A new Al-Zr-Ti master alloy for ultrasonic grain refinement of wrought and foundry aluminum alloys

A new grain refiner master alloy based on the Al-Zr-Ti system was prepared by salt assisted synthesis. 90% of Al3Zr particles in the master alloy were ranged between 1 and 13 μm. 80% reduction of grain size was observed with the addition of 0.2wt% Zr equivalent master alloy combined with ultrasonic treatment in an Al alloy. The new master alloy demonstrated 30% improvement in grain refinement efficiency compared to the one prepared by a conventional alloy route.The authors wish to acknowledge financial support from the ExoMet Project, which is co-funded by the European Commission in the 7th Framework Programme (contract FP7-NMP3-LA-2012-280421), by the European Space Agency and by the individual partner organisations

Microstructural evolution in solution heat treatment of gas- atomised Al alloy (7075) powder for cold spray

Cold gas dynamic spray is being explored as a repair technique for high-value metallic components, given its potential to produce pore and oxide-free deposits of between several micrometers and several millimeters thick with good levels of adhesion and mechanical strength. However, feedstock powders for cold spray experience rapid solidification if manufactured by gas atomization and hence can exhibit non-equilibrium microstructures and localized segregation of alloying elements. Here, we used sealed quartz tube solution heat treatment of a precipitation hardenable 7075 aluminum alloy feedstock to yield a consistent and homogeneous powder phase composition and microstructure prior to cold spraying, aiming for a more controllable heat treatment response of the cold spray deposits. It was shown that the dendritic microstructure and solute segregation in the gas-atomized powders were altered, such that the heat-treated powder exhibits a homogeneous distribution of solute atoms. Micro-indentation testing revealed that the heat-treated powder exhibited a mean hardness decrease of nearly 25% compared to the as received powder. Deformation of the powder particles was enhanced by heat treatment, resulting in an improved coating with higher thickness (* 300 lm compared to * 40 um for untreated feedstock). Improved particle–substrate bonding was evidenced by formation of jets at the particle boundaries

Grain refinement of Al-Si hypoeutectic alloys by Al3Ti1B master alloy and ultrasonic treatment

Al-Si alloys are widely used in automotive and aerospace industries due to their excellent castability, high strength to weight ratio and good corrosion resistance. However, Si poisoning severely limits the degree of grain refinement with the grain size becoming larger as the Si content increases. Generally the effect of Si poisoning is reduced by increasing the amount of master alloy added to the melt during casting. However, an alternative approach is physical grain refinement through the application of an external force (e.g. mechanical or electromagnetic stirring, intensive shearing and ultrasonic irradiation). This work compares the grain refining efficiency of three approaches to the grain refinement of a range of hypoeutectic Al-Si alloys by (i) the addition of Al3Ti1B master alloy, (ii) the application of Ultrasonic Treatment (UT) and (iii) the combined addition of A13Ti1B master alloy and the application of UT

Tailored ß-Cyclodextrin Blocks the Translocation Pores of Binary Exotoxins from C. Botulinum and C. Perfringens and Protects Cells from Intoxication

International audienceBackgroundClostridium botulinum C2 toxin and Clostridium perfringens iota toxin are binary exotoxins, which ADP-ribosylate actin in the cytosol of mammalian cells and thereby destroy the cytoskeleton. C2 and iota toxin consists of two individual proteins, an enzymatic active (A-) component and a separate receptor binding and translocation (B-) component. The latter forms a complex with the A-component on the surface of target cells and after receptor-mediated endocytosis, it mediates the translocation of the A-component from acidified endosomal vesicles into the cytosol. To this end, the B-components form heptameric pores in endosomal membranes, which serve as translocation channels for the A-components.Here we demonstrate that a 7-fold symmetrical positively charged ß-cyclodextrin derivative, per-6-S-(3-aminomethyl)benzylthio-ß-cyclodextrin, protects cultured cells from intoxication with C2 and iota toxins in a concentration-dependent manner starting at low micromolar concentrations. We discovered that the compound inhibited the pH-dependent membrane translocation of the A-components of both toxins in intact cells. Consistently, the compound strongly blocked transmembrane channels formed by the B-components of C2 and iota toxin in planar lipid bilayers in vitro. With C2 toxin, we consecutively ruled out all other possible inhibitory mechanisms showing that the compound did not interfere with the binding of the toxin to the cells or with the enzyme activity of the A-component.Conclusions/SignificanceThe described ß-cyclodextrin derivative was previously identified as one of the most potent inhibitors of the binary lethal toxin of Bacillus anthracis both in vitro and in vivo, implying that it might represent a broad-spectrum inhibitor of binary pore-forming exotoxins from pathogenic bacteria

AlSi5Mg0.3 Alloy for the Manufacture of Automotive Wheels

The heat-treated AlSi7Mg0.3 alloy is the standard wheel alloy as it offers the best compromise between fatigue strength and elongation. Alloys with less than 7 wt% Si may also be of interest for the manufacture of aluminium wheels to limit Si poisoning that impairs grain refinement. Hence, the potential of AlSi5Mg0.3 alloy was investigated as it could offer superior mechanical properties owing to a smaller grain structure. AlSi5Mg0.3 alloy does indeed exhibit smaller grains but fails to offer higher mechanical properties. AlSi7Mg0.3 alloy with a smaller dendritic structure but coarser grains is superior. The higher fluidity of the latter is believed to offer better feeding characteristics, which in turn improves the soundness of the casting and thus leads to superior structural quality and mechanical properties. An overall industrial assessment favours the standard Al7Si0.3 Mg alloy in the manufacture of light alloy wheels