A review on ignition mechanisms and characteristics of magnesium alloys

Magnesium alloys have become more attractive because of their low density and electromagnetic shielding effectiveness in the aerospace industry.However,some unpredictable situation may lead to the ignition of magnesium alloys.In this review,the thermodynamic conditions and transfer processes of magnesium alloys ignition are analyzed from the point of mechanisms.The criteria of ignition are emphasized.In addition,ignitability and flammability test systems are compared.And a more suitable method to assess the potential ignition and flammability risks of magnesium alloys in extreme environments is recommended.Furthermore,the ignition characteristics of magnesium alloys are discussed in detail.It was found that the ignition of magnesium alloys is a complex process determined by internal properties such as thermo-physical properties,oxide film properties,chemical compositions and geometrical parameters,as well as the external environment such as gas species,oxygen concentration and oxygen pressure.Ignition temperature is not physical constants of materials.It is not simply assumed that ignition may occur when the temperature of Mg alloys reaches a certain ignition point.Finally,the unsolved issues in the ignition of magnesium alloys are pointed out and the future investigation are suggested for improving the safety and reliability of magnesium alloys in the aerospace applications.

Characterization of microstructure evolution and mechanical properties of the spray-deposited AZ31 magnesium alloy

The cylindrical billets of a Mg-3Al-1Zn （AZ31） alloy were synthesized by spray deposition processing. The microstructure evolution and mechanical properties of the alloy were investigated. The results reveal that the microstructure of the AZ31 alloy is refined significantly by spray deposition processing. A homogeneous and equiaxial-grain structure with an average grain size of 17 μm is obtained. Further grain refinement with an average grain size of 5 μm is attributed to dynamic recrystallization during extrusion processing. The great increase in the density of grain boundary nucleation sites by the finer initial grain sizes makes the dislocation pile-ups near subgrain boundaries being absorbed easily by the boundaries, resulting in an accelerated recrystallization process. The average tensile ultimate and yield strengths of the extruded rods are 321 MPa and 237 MPa, respectively, with an elongation of 15.2% at room temperature, which are remarkably higher than those of the conventional as-cast AZ31 alloy.

Alpha-helical cationic antimicrobial peptides: relationships of structure and function

Antimicrobial peptides(AMPs),with their extraordinary properties,such as broad-spectrum activity,rapid action and difficult development of resistance,have become promising molecules as new antibiotics.Despite their various mechanisms of action,the interaction of AMPs with the bacterial cell membrane is the key step for their mode of action.Moreover,it is generally accepted that the membrane is the primary target of most AMPs,and the interaction between AMPs and eukaryotic cell membranes(causing toxicity to host cells)limits their clinical application.Therefore,researchers are engaged in reforming or de novo designing AMPs as a‘singleedged sword’that contains high antimicrobial activity yet low cytotoxicity against eukaryotic cells.To improve the antimicrobial activity of AMPs,the relationship between the structure and function of AMPs has been rigorously pursued.In this review,we focus on the current knowledge of α-helical cationic antimicrobial peptides,one of the most common types of AMPs in nature.