Study On Combustion Of AZ Magnesium Alloy And Its Alloying With Ca And Gd

AZ magnesium alloys have been widely used in various industries due to their excellent mechanical properties,low density and relatively low cost.While their application is limited by flammability,low corrosion resistance,and poor plastic deformation.Therefore,the composition improvement of AZ magnesium alloys and the development of other new-type magnesium alloys are mainly aimed at solving the problems above.Due to the excellent lightweight effect of magnesium alloys,its application in aerospace,transportation and other fields has always been highly concerned,but the safety of aircrafts and vehicles has strict requirements on the flame retardancy of manufacturing materials.Due to the high activeness of magnesium,the flame retardancy of magnesium alloy components is an important consideration in their application.And,the existing research on the flammability of magnesium alloy and its composition adjustment mainly remains on the impact of the ignition point.There are few discussions about the combustion dynamics and the essential mechanism of the combustion.Therefore,the dynamic influencing factors and physical mechanism of magnesium alloy combustion are systematically studied,which has important theoretical and practical significance.This paper investigated the effect of Al content,heating rate and time of solid solution treatment on ignition temperature aiming at analyzing the flammability of AZ31,AZ61 and AZ80 alloys.In addition,AZ80 alloy was alloyed to investigate effect of Ca and Ca,Gd adding on ignition point,flame retardancy and oxidation behavior and its mechanism.Details are as follows:(1)The results show that the content of Al in AZ31,AZ61 and AZ80 influenced ignition temperature remarkably and with the addition of Al ignition temperatures decreased gradually.The content of Al in AZ magnesium alloys changed the solidification temperature range which influenced pyrolysis temperature and ignition temperature.And also the compactness of the oxide film on surface of the alloy before combustion was influenced by the content of Al.(2)Heating rate could also affect ignition temperature significantly,with the increase of heating rate,ignition point of magnesium alloys improved remarkably.The reason for increase of ignition temperature with increasing of heating rate is oxide film generated during fast heating rate is dense and uniform,delaying the rupture time and rupture temperature of oxide film accordingly.(3)The results of the study showed that the effect of the solution treatment on the ignition point of the magnesium alloy was not obvious,indicating that the magnesium alloy of a specific composition could not significantly improve its ignition point through solution treatment.This is mainly because sample without solid solution treatment will also experience a similar process of solid solution treatment,so when the temperature near the ignition point,there will be no significant difference between the two flammability.(4)The addition of Ca could significantly improve ignition temperature and oxidation resistance of AZ80 alloy,besides the more Ca content the higher ignition temperature and the better oxidation resistance.With the adding of Ca in AZ80,the divorced eutectic ?-Mg17Al12 and ?-Mg+?-Mg17Al12 intermetallic in a lamellar eutectic micro-constituent were replaced by chain-shaped phase and network structure which were considered as ?-Mg17Al12+(Mg,Al)2Ca eutectic micro-constituent uniformly scattered in ?-Mg matrix,and with the increase of Ca,the content of(Mg,Al)2Ca also increased correspondingly.After oxidized chain-shaped phase and network structure were fragmented and replaced by Al2Ca in spherical and rod like structures which was thermostable increasing the thermal stability of matrix and improved oxidation resistance.(5)The addition of Gd in AZ80-0.8Ca alloy reduced ignition point and oxidation resistance,and the more Gd adding the lower ignition temperature and worse oxidation resistance.New phase of Al2Gd and Al8Mn4Gd appeared and the chain-shaped and skeletal(Mg,Al)2Ca were no longer continuous but dispersed into broken dendritic shapes depending on the presence of Al2Gd.In addition,the size of Al2Gd and Al8Mn4Gd were biger and more island-like ?Mg17Al12 intermetallic appeared which was flammable and poor resistance to oxidation weakened flame retardant property and oxidation resistance of alloy.