Study On The Preparation And Semi-solid Of Ignition-proof Magnesium Alloy

As the lightest metal structure material, Mg alloy was widely used, because of its high specific strength, high specific stiffness, good magnetic-shielding ability, good damping ability, and good mechanical property. However, Mg alloy is prone to oxidation and burning at elevated temperature, which obstruct its application greatly. Alloying is a kind of promising method of preventing Mg alloy from burning. The development of semi-solid technology provided wider prospect for Mg alloy.Kinetics condition and thermodynamic condition of Mg alloy oxidation were analyzed by studying the oxidation phenomenon of Mg alloy at elevated temperature. The results showed that, realization of alloying ignition-proof must satisfy kinetics condition and thermodynamic condition :①Eqvationin reacted the oxide of alloying element must be in positive direction, and density of oxideηmust be more than 1 .②It must satisfy diffusion condition to possess enough foregoing oxide of alloying element in oxidized films every time. Ignition proof AZ61-1.0%Y with good fire retardant effects and mechanical properties was prepared by adding 1%Y into AZ61. Proper Y content had obvious fire retardant effects on AZ61, fined microstructure of Mg alloy and proved mechanical properties. Nevertheless, Mg alloy grain went coarse and mechanical properties decreased with excess Y.The semi-solid ignition proof AZ61-1.0%Y slurry which was prepared by the self-made mechanical stirring equipment was fine, round and uniformly distributed. The effect of process parameters (stirring temperature, stirring speed, stirring time and cooling rate) on the semisolid structure of AZ61-1.0%Y was studied. It has been found that the optimum process technology was stirring with the speed of 500 r/min at below 605℃. Research on the formation mechanism about semisolid structure of Mg alloy during the string condition was favorable for semisolid technology.An investigation that fairly ideal semisolid globular structure at various holding temperature and time by reheating ignition-proof Mg alloy AZ61-1.0%Y using man designed remelting furnace was beneficial to the development of semisolid reheating. Results of the experiment show that proper semi-solid remelting temperatures of the alloy is in the range of 580℃-600℃. The higher isothermal treatment temperature, the quicker spheroidizing speed of primaryα-Mg. If isothermal treatment temperature is too low or isothermal treatment time is too short, ignition-proof Mg alloy AZ61-1.0%Y will cannot spheroidizing.Contrarily,if isothermal treatment temperature is too high or isothermal treatment time is too long, the globular structure of primaryα-Mg will become coarse,agglomeration,melting.On macroscopical,its strength is not enough, collapse,even fluid loss,making the next step thixoforming cannot be done. The microstructural evolution of the reheated semisolid alloy formation might consist of three stages:①eutectic structure melting.②α-grain spheroidizing.③theoretical liquid-solid equilibrium.