conclusions
The microstructure characterization and mechanical prop- erties were evaluated for four different casting process- es: indirect squeeze cast, Low Pressure Permanent Mold (LPPM), T-Mag, and ablation. Control arms produced by each casting process were provided by different industrial partners. Samples were extracted from the control arms to examine the microstructure, porosity size distribution, and grain size. Four-point bending tests were performed to investigate the mechanical properties and Weibull analy- sis was used to quantify specimens’ failure rates. The fol- lowing conclusions were drawn for the casting processes evaluated:
1. The best two among the four casting processes are T-Mag and ablation according to defect analysis and mechanical testing results.
2. This may be attributed to the quiescent pouring during the T-Mag and ablation processes, which reduces the entrainment of oxide surfaces. The high cooling rate in ablation casting also produces finer grain size and may minimize the unfurling of oxide films.
3. T-Mag castings present better mechanical proper- ties than squeeze cast and LPPM according to the Weibull analysis of FPB test results.
4. Ablation castings present significantly higher duc- tility according to the tensile test results.
5. While the largest average grain size was found in the T-Mag casting, fine dendrites were found in the squeeze casting sample. Both LPPM and ablation castings have similar grain size distribution.
6. Five types of casting defects are identified, in- cluding microporosity, oxide film defects, sponge shrinkage, gas pores, and crack-like defects.
7. Significant shrinkage porosity and oxide film de- fects were observed in the squeeze cast and LPPM specimens.
acknowledgements
This work is part of the USCAR and DOE funded project titled High Integrity Magnesium Automotive Castings (HI- MAC). The authors would like to thank USCAR and DOE for their financial support of this work. The authors also grateful- ly acknowledge valuable discussions with Professor Elborn Jones and the technical assistance of Mr. Jacob Coleman and Mr Wilburn Ray Whittington at Mississippi State University.
Table 4. Summary of Weibull Analysis of UBS for FPB Test Results for each Casting Process
Table 5. Summary of Tensile Results for Each Casting Process
International Journal of Metalcasting/Fall 2011
45
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