High thermal conductivity and high strength magnesium alloy for high pressure die casting ultrathin-walled components

Abstract

With the rapid development of 3C industries, the demand for high-thermal-conductivity magnesium alloys with high mechanical performance is increasing quickly. However, the thermal conductivities of most common Mg foundry alloys (such as Mg—9wt%—1wt%Zn) are still relatively low. In this study, we developed a high-thermal-conductivity Mg—4Al—4Zn—4RE—1Ca (wt%, AZEX4441) alloy with good mechanical properties for ultrathin-walled cellphone components via high-pressure die casting (HPDC). The HPDC AZEX4441 alloy exhibited a fine homogeneous microstructure (average grain size of 2.8 µm) with granular Al₁₁RE₃, fibrous Al₂REZn₂, and networked Ca₆Mg₂Zn₃ phases distributed at the grain boundaries. The room-temperature thermal conductivity of the HPDC AZEX4441 alloy was 94.4 W·m⁻¹·K⁻¹, which was much higher than 53.7 W·m⁻¹K⁻¹ of the HPDC AZ91D alloy. Al and Zn in the AZEX4441 alloy were largely consumed by the formation of Al₁₁RE₃, Al₂REZn₂, and Ca₂Mg₆Zn₃ phases because of the addition of RE and Ca. Therefore, the lattice distortion induced by solute atoms of the AZEX4441 alloy (0.171%) was much lower than that of the AZ91D alloy (0.441%), which was responsible for the high thermal conductivity of the AZEX4441 alloy. The AZEX4441 alloy exhibited a high yield strength of ∼185 MPa, an ultimate tensile strength of ∼233 MPa, and an elongation of ∼4.2%. This result indicated that the tensile properties were comparable with those of the AZ91D alloy. Therefore, this study contributed to the development of high-performance Mg alloys with a combination of high thermal conductivity, high strength, and good castability.

Keywords

magnesium alloys / microstructure / thermal conductivity / mechanical properties / high-pressure die casting

References

[1] Li SB, Yang XY, Hou JT, Du WB. A review on thermal conductivity of magnesium and its alloys. J. Magnesium Alloys, 2020, 8(1): 78.

[2] Rong J, Wang PY, Zha M, Wang C, Xu XY, Wang HY, Jiang QC. Development of a novel strength ductile Mg—7Al—5Zn alloy with high superplasticity processed by hard-plate rolling (HPR). J. Alloys Compd., 2018, 738, 246.

[3] Zhou YY, Fu PH, Peng LM, Wang D, Wang YX, Hu B, Liu M, Sachdev AK, Ding WJ. Precipitation modification in cast Mg—1Nd—1Ce—Zr alloy by Zn addition. J. Magnesium Alloys, 2019, 7(1): 113.

[4] Pan HC, Pan FS, Yang RM, Peng J, Zhao CY, She J, Gao ZY, Tang AT. Thermal and electrical conductivity of binary magnesium alloys. J. Mater. Sci., 2014, 49(8): 3107.

[5] Kulekci MK. Magnesium and its alloys applications in automotive industry. Int. J. Adv. Manuf. Technol., 2008, 39(9–10): 851.

[6] Li XB, Cao WT, Bai YQ. Study on the thermal dispersion of AZ91D. J. Henan Polytech. Univ. Nat. Sci., 2010, 29(5): 685

[7] Hu WX, Yang ZH, Chen GH, Cao YC. Research progress in influence of rare earth on microstructure and mechanical properties of magnesium alloy. Chin. Rare Earths, 2014, 35(5): 89

[8] Li GQ, Zhang JH, Wu RZ, Feng Y, Liu SJ, Wang XJ, Jiao YF, Yang Q