Mg-Al-Ca In-Situ Composites with a Refined Eutectic Structure and Their Compressive Properties

In a series of Mg _x (Al₂Ca)_100−x (76 ≤ x ≤ 87) ternary alloys near the Mg-(Mg,Al)₂Ca pseudo-binary eutectic point, different phases and morphologies based on ultrafine eutectic microstructure have been obtained by controlling the composition and changing the cooling rate via either induction melting or copper mold casting. For 81 ≤ x ≤ 87, the chill-cast alloys with ductile Mg dendrites embedded in an ultrafine [Mg + (Mg,Al)₂Ca] eutectic matrix exhibit gradually increased fracture strength from 415 to 491 MPa with the decrease of Mg content. At x = 79, the Mg₇₉Al₁₄Ca₇ alloy contains hard (Mg,Al)₂Ca precipitates coexisting with ductile Mg dendrite, dispersed in the strong eutectic matrix. This alloy exhibits the highest compressive fracture strength (600 MPa), and the specific strength reaches 3.4 × 10⁵ N·m·kg⁻¹. The alloys all exhibit substantial plastic strain (5 to 6 pct). The attainment of such a combination of strength and plasticity is an interesting and useful step in improving the mechanical properties of lightweight Mg alloys.