Abstract: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 a-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 a-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.

Key words: Mg-Al alloy; iron; calcium; carbon inoculation; nucleating substrate; poisoning-free effect