Effects of runner design and pressurization on the microstructure of a high-pressure die cast Mg-3.0Nd-0.3Zn-0.6Zr alloy

Abstract

To clarify the relationship between externally solidified crystals (ESCs) and other defects, e.g., defect bands and pores, two dimensional (2D) and three dimensional (3D) characterization methods were adopted to analyze castings produced using a modified ingate system equipped with and without an ESC collector. The reduction of ESCs strongly reduced defect band width and shrinkage pore quantity. By reducing the quantity and size of ESCs, net-shrinkage pores were transformed into isolated island-shrinkage pores. We determined via statistical analysis that the mechanical properties of high pressure die castings were strongly related to the size and fraction of the ESCs rather than porosity volume. The reduction of ESCs also caused tensile transgranular fracture modes to transform into intergranular fracture modes. Additionally, casting pressurization strongly reduced pore morphology, volume, and size.

Keywords

high-pressure die casting / externally solidified crystals / porosity / 3D reconstruction / runner design

References

[1] Rong J, Xiao WL, Zhao XQ, Ma CL, Liao HM, He DL, Chen M, Huang M, Huang C. High thermal conductivity and high strength magnesium alloy for high pressure die cast ultrathin-walled component. Int. J. Miner. Metall. Mater., 2022, 29(1): 88.

[2] Wu GH, Wang CL, Sun M, Ding WJ. Recent developments and applications on high-performance cast magnesium rare-earth alloys. J. Magnes. Alloys, 2021, 9(1): 1.

[3] Wang KK, Kang YL, Zhang K. Effects of rare earth elements on the microstructure and properties of magnesium alloy AZ91D. J. Univ. Sci. Technol. Beijing, 2002, 9(5): 363

[4] Laukli HI, Arnberg L, Lohne O. Effects of grain refiner additions on the grain structures in HPDC A356 castings. Int. J. Cast Met. Res., 2005, 18(2): 65.

[5] Sheggaf ZM, Ahmad R, Asmael MBA, Elaswad AMM. Solidification, microstructure, and mechanical properties of the as-cast ZRE1 magnesium alloy with different praseodymium contents. Int. J. Miner. Metall. Mater., 2017, 24(11): 1306.

[6] Weiler JP, Wood JT, Klassen RJ, Maire E, Berkmortel R, Wang G. Relationship between internal porosity and fracture strength of die-cast magnesium AM60B alloy. Mater. Sci. Eng. A, 2005, 395(1–2): 315.

[7] Lee SG, Patel GR, Gokhale AM. A. Sreeranganathan, and M.F. Horstemeyer, Variability in the tensile ductility of high-pressure die-cast AM50 Mg-alloy. Scripta Mater, 2005, 53(7): 851.

[8] Lee SG, Patel GR, Gokhale AM, Sreeranganathan A, Horstemeyer MF. Quantitative fractographic analysis of variability in the tensile ductility of high-pressure die-cast AE44 Mg-alloy. Mater. Sci. Eng. A, 2006, 427(1–2): 255.

[9] Yu WB, Cao YY, Li XB, Guo ZP, Xiong SM. Determination of interfacial heat transfer behavior at the metal/shot sleeve of high pressure die casting process of AZ91D alloy. J. Mater. Sci. Technol., 2017, 33(1): 52.

[10] Helenius R, Lohne O, Arnberg L, Laukli HI. The heat transfer during filling of a high-pressure die-casting shot sleeve. Mater. Sci. Eng. A, 2005, 413–414, 52.

[11] Yu WB, Cao YY, Guo ZP, Xiong SM. Development and application of inverse heat transfer model between liquid metal and shot sleeve in high pressure die casting process under non-shooting condition. China Foundry, 2016, 13(4): 269.

[12] Barbagallo S. Shrinkage porosity in thin walled AM60 HPDC magnesium alloy U-shaped box. Int. J. Cast Met. Res., 2004, 17(6): 364.

[13] Li XB, Guo ZP, Xiong SM. Influence of melt flow on the formation of defect band in high pressure die casting of AZ91D magnesium alloy. Mater. Charact., 2017, 129, 344.

[14] W.B. Yu, C.S. Ma, Y.H. Ma, and S.M. Xiong, Correlation of 3D defect-band morphologies and mechanical properties in high pressure die casting magnesium alloy, J. Mater. Process. Technol., 288(2021), art. No. 116853.

[15] Li X, Xiong SM, Guo Z. On the tensile failure induced by defect band in high pressure die casting of AM60B magnesium alloy. Mater. Sci. Eng. A, 2016, 674, 687.

[16] Li X, Xiong SM, Guo Z. Failure behavior of high pressure die casting AZ91D magnesium alloy. Mater. Sci. Eng. A, 2016, 672, 216.

[17] Wang QL, Xiong SM. Effect of multi-step slow shot speed on microstructure of vacuum die cast AZ91D magnesium alloy. Trans. Nonferrous Met. Soc. China, 2015, 25(2): 375.

[18] Lee SG, Gokhale AM. Formation of gas induced shrinkage porosity in Mg-alloy high-pressure die-castings. Scripa Mater., 2006, 55(4): 387.

[19] Lee BD, Baek UH, Han JW. Optimization of gating system design for die casting of thin magnesium alloy-based multi-cavity LCD housings. J. Mater. Eng. Perform., 2012, 21(9): 1893.

[20] Gunasegaram DR, Givord M, O’Donnell RG, Finnin BR. Improvements engineered in UTS and elongation of aluminum alloy high pressure die castings through the alteration of runner geometry and plunger velocity. Mater. Sci. Eng. A, 2013, 559, 276.

[21] Zhou Y, Guo Z, Xiong SM. Effect of runner design on the externally solidified crystals in vacuum die-cast Mg-3.0Nd-0.3Zn-0.6Zr alloy. J. Mater. Process. Technol., 2019, 267, 366.

[22] Li X, Xiong SM, Guo Z. Improved mechanical properties in vacuum-assist high-pressure die casting of AZ91D alloy. J. Mater. Process. Technol., 2016, 231, 1.

[23] Z.X. Li, D.J. Li, W.K. Zhou, B. Hu, X.F. Zhao, J.Y. Wang, M. Qin, J.K. Xu, and X.Q. Zeng, Characterization on the formation of porosity and tensile properties prediction in die casting Mg alloys, J. Magnes. Alloys, (2021). DOI: https://doi.org/10.1016/j.jma.2020.12.006

[24] C.S. Ma, W.B. Yu, T.T. Zhang, Z.H. Zhang, Y.H. Ma, and S.M. Xiong, The effect of slow shot speed and casting pressure on the 3D microstructure of high pressure die casting AE44 magnesium alloy, J. Magnes. Alloys, (2021). DOI: https://doi.org/10.1016/j.jma.2021.09.011

[25] Guo ZP, Xiong SM, Li M, Allison J. Relationship between metal-die interfacial heat transfer coefficient and casting solidification rate in high pressure die casting process. Acta Metall. Sin., 2009, 45(1): 102

[26] Song J, Xiong SM, Li M, Allison J. The correlation between microstructure and mechanical properties of high-pressure die-cast AM50 alloy. J. Alloys Compd., 2009, 477(1–2): 863.

[27] Sun X, Choi KS, Li DS. Predicting the influence of pore characteristics on ductility of thin-walled high pressure die casting magnesium. Mater. Sci. Eng. A, 2013, 572, 45.