Grain size distribution in a complex AM60 magnesium alloy die casting

Laukli, Hans Ivar; Lohne, O.; Sannes, Stian; Gjestland, Haavard; Arnberg, L.

doi:10.1080/13640461.2003.11819629

Cited by 46 publications

(28 citation statements)

References 5 publications

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“…For all the other compositions the surface regions contain increasingly smaller grains, whereas large grains continued to be observed at the core. For the more concentrated alloys, the coarse grains are known to form in the shot sleeve [4,20,21] and they will be termed externally solidified grains (ESG). For the purposes of this paper, the grains formed in the die cavity will be denoted internally solidified grains (ISG).…”

Section: Resultsmentioning

confidence: 99%

“…[4,15,19] This bimodal grain structure is thought to be formed through two main processes: [10,20,21] the small grains near the surface result from the fast solidification rate inherent to the hpdc process, and are thus related to the so-called 'skin effect'; [4,6,7,15,16,19] the large grains, sitting mainly at the core, are normally ascribed to the formation of crystals through partial solidification in the shot sleeve, which are injected into the die cavity during the casting. Depending on the casting geometry, other grain refining effects related to the melt flow inherent to the die casting process, and leading to grain shearing and fragmentation, may also take part in the generation of the grain structure.…”

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confidence: 99%

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Solute Content and the Grain Microstructure of High Pressure Diecast Magnesium–Aluminium Alloys

2009

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Seven binary alloys, with Al contents from 0.47 to 11.6 mass%, have been studied using electron back scattered diffraction. Grain size measurements were made at two opposing surface locations and at the core of the castings cross-sections. The alloy with 0.47 mass% Al showed a uniform microstructure of relatively large grains over the entire cross section, whereas higher Al content alloys showed an increasingly bimodal, non-uniform grain structure, with mostly fine grains near the surfaces and mixed fine and coarse grains at the core. The average grain size at the surfaces decreased for solute contents of up to 5.51 mass% Al. No further grain refining was observed for higher solute contents. The average size, d, of the surface grains was found to fit the relationship, d ¼ a þ b = Q , where Q is the growth restriction factor imposed by the solute and a and b are constants. The proportion of coarse grains at the core appeared to be related to the alloy's solidification range, and reached a maximum also for the alloy with 5.51 mass% Al. The degree of bimodality of the grain populations at the core and surface, portioned according to statistical techniques, was maximum for the alloy with 5.51 mass% Al.Despite the large amount of effort devoted to relate the tensile properties to the solidification structure of high pressure diecast (hpdc) magnesium (Mg) alloys, [1][2][3][4][5][6][7][8][9][10][11][12][13][14] little systematic work has been reported on how the grain microstructure is affected by the solute content. This is important for two reasons. One is whether grain nucleation and growth in hpdc is controlled by the solute concentration as in quiescent castings. The other refers to the non-uniformity of the grain structure which characterises hpdc. The small grain sizes near the surface of the castings are usually considered to dominate the strength [3,4,[6][7][8][14][15][16][17] through a strong Hall-Petch effect. However, as discussed thoroughly by Kurzydlowski and Bucki, [18] a mixture of grain sizes on the specimen cross-section may actually lead to an overall softening, and generally affect the flow behaviour. Therefore, an accurate description of the distribution of grain sizes over the casting's cross-section for different solute contents is necessary in order to both quantify the Hall-Petch contribution to the overall strengthening, and understand the way MgÀAl alloys yield plastically.The region near the surface of the casting cross-section normally contains a predominantly fine grain structure, while the centre, or 'core', includes a large fraction of coarse grains. [4,15,19] This bimodal grain structure is thought to be formed through two main processes: [10,20,21] the small grains near the surface result from the fast solidification rate inherent to the hpdc process, and are thus related to the so-called 'skin effect'; [4,6,7,15,16,19] the large grains, sitting mainly at the core, are normally ascribed to the formation of crystals through partial solidification in the shot sleeve, which are injected in...

