ABSTRACT
In this study, commercial AZ31B magnesium alloy was used to compare the differences between the microstructure, texture, and mechanical properties of conventional solidification (as homogenized AZ31) and rapid solidification (as RS AZ31). The results demonstrate that a rapidly solidified microstructure leads to better performance after hot extrusion with a medium extrusion rate (6 m/min) and extrusion temperature (250 °C). The average grain size of as-homogenized AZ31 extruded rod is 100 µm after annealing and 4.6 µm after extrusion, respectively, but that of the as-RS AZ31 extruded rod is only about 5 µm and 1.1 µm, correspondingly. The as-RS AZ31 extruded rod attains a high average yield strength of 289.6 MPa, which is superior to the as-homogenized AZ31 extruded rod, and is improved by 81.3% in comparison. The as-RS AZ31 extruded rod shows a more random crystallographic orientation and has an unconventional weak texture component in <112¯1>/<202¯1> direction, which has not been reported yet, while the as-homogenized AZ31 extruded rod has an expected texture with prismatic <101¯0>/<1¯21¯0>//ED.
ABSTRACT
ZK60 alloy metal ribbons were prepared successfully in a carbon dioxide atmosphere by varying the speeds of melt spinning. The thin metal ribbon with different solidification speeds was prepared by controlling different rotation speeds, and the influence of solidification speed on the ZK60 ribbon was studied. The results show that the gas mark has a significant effect on the local structure of the ribbon. The gas mark's proportional area of the ZK60 ribbon increases first and then decreases with the increase in roll speed, and the gas mark proportion area is the smallest at 17.6 m/s. With the increase in the solidification rate, the base texture of the ribbon is enhanced, and the proportion of columnar crystals in the ribbon gradually increases. At the rate of 17.6 m/s, columnar crystals run through the entire side of the ribbon, and uniformly distributed spherical-particle phases are found inside the grain. At the speed of 17.6 m/s, the mechanical properties of different areas of the ribbon are close and different from those of the other two speeds, and the performance of the quenching zone is better than that of the slow-cooling zone.
ABSTRACT
Inoculation of a food product for use in subsequent validation studies typically makes use of a high concentration cocktail of microorganisms suspended in aqueous media. However, this inoculation method may prove difficult particularly when the food product is a low-moisture food containing antimicrobial compounds, such as some dried spices. In this study, a dry transfer method for inoculation of clove powder, oregano leaves, ginger powder, and ground black pepper with a five-serovar cocktail of Salmonella was developed and compared with a traditional aqueous inoculation procedure. Spices were inoculated at three levels, 10, 8, and 6 log CFU/g, by using both an aqueous suspension of Salmonella and a dry transfer of Salmonella from previously inoculated silica beads. At the highest inoculation level, the dry transfer method resulted in a significantly higher microbial load (P < 0.05) for ground cloves and oregano, but not for ginger and ground black pepper. At the intermediate inoculation level, differences were apparent only for ginger and black pepper. Inoculation levels of 6 log CFU/g resulted in recoveries below detection limits for both methods of inoculation. Additional examination on the survival of Salmonella on silica beads after inoculation and in clove powder after dry transfer from silica beads showed linear rates of decline, with a rate of -0.011 log CFU/g/day for beads and -0.015 log CFU/g/day for clove powder. The results suggest that dry transfer of Salmonella via inoculated silica beads is a viable alternative when traditional aqueous inoculation is not feasible.
