Mg-Al系合金半溶融成形加工材の引張特性に及ぼすAl量および熱処理の影響 Effects of aluminum content and heat treatment on tensile properties of semi-solid formed Mg-Al alloys
A semi-solid press-forming process was applied to Mg–4~8%Al, Mg–4~8%Al–2%Ca and Mg–4~8%Al–l%Si– 0.5%Ca alloys for a purpose of toughness improvement. Effects of heat treatment were investigated on tensile properties and microstructure of the semi-solid formings. Fine globular particles of the α-phace are distributed uniformely together with the fine eutectic constituent in the semi-solid formings made from 15% strained materials. The grain size of the α-phase particles in as-formed specimens decreases with increasing aluminum and calcium contents. A network of intermetallic compound, Mg<sub>17</sub>Al<sub>12</sub> crystallized along grain boundaries in the Mg–Al binary and Mg–Al–1%Si–0.5% Ca alloys, breaks up with decreasing aluminum content, resulting in increases both of tensile strength and of elongation. The Mg<sub>17</sub>Al<sub>12</sub> compounds disappear after the T4–treatment in the all investigated alloys, while the shape of Al<sub>2</sub>Ca compounds becomes globular after the T4–treatment of Mg–Al–2%Ca alloys alone. The microstructural changes clearly improve tensile strength and elongation. The age hardning by precipitation of Mg<sub>17</sub>Al<sub>12</sub> phase occurs by T6–treatment in the Mg–Al binary and Mg–Al–1%Si–0.5%Ca alloys with aluminum content more than 6%, and in the Mg– Al–2%Ca alloys with aluminum larger than 8%. The aged specimens exhibit higher tensile strength and 0.2% proof stress than as-formed spesimens.
軽金属 47(12), 672-678, 1997-12-30
The Japan Institute of Light Metals