ATEM’11, JSME-MMD, September 19-21, 2011, Kobe, Japan

Multiscale Modeling and Analysis of Die Cast Aluminum Alloy toConsider Clustered Shrinkage PoresOsamu Kuwazuru1*, Takayuki Yano2, Yoshihiko Hangai2, Takao Utsunomiya3,Sujit Bidhar4, Yoshinori Shiihara4, Soichiro Kitahara5 and Nobuhiro Yoshikawa4
1

Department of Nuclear Power & Energy Safety, University of Fukui, 3-9-1 Bunkyo, Fukui 910-8507, Japan2
Department of Mechanical System Engineering, Gunma University, Gunma, Japan
3
Research Organization of Advanced Engineering, Shibaura Institute of Technology, Saitama, Japan4
Institute of Industrial Science, The University of Tokyo, Tokyo, Japan
5Gundai Co., Ltd., Gunma, Japan*kuwa@u-fukui.ac.jp

Keywords: Aluminum Alloy, Casting Defect, Fatigue, Image-Based Modeling, Homogenization Method
A multiscale stress analysis method is demonstrated to evaluate the strength of die cast aluminum alloy including theclustered shrinkage pores (CSP), which is sometimes generated around large gas pores(1). The CSP has extremelycomplicated shape of cavity, which leads to locally high elastic compliance and high stress concentration(2). Hence, it
considerably reduces the fatigue strength and structural reliability. To evaluate the effect of porosities on the fatigue
strength of die cast aluminum alloys, we carried out the image-based finite element analysis(3). The X-ray CT wasemployed to construct a geometrical model of actual macroscopic pores. Due to the lack of resolution of the X-ray CT
used in this study, the microscopic pores such as CSP could not be visualized. However, the region of CSP can berecognized as an ambiguous grey area in the CT image, because of high X-ray transmittance by the porous geometry.
To compensate for the lack of resolution of CT image, we carried out successive polishing and digital optical
microscopy of CSP specimen, and constructed microscopic model of CSP based on the serial sectioning images.
Moreover, we utilized the homogenization method with the microscopic model and obtained the relationship between
porosity and equivalent elastic constants, which were used for the macroscopic property of CSP region. Thus, wecarried out the multiscale analysis by using the two-scale images of CT and micrograph. The macroscopic model was
separated to bulk region and CSP regions depending on the pixel intensity in X-ray CT images. The microscopic model
based on the serial sectioning images was embedded in the CSP region, and its equivalent elastic constants were used as
the macroscopic material property of CSP region.
The multiscale analysis was carried out for the fatigue specimen(3) of ADC12 high-pressure die cast aluminum alloy,
whose fatigue life was 14694 cycles under the stress amplitude of 90 MPa and stress ratio of 1. Young’s modulus andPoisson’s ratio of ADC12 were set to 74.5GPa and 0.3, respectively. The static extension corresponding to the stressamplitude was analyzed. Large gas pores and CSP, as shown in Fig. 1, were included in the fatigue specimen. The CSP
was expanding among the gas pores. Figure 2 shows the microscopic model of porosity volume fraction of 11.4%
obtained elsewhere and used in the multiscale analysis. The obtained distribution of maximum principal stress inlongitudinal section was shown in Fig. 3, and compared to the fracture surface. The good agreement between the pointof maximum stress and the fracture surface was confirmed as a validity of the present simulation.

Fig. 1 Geometry of CSP

Fig. 2 Micro model of CSP

Fig. 3 Stress and fracture surface(1) Kuwazuru, O., et al., X-Ray CT Inspection for Porosities and Its Effect on Fatigue of Die Cast Aluminum Alloy,
Journal of Solid Mechanics and Materials Engineering, Vol. 2 (2008), pp. 1220-1231.
(2) Hangai, Y., et al., Clustered Shrinkage Pores in Ill-Conditioned Aluminum Alloy Die Castings, Materials
Transactions, Vol. 51, No. 9 (2010), pp. 1574-1580.
(3) Kuwazuru, O., et al., Quantitative Evaluation of Porosity Effect on Fatigue Strength of High Pressure Die Cast
Aluminum Alloy (Part 2, Fatigue Strength Prediction Based on Elastic Stress Field around Pores), Transactions ofthe Japan Society of Mechanical Engineers, Series A, Vol. 77, No. 773 (2011), pp. 48-57.