Investigation On Ignition And Combustion Characteristics Of Al-mg Alloy

Metal aluminum is widely used in the field of energetic materials owe to its low oxygen consumption,high energy density and low cost.Since the 1970 s,many researchers at home and abroad have carried out a lot of research on the oxidation mechanism,ignition and combustion characteristics of aluminum.Many proposals have been made for the disadvantages of micro-aluminum combustion,such as slag accumulation and long ignition delay time,but still not completely solved.From the point of view of binary alloys,another metal with a large difference in boiling point is added to the metal aluminum to form an alloy system,which weakens the sintering behavior of aluminum by boiling and micro-explosion in the ignition and combustion process.And shorten the ignition delay time of aluminum.Through screening,this paper selects aluminum-magnesium alloy as the research system,builds laser ignition and combustion test platform,tests single aluminum and aluminum-magnesium alloy fuel and powder fuel,and compares the difference of ignition and combustion performance between aluminum and aluminum-magnesium alloy.Therefore,this research is of great significance for improving the ignition and combustion properties of aluminum and revealing the combustion mechanism of aluminum-magnesium alloy,which lays a foundation for further promoting the practical application of aluminum.In this paper,we first built a micro-high-speed imaging experimental setup and corresponding measurement system,which can clearly record the physical shape changes(such as particle shape,particle size,etc.),ignition characteristics,flame characteristics of the micron-sized individual particle during ignition and combustion.Then analyze the ignition delay time,flame propagation rate,flame front change and other information,combined with theoretical analysis to obtain its associated ignition and combustion mechanism.The physical and thermal properties of aluminum and aluminum-magnesium alloys were then characterized by TEM,SEM,XRD,TG and other methods.Finally,the laser ignition and combustion characteristics of individual micron aluminum,individual micro-aluminum-magnesium alloy and aluminum-magnesium alloy powders in air were studied.The results show that micron aluminum is subjected to four stages after being heated by laser: The particles are thermally expanded;the alumina shell is broken,the molten aluminum core overflows;the aluminum shell melts,the aluminum evaporates and ignites;the aluminum vapor burns.The combustion of Al-Mg alloy particles is mainly the sequential combustion of magnesium component and aluminum component.The combustion intensity of aluminum component is obviously stronger than that of magnesium component;the laser heating power has great influence on ignition performance.As the laser power density is increased,the temperature rise rate increases,and the ignition delay time is shortened,the ignition probability is increased.On the other way,the probability of the micro-explosive behavior occurs continuously in the combustion process,and the single and multiple agglomerated alloys undergo multiple micro-explosions,and dispersive boiling before the micro-explosion increases.The summary analysis shows that the combustion process of aluminummagnesium alloy can be divided into four stages: initial oxidation stage(the degree of oxidation of the particles becomes larger,oxidation occurs near the surface of the particles);magnesium combustion stage(Magnesium melts and spreads out,mixing with oxygen for the first ignition);the transition stage(the end of the first stage of combustion,the heat released by the combustion and laser,heating the remain particles together,the porous structure occurs inside the particles);the combustion stage of the aluminum(the flame occurs from the surface of the particles,gradually diffusion inward until the entire particle is wrapped,the flame is spherical and uniform.As the particles burn,the size of the combustion zone decreases until quenching).