Effects of Carbon and/or Alkaline Earth Elements on Grain Refinement and Tensile Strength of AZ31 Alloy

Abstract

The effects of carbon and/or alkaline earth elements Ca and Sr on the grain refinement and tensile properties of the AZ31 alloy have been investigated in the present study. A significant grain refining efficiency could be obtained for the AZ31 alloy modified by carbon inoculation and the grain refining efficiency could be further improved by the combination of 0.2 mass%C and alkaline earth elements of 0.2 mass%Ca or 0.2 mass%Sr. Compared to the AZ31 alloy without any treatment, the tensile properties of the AZ31 alloy were remarkably improved after being modified by the combination of carbon and a little addition of alkaline earth elements. The ultimate tensile strength and elongation to failure were improved by about 20% and 40%, respectively. After being refined either by 0.2 mass%C or by the combination of 0.2 mass%C and a little addition of alkaline earth elements (0.2 mass%Ca or 0.2 mass%Sr), the main fracture mechanism was changed from cleavage mode with large cleavage planes for the unrefined AZ31 alloy to mixed mode of cleavage and quasi-cleavage fracture. The fracture surfaces were almost composed of small cleavage planes with thin river patterns and quasi-cleavage planes with small dimples and severe plastic deformation.

Effects of Fe addition and addition sequence on carbon inoculation of Mg–3%Al alloy

“…For the refining mechanism of carbon inoculation, the hypothesis that Al 4 C 3 particles formed by reaction between Al and C in the Mg-Al melt should act as nucleating substrates for Mg grains has been widely accepted by many researchers [5][6][7][8][9][10][12][13][14][15][16][17][18]. However, it should be noted that the Al-C-O particles have been always found in the Mg-Al alloys inoculated by carbon [5,6,12,13,[16][17][18]. Likewise, the Al-C-O particles were also observed in the present study, as shown in Figs.…”

“…The refining mechanism of the carbon inoculation firstly proposed by Emley in his book [20] is that the Al 4 C 3 particles formed in the Mg-Al melt act as nucleating substrates for Mg grains during solidification. This hypothesis has been widely appreciated to date by many researchers [5][6][7][8][9][10][12][13][14][15][16][17][18].…”

“…Among a broad range of magnesium alloys, Mg-Al type alloys take a dominant position in the magnesium products [1][2][3]. The grain refinement has been proved to be a very effective route to improve the mechanical properties of the Mg-Al type alloys [4][5][6]. Many grain refining methods have been developed, such as addition of solute elements [4,7,8], superheating [7][8][9][10], FeCl 3 inoculation [11] and carbon inoculation [5][6][7][8][12][13][14][15][16][17][18][19].…”

Thermal stability of Al2MgC2 and thermodynamic modeling of the Al–C–Mg system - Application to grain refinement of Mg–Al alloys

“…This has been an active research topic for the last 20 years as this technique was proven to be the most promising alternative to the use of Zr which forms intermetallics with Al. Remarkable improvements of strength and ductility [12][13][14][15], creep resistance [16], corrosion resistance [17] and even hot working processing [18,19] of Mg-Al alloys were obtained by refining their microstructure. However, underlying mechanisms of the refinement has been widely disputed in the literature.…”

“…In addition, the duplex nucleation theory was contested by experimental evidence from Wang et al [28]. Finally, the Al4C3 carbide was widely considered to be the nucleant responsible for the refinement [13,15,[24][25][26][27][28][29][30][31]]. Yet recently, Huang et al [32] investigated Mg-Al alloys inoculated by SiC and characterized by TEM the presence of Al2MgC2 existing in a crystallographic orientation relationship with the α-Mg matrix.…”