Grain Refining Efficiency of SHS Al-Ti-B-C Master Alloy for Pure Aluminum and Its Effect on Mechanical Properties

A new Al-5Ti-0.75B-0.2C master alloy was successfully prepared by self-propagating high-temperature（SHS）reaction from an Al-Ti-B_4C system with molten Al.Microstructure and phase characterization of the prepared Al-5Ti-0.75B-0.2C master alloy show that the nearly spherical TiC particles,hexagonal or rectangular TiB_2 particles,and blocklike TiAl_3 particles distribute uniformly in the aluminum matrix.Grain refining test on commercial pure aluminum indicates that Al-5Ti-0.75B-0.2C master alloy exhibits a better grain refining performance than Al-5Ti-lB master alloy.By addition of 0.2 wt%Al-5Ti-0.75B-0.2C master alloy,the average grain size of a-Al can be effectively refined to160 ± 5 μm from about 3000 μm,and the tensile strength and elongation are increased by about 20%and 14.1%due to the grain refinement.

High Temperature Property Development of Bauxite Based Bricks

Physical properties and microstructural evolution on firing of 3 types of bauxite based refractory bricks were carried out using techniques such as porosimetry, XRD and SEM. The groups differed from each other by progressive refining of the matrix or bond phase. It is revealed that such a refinement of the matrix can improve the high temperature properties of the bricks made from poor grade materials .

Effects of Nd on microstructure and mechanical properties of as-cast Mg-8Li-3Al alloy

Effects of Nd on microstructure and mechanical properties of as-cast Mg-8Li-3Al alloy were investigated by OM,X-ray diffraction（XRD）,EPMA,scanning electron microscopy（SEM） and energy dispersive spectroscopy（EDS）.The results showed that the dendrites sizes of α phase were decreased by the Nd addition.When the amount of addition Nd was 1.6 wt.%,the alloy with the smallest α phase was obtained.The refining mechanism mainly owed to the increasing constitutional supercooling at the solidification front.Furthermore,the compound Al 2 Nd generated by the reaction of Al and Nd,which distributed at the phase boundary and inside β phase,could also restrain the growth of α phase.Nd could improve the tensile strength and elongation of Mg-8Li-3Al alloy,however,excessive Al 2 Nd might also become crack source and decrease the elongation.

Characterisation, Luminescence and Antibacterial Properties of Stable AgNPs Synthesised from AgCl by Precipitation Method

Silver nanoparticles （AgNPs） were synthesised using equimolar concentrations of redtlcing agent vitamin C and AgCl precursor by simple precipitation method. The synthesised AgNPs were characterised by X-ray diffraction （XRD）, UV-Visible, photoluminescence and field emission scanning electron microscopy （FESEM） analysis. The formation of AgNPs was confirmed by the typical surface plasmon resonance band at 426 nm. The presence of elemental silver and pure crystalline face centre cubic （fcc） structure was confirmed by energy dispersive X-ray analysis and XRD analysis, respectively. The FESEM images showed the formation of spherical AgNPs for lower concentrations （0.1 and 0.3 mol/L） while spike and flower shaped particles were formed for higher concentration. Photoluminescence characteristic band was observed with no shift at 390 nm indicating the stable nature of AgNPs. The antibacterial property of the AgNPs was tested against gram negative bacteria Pseudomonas aeruginosa by using Cissus quadrangular as a control and the result showed that vitamin C reduced AgNPs have good antibacterial activity.

Accelerated precipitation behavior of cast Mg-Al-Zn alloy by grain refinement

This study demonstrates that the precipitation behavior of 13-Mg17Al12 phase during aging and the resultant variation in hardness and mechanical properties of cast Mg-Al-Zn alloy are strongly dependent on initial grain size. Grain size reduction accelerates discontinuous precipitation at the early stage of aging treatment by increasing the area fraction of grain boundaries that can act as nucleation sites for discontinuous precipitates （DP）, but it does not influence DP growth rate. Grain refinement also prematurely terminates continuous precipitation because the formation of a large number of DP reduces the amount of AI dissolved in the matrix, which is required for the formation of continuous precipitates （CP）. This promotion of DP formation and early termination of CP formation significantly decrease the peak-aging time to one-third. The enhanced precipitation behavior also leads to an additional hardness improvement in the aged alloy, along with an increase in hardness owing to grain boundary strengthening by grain refinement. The amount of increase in hardness changes with aging time, which is determined by the variation of three variables with aging time： DP fraction difference between refined and nonrefined alloys, hardness difference between DP and matrix, and matrix hardness difference between the two alloys. Grain refinement improves both tensile strength and ductility of the homogenized alloy owing to grain boundary strengthening and suppression of twinning activation, respectively. However, the loss of ductility after peak-aging treatment is greater in the refined alloy because of the larger amount of DP acting as a crack source in this alloy.