AZ61鋳造材の熱間加工性に及ぼす熱処理とCa添加の影響

概要

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Recently magnesium alloys sheets have been widely applied to the chassis of electronics appliances such as laptop PCs, cellular phones, digital cameras. So far AZ31(Mg-3 mass%Al-1 mass%Zn) with relatively good hot-workability has been used for the material of such applications. On the other hand higher strength sheets are strongly required because high rigidity and stiffness are necessary to the chassis with smaller form factors. In this study the effect of heat treatment and small amount of calcium addition up to 0.03 mass% on the hot-workability of cast AZ61(Mg-6 mass%Al-1 mass%Zn) alloy was investigated. Although AZ61 has poor hot-workability in the as-cast condition, it drastically improves by heat treatment at 673 K for 360 ks because of the dissolution of β-Mg17Al12 phase that becomes the origin of crack. Heat treated AZ61 with small amount of calcium addition has better hot-workability than that without calcium addition. That is due to the suppression of grain growth in the heat treatment by existing calcium bearing inclusions as small particles with pinning effect. The hot workability of AZ61 with 0.01 mass% calcium is as good as that of AZ31, a conventional magnesium alloy for hot rolling.