Grain refinement of AZ91D magnesium alloy by MgCO3

Abstract

The grain refining technique of AZ91D magnesium alloy by MgCO 3 has been investigated. The refining mechanism and tensile properties of the resulting alloy have also been discussed. The results indicate that MgCO 3 can decrease its grain size from 311 to 53μm. Correspondingly, the tensile properties are obviously improved. The higher the cooling rate from addition temperature to pouring temperature or the higher the addition temperature, the finer the grains. The melt treated by MgCO 3 should be poured as soon as possible because the inoculation fading is quite quick. The microstructure sensitivity to the diameter of a cast rod is relatively high and the microstructures of the rods with large diameters are quite inhomogeneous. The refining mechanism of MgCO 3 belongs to heterogeneous nucleation and the nucleant substrates are believed to be the Al 4 C 3 particles formed from the reactions between the MgCO 3 and the molten alloy.

Inoculant Fading-Resistance of Fe-Bearing Mg–3%Al Alloys Refined by Carbon Combining with Calcium Addition

“…2935) In the previous researches performed by Chen et al, the grain sizes increased significantly with the extension of holding time for the AZ91 alloy inoculated by MgCO 3 and SiC, i.e., obvious inoculant fading phenomenon was observed. 36,37) They believed that the number of effective nucleant substrates was decreased when the holding time was extended. However, no evidence was provided in their studies.…”

Investigation on the Duration of Action of Mg3N2 as a Grain Refiner for AZ80 Alloy

“…The effect of a higher Al content in the AZ80 alloy on the grain size cannot be ruled out. When compared with the AZ91 alloy, the obtained grain size (146.3 ± 10.3 µm) in the AZ80 alloy is larger than the measured grain size (53 µm) with the addition of 1.0 wt.% MgCO 3 into AZ91D [6], which can be also attributed to the different Al content (solute effect of Al) and different nucleants. It should also be noted here that the melt treated by MgCO 3 should be poured as soon as possible because the inoculation fading is quite quick.…”

“…However, the grain refinement approach with zirconium [4], which is commonly used for non-Al-containing Mg alloys, does not work for this AZ Metals 2024, 14, 485 2 of 11 alloy family due to the formation of an AlZr intermetallic phase, which is ineffective for the grain refinement of Mg alloys [1]. Other grain refinement methodologies (i.e., rapid cooling, melt superheating, carbon inoculation [5][6][7], the addition of Al-Ti-C [8], B [9], Al-V-B master alloy [10], CaO [11], MgO [12,13], SiC [14], VN [15], Mg 3 N 2 [16][17][18], AlN [19], TiB 2 [20], Ca [21], the application of ultrasonic treatment [22]) have therefore been widely investigated, with a focus on the effect of particles on the grain restriction factor [23][24][25][26] and dendritic grain growth [27] as well as phase growth [28,29]. However, rapid cooling may not be a viable option for particular castings, while superheating uses extra energy and increases the oxidation of the melt.…”

Grain Refinement OfAZ91MgCasAlloy (Review Paper)

“…Also, investigated by HuiHan [38] And the grain refinement mechanism is attributed to Al4C3 can act as the efficiently heterogeneous nuclei of primary α-Mg and decrease the degree of undercooling the primary α-Mg phase. And another study by TiJun Chen [39], indicates that MgCo3 can decrease its grain size from 311 to 53 µm. Correspondingly, the tensile properties are improved.…”