Oxidation Behavior of the Feedstock
An extremely high affinity of magnesium to oxygen, along with the highly developed surface area of magnesium alloy chips, used as a feedstock during injection molding, makes the system prone to oxidation. It is anticipated that alloy protection inside the machine barrel by an inert atmosphere of argon is essentially better than molten surface shielding by SF6 gas during die casting. So far there is a lack of experimental verification, and existing data send a rather unclear message. First, the inertness of an argon atmosphere is sensitive to small amounts of entrapped air, and the growth rate of MgO on Al-based alloy at temperatures of 450 °C to 800 °C in a mixture of Ar+1%O2 and Ar+5%O2 equals 25% and 70%, respectively, of the oxidation rate in air . Second, the final oxygen content in molded parts is still about one order of magnitude higher than that present in an initial feedstock . A description of the alloy oxidation behavior is therefore of key importance for designing material feeding and Ar flow systems. It is also important for feedstock manufacturing in terms of morphology and its chemical modification against oxidation. In particular, it is helpful in verifying the necessity of beryllium additions routinely used in conventionally cast alloys.
KeywordsMagnesium Alloy Injection Molding Ignition Temperature AZ91D Alloy AZ91D Magnesium Alloy
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