Effect of Calcium on Oxidation Resistance and Fluidity of Magnesium ‎Alloy AZ91‎

Mg alloy is easily oxidized during melting in the unprotected atmosphere. This affects on the quality and cleanness of the alloy. In addition, the presence of oxide layer on the surface of melt decreases its fluidity so use of magnesium alloys in thin-film casting is faced with Serious limitation. In this paper, effect of adding calcium on the oxidation resistance and fluidity of AZ91 alloy melt have been investigated. For this purpose, samples of AZ91 alloy were prepared with different amounts of calcium. Afterward samples were stored at 700 ° C for different periods of time in furnace atmosphere .Microstructural, GI-XRD and surface oxidation tests showed that, a dense and compact oxide film composed of CaO is formed on surface, which performs melt protection and prevents penetrating of oxygen into the melt .As a result, the melt stables at a temperature of 700 ° C without presence of a protective gas .The most important advantage of use of calcium in magnesium alloys is not applying protective gases such as SF6. To investigate the fluidity of AZ91 alloy in the presence of calcium, the fluidity test was performed by using spiral pattern. The test results showed that by adding calcium, length of fluidity increased from about 100 mm to 340 mm.