Magnesium alloys formed by adding various elements to magnesium have so far been used for housing cases of portable electrical devices, such as a cellular mobile telephone and a notebook-type personal computer, parts of automobiles, and so on. Because a magnesium alloy has a hexagonal-crystal structure (a hexagonal close-packed (hcp) structure), it has poor plastic processibility at the ordinary temperature. Consequently, the above-described magnesium alloy products such as the housing cases are mainly produced by using a cast material formed through the die-casting process or thixomold process.
To improve the plastic processibility of the magnesium alloy, Patent Literature 1 has proposed to disperse a plurality of precipitated substances in the crystal grain of the magnesium alloy, the precipitated substances each having an area of 25×10−12 π m2 or more and 2,500×10−12 π m2 or less (the diameter of the circle having the same area: 10 to 100 μm). Patent Literature 2 has disclosed that the plastic processibility (formability) becomes excellent when the crystalline precipitated substance in the magnesium alloy is fine-grained such that it has a maximum diameter of 20 μm or less.
Patent Literature 1: the published Japanese patent application Tokukai 2003-239033
Patent Literature 2: the internationally published pamphlet 06/003899