passes were done at room temperature. Final sheet thickness was about 2 mm. Samples for tensile testing were prepared from the rolled sheet using wire cutting technique. The tensile samples were solution heat treated at 540℃ for 8 h followed by furnace cooling. Samples for microstructure as well as fractography were also examined. Tensile samples were tested in the temperature range of 25–500℃ at a strain rate of 5 × 10−4 s−1. The results show that when composite samples were tested following solution heat treatment, the role of the matrix composition in controlling the preservation of the composite strength at high temperature is nil. Increasing the testing temperature caused rapid decrease in the composite strength in a non-linear pattern. The fracture surface of the deformed composites consisted mainly of well-defined dimple structure. The size of these dimples is a direct function of the testing temperature. The presence of Ti-Zr rich protecting layers surrounding the B4C particles resulted in good particle/matrix wettability throughout the entire testing temperatures (25–500℃). Cracks were observed to be initiated at the particle/matrix interface and propagate through the B4C particles. The length of crack propagation was mainly dependent on the particle size. Increasing the testing temperature appeared in the gradual fracturing of the reinforcement particles.

Effect of different compaction and sintering conditions on the thermo-mechanical properties of bulk aluminium produced using mechanical alloying

Abstract In the investigation reported here, coarse-grained Al powder (85 μm) was subjected to ball milling for 4 h in an attritor at room temperature under argon atmosphere. The bulk aluminium samples consisting of ultrafine and nanocrystalline grains were prepared from ball-milled powders using a high frequency induction sintering machine. The bulk samples were investigated for the enhancement in mechanical properties using uniaxial compression experiments to large strains. Vickers micro hardness measurements were made along the diametral line of the bulk samples. A comparative study on the effect of mechanical properties of bulk samples obtained through different processing conditions was addressed and an optimum processing condition is established. The variation in strain-rate sensitivity with different processing conditions of the bulk samples was also investigated.

Effect of Consolidation and Sintering Parameters on the Mechanical Responses of Nanocrystalline Al-Fe Alloy Processed by Mechanical Alloying

In this investigation, bulk ultra-fine grained and nanocrystalline Al-2 wt.% Fe alloy was produced by mechanical alloying (MA). The powder was mechanically milled in an attritor for 3 hours and yielded an average crystal size of ~63 nm. The consolidation and sintering was performed using a high frequency induction sintering (HFIS) machine at a constant pressure of 50 MPa. The prepared bulk samples were subjected to uniaxial compressive loading over wide range of strain rates for large deformation. To evaluate the effect of sintering conditions and testing temperature on the strain rate sensitivity, strain rate jump experiments were performed at high temperature. The strain rate sensitivity of the processed alloy increased with an increase in temperature. The density of the bulk samples were found to be between 95 to 97%. The average Vickers micro hardness was found to be 132 Hv0.1.