Effect Of Mischmetal And Ca On The Microstructures And Mechanical Properties Of AZ91 Alloys

As the lightest constructional material, Mg alloy has high specific strength, high specific stiffness, good magnetic-shielding ability, good damping ability, and good mechanical property. Since its chemical character is very active, Mg alloy is prone to oxidation and burning, which makes it impossible to be melted and cast in air. Oxidation and burning of Mg alloy obstruct its application greatly. Fluxes and cover gases are currently used for the melting and production processes, and semi-solid thixocasting is also used to lower the operation temperature; but there still remain many problems. Alloying is a kind of promising method of preventing Mg alloy from burning. â‘ Alloying is used here to prevent Mg alloy from oxidation. The widely used Mg alloy AZ91 is chose as the original alloy. On the surface of the molten alloy, a layer of protective film with dense structure is formed by the addition of mischmetal. The film prevents the penetration of oxygen and volatilization of Mg vapor, and then prevents the AZ91 alloy from oxidation and burning.During the experiments, the effects of self-made mischmetal additions on the ignition temperature of AZ91D Mg alloy are investigated. The mechanism of ignition-proof and the effects on mechanical properties are investigated. It is shown, for AZ91D with mischmetal in the range of 0.08% to 0.12%, that the ignition temperature point can be greatly heightened, that the quality of oxide film is obviously improved, that the as-cast microstructure is refined greatly, and that the mechanical property is bettered a little. â‘¡Otherwise, the regeneration power of the oxide film and the proof-ignition reappearance of re-melting alloy were elementarily researched. It is found that when the alloy is in fluxion oxide film is formed quickly and cover the surface, so the regeneration power is satisfying, and that the ignition temperature of re-melting alloy, oxide film and the mechanical property do not change evidently. â‘¢Lately, other researchers also add pure Ce, mischmetal with rich Ce in AZ91D Mg alloy to heighten the ignition temperature, but because the element and the ratio among elements is different the result is very different. In our experiments, the less quantity was added, and the higher ignition temperature was got. When the highest ignition temperature is reached the quantity of self-made mischmetal is only 0.1%.Study on ignition-proof Mg alloy with mischmetal offers a kind of new ignition-proof Mg alloy that is fit to current production process, at the same time that it also offers broad field for application of the abundant rare earth resources in China.