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Solute Content and the Grain Microstructure of High Pressure Diecast Magnesium–Aluminium Alloys

2009

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“…Large dendritic grains form in the shot sleeve and they are then carried through the gate (where some are fragmented) into the die cavity while a second population of small equiaxed grains is formed in the die cavity and these comprise the majority of the structure. [3][4][5][6][7] The effect of this mixed distribution on the Hall-Petch relationship is crucial to an understanding of the yield strength and it is, therefore, important to measure the grain size distribution. Second, many authors have noted that magnesium high pressure die castings have a ''skin'', and some have claimed that it is characterised by an especially small grain size.…”

Section: Introductionmentioning

confidence: 99%

Grain Size Measurements in Mg-Al High Pressure Die Castings Using Electron Back-Scattered Diffraction (EBSD)

et al. 2004

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Optical metallographic techniques for grain-size measurement give unreliable results for high pressure diecast Mg-Al alloys and electron back-scattered diffraction mapping (EBSD) provides a good tool for improving the quality of these measurements. An application of EBSD mapping to this question is described, and data for some castings are presented. Ion-beam milling was needed to prepare suitable samples, and this technique is detailed. As is well-known for high pressure die castings, the grain size distribution comprises at least two populations. The mean grain size of the fine-grained population was similar in both AZ91 and AM60 and in two casting thicknesses (2 mm and 5 mm) and, contrary to previously published reports, it did not vary with depth below the surface.

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“…Meanwhile, the area fraction of the ESCs along the thickness of the die casting satisfies a Gaussian distribution, while its value at the central region may be up to 25%. Based on experimental studies [3,4], the percentage of the ESCs is higher at the area near the gate than that of far from the gate of the castings. Besides, the percentage of the ESCs increases when decreasing the pouring temperature and the slow shot phase plunger velocity.…”

Section: Morphology and Distribution Of The Escs And The Divorced Eutmentioning

confidence: 99%

“…One of the key microstructure characteristics of high pressure die cast magnesium alloy is the appearance of relatively coarse dendrites at the central region of castings. Based on experimental studies and numerical simulation of the filling sequence and solidification behaviour during the HPDC process [2][3][4], these coarse dendrites have been proven to originate from the nucleation and crystal growth in the melt in the shot sleeve, and they are named "Externally Solidified Crystals" or "ESCs" for short. The externally solidified crystals have a significant impact on the quality and performance of magnesium alloy die castings.…”

Section: Introductionmentioning

confidence: 99%

Modeling of microstructure evolution of magnesium alloy during the high pressure die casting process

Xiong

2012

IOP Conf. Ser.: Mater. Sci. Eng.

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Abstract. Two important microstructure characteristics of high pressure die cast magnesium alloy are the externally solidified crystals (ESCs) and the fully divorced eutectic which form at the filling stage of the shot sleeve and at the last stage of solidification in the die cavity, respectively. Both of them have a significant influence on the mechanical properties and performance of magnesium alloy die castings. In the present paper, a numerical model based on the cellular automaton (CA) method was developed to simulate the microstructure evolution of magnesium alloy during cold-chamber high pressure die casting (HPDC) process. Modeling of dendritic growth of magnesium alloy with six-fold symmetry was achieved by defining a special neighbourhood configuration and calculating of the growth kinetics from complete solution of the transport equations. Special attention was paid to establish a nucleation model considering both of the nucleation of externally solidified crystals in the shot sleeve and the massive nucleation in the die cavity. Meanwhile, simulation of the formation of fully divorced eutectic was also taken into account in the present CA model. Validation was performed and the capability of the present model was addressed by comparing the simulated results with those obtained by experiments.

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Grain size distribution in a complex AM60 magnesium alloy die casting

Cited by 46 publications

References 5 publications

Solute Content and the Grain Microstructure of High Pressure Diecast Magnesium–Aluminium Alloys

Solute Content and the Grain Microstructure of High Pressure Diecast Magnesium–Aluminium Alloys

Grain Size Measurements in Mg-Al High Pressure Die Castings Using Electron Back-Scattered Diffraction (EBSD)

Modeling of microstructure evolution of magnesium alloy during the high pressure die casting process

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