Variability of skin thickness in an AM60B magnesium alloy die-casting

Weiler, J.P.; Wood, Jeffrey; Klassen, Robert D.; Berkmortel, R.; Wang, G.

doi:10.1016/j.msea.2006.01.034

Cited by 55 publications

(26 citation statements)

References 7 publications

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“…It is noted in passing that the average grain sizes in Figure 4 are consistent with those reported by Bowles et al [30] and Weiler et al [32] for alloys AM60 and AZ91.…”

Section: Resultssupporting

confidence: 89%

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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“…It is noted in passing that the average grain sizes in Figure 4 are consistent with those reported by Bowles et al [30] and Weiler et al [32] for alloys AM60 and AZ91.…”

Section: Resultssupporting

confidence: 89%

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

2009

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“…[7,26,27] Although it currently has no universal definition, [8,17] the skin is usually free of porosity and harder than more central regions, and can be up to several hundred micrometers thick. [7,17,24,25] Some authors have defined the skin as the region outside the defect band.…”

Section: Defect Bands and The Hpdc Skinmentioning

confidence: 99%

Defect Band Characteristics in Mg-Al and Al-Si High-Pressure Die Castings

Gourlay

Laukli

Dahle

2007

Metall Mater Trans A

118

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Bands of positive macrosegregation and porosity commonly follow the surface contour of components produced by high-pressure die casting (HPDC). In this article, Al alloy AlSi7Mg and Mg alloys AZ91 and AM60 were cast into tensile test bars using cold-chamber (cc) HPDC. Microstructural characterization revealed that externally solidified crystals (ESCs) are not necessary for defect band formation, and that defect bands can form both near to and relatively far from any surface layer of different microstructure. The defect bands were 140 to 240 lm thick. In addition to defect-band-related macrosegregation, the castings also contained inverse segregation and surface segregation. Defect bands are shown to have the characteristics of the dilatant shear bands reported in past rheology studies, indicating that defect bands form due to strain localization in partially solid material during the HPDC process.

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“…Alain et al [58] proposed that the variability observed in tensile tests was due to the removal of the as-cast surface during machining of the sample and much of the resulting scatter in the results was due to the exposure of internal porosity or other defects due to the machining. Weiler et al [13,14] and Yang et al [59][60][61] have reported the pronounced decreases in mechanical properties in Mg alloys between areas closest to the surface ('skin') and areas in the middle of the cross section ('core'). Therefore, the act of excising and testing a tensile sample from a component could indicate more mechanical property variation, particularly in elongation at failure, than actually exists in the cast component.…”

Section: Discussionmentioning

confidence: 99%

“…The upper window was machined away prior to testing. based on the authors' previous experience and some earlier work from other researchers [4,6,13,14]. Flow length is the length a virtual marker travels in the die cavity before it solidifies.…”

Section: Derivation Of the Quality Mapping Equationsmentioning

confidence: 99%

Using quality mapping to predict spatial variation in local properties and component performance in Mg alloy thin-walled high-pressure die castings: an ICME approach and case study

Forsmark

Zindel

Godlewski

et al. 2015

Integr Mater Manuf Innov

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This paper explores the use of quality mapping for the prediction of the spatial variation in local properties in thin-walled high-pressure die castings (HPDC) of the magnesium alloy AM60. The work investigates the role of casting parameters on local ductility and yield strength and presents a model for predicting local ductility and yield strength in a cast component. A design of experiment (DOE) was created to examine the role of various casting parameters on local properties such as ductility and yield strength. Over 1,200 tensile samples were excised from cast parts and tested. Casting simulations were also conducted for each experimental condition. Local properties were predicted, and the local property (quality map) model was compared with a prototype production component. The results of this model were used as input to a performance simulation software code to simulate the component-level behavior under two different loading conditions. In this study, the authors bypassed the traditional Integrated Computational Materials Engineering (ICME; process-microstructure-properties) approach in favor of a semi-empirical quality mapping approach to provide estimates of manufacturing sensitive local properties for use in process and component design.

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Variability of skin thickness in an AM60B magnesium alloy die-casting

Cited by 55 publications

References 7 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

Defect Band Characteristics in Mg-Al and Al-Si High-Pressure Die Castings

Using quality mapping to predict spatial variation in local properties and component performance in Mg alloy thin-walled high-pressure die castings: an ICME approach and case study

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