Characterization of the Grain Structures in Vacuum-Assist High-Pressure Die Casting AM60B Alloy

doi:10.1007/s40195-016-0430-1

Abstract

Abstract:

The structures in vacuum-assist high-pressure die casting (HPDC) AM60B alloy were studied by using an optical microscope and a scanning electron microscope with an energy dispersive spectrometer. It was found that the HPDC under the vacuum could significantly change the morphology and distribution of the microstructure. For both conventional and vacuum-assist HPDC processes, the externally solidified crystals (ESCs) tended to aggregate in the center along the thickness direction of the castings. Besides, the aggregation was more pronounced, and the number of ESCs decreased, and the ESCs tended to become smaller and more globular, as the distance between the specimen location and runner increased. Compared with the conventional castings, the vacuum-assist HPDC can significantly reduce the size and amount of ESCs, and the ESCs tended to be more globular. For the distribution of ESCs along the thickness of the specimens, the aggregation tendency was more pronounced in vacuum-assist die castings than that in conventional castings. Besides, the distribution of ESCs at different locations was more converged in the vacuum-assist HPDC than that in the conventional HPDC.

Key words: AM60B alloy, Grain structure, Vacuum-assist high-pressure die casting, Externally solidified crystals

Xiao-Bo Li, Shou-Mei Xiong, Zhi-Peng Guo. Characterization of the Grain Structures in Vacuum-Assist High-Pressure Die Casting AM60B Alloy[J]. Acta Metallurgica Sinica (English Letters), 2016, 29(7): 619-628.

Figures/Tables 14

Fig. 1 Configuration of the “crash box” casting. The samples for microstructure analysis were extracted at locations A, B1, B2, and C, the microstructure observation area of location B1 (also the locations A, B2, and C) was shown in the upper right corner. The interfacial heat transfer analysis was conducted at locations TA and TB

Table 1 Key parameters adopted during conventional and vacuum-assist HPDC processes

Pouring temperature (°C)	Initial mold temperature (°C)	Casting pressure (MPa)	Slow shot velocity (m/s)	Fast shot velocity (m/s)
680	180	87	0.2	2.5

Table 2 Chemical compositions of the AM60B magnesium alloy used in the study (mass%)

Al	Mn	Zn	Si	Cu	Fe	Mg
5.9	0.31	0.16	0.06	0.007	0.003	Bal

Fig. 2 A typical microstructure at location A of the conventional HPDC crash box (P1, P2, and P3 were marked as the locations where the EDS analysis was performed)

Table 3 Quantity of elements according to EDS analysis (mass%)

Position	P₁	P₂	P₃	ESCs	α-Mg grains	Eutectic
Mg	98.04	95.48	79.70	97.76-100	95.61-92.50	68.96-82.34
Al	1.96	4.52	20.30	0-2.24	4.39-7.50	17.66-27.71
Mn	0	0	0	0	0	0-3.34

Fig. 3 Comparison of the microstructures between the surface layer (top row) and the center (bottom row) at location A of the conventional HPDC crash box: a, c OM, b, d SEM

Fig. 4 Comparison of the microstructures between the surface layer (top tow) and the center (bottom row) of the conventional HPDC crash box. From left to right, each column of the figures shows the microstructures at locations A, B1, B2, and C (see Fig. 1), respectively

Fig. 5 Comparison of the microstructures at location A of the conventional (top row) and vacuum-assist (bottom row) HPDC crash boxes: a, d the microstructures in the surface layer, b, c, e, f the microstructures in the center of the samples

Fig. 6 Comparison of a the area fraction, b average diameter of ESCs at different locations of the conventional and vacuum-assist HPDC crash boxes

Fig. 7 Comparison of a the peak values of IHTC, b the melt surface temperature under conventional and vacuum-assist HPDC processes

Fig. 8 Comparison of the microstructure of the cross section at different locations. From left to right, each column of images correspond to locations A, B1, B2, and C of conventional (top row) and vacuum-assist (bottom row) HPDC crash boxes

Fig. 9 Comparison of the aggregation tendency, d at different locations of the conventional and vacuum-assist HPDC crash boxes

Fig. 10 Relative area friction and number fraction of ESCs as a function of the ESC diameter at the location A of the conventional and vacuum-assist HPDC crash boxes

Fig. 11 Area fraction of ESCs as a function of the normalized thickness at different locations of a conventional, b vacuum-assist HPDC crash boxes

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