Poisoning-free effect of calcium on grain refinement of Mg–3%Al alloy containing trace Fe by carbon inoculation

Mg-3%Al alloy was modified by combining Ca addition with carbon inoculation. The effects of Fe addition and addition sequence on the grain refinement were investigated. A higher grain refining efficiency could be obtained for the Mg–Al alloy modified by combining Ca addition with carbon inoculation. Fe addition and addition sequence had no obvious effect on the grain refinement. Ca addition could effectively avoid grain-coarsening resulting from Fe in the carbon-inoculated Mg–Al alloy. The Al-C-O particles, actually being Al4C3, should act as potent substrates for α-Mg grains in the sample treated by combining Ca addition with carbon inoculation. However, the duplex-phase particles of Al4C3 coated on Al-Fe or Al-C-Fe should be the potent substrates for α-Mg grains if Fe existed in the Mg–Al melt. Ca addition can contribute to the formation of the particles of Al4C3 coated on Al-Fe or Al-C-Fe, regardless of the Fe addition sequence. The poisoning effect of Fe was effectively inhibited in the carbon-inoculated of Mg-Al alloy due to Ca addition, namely, Ca has a poisoning-free effect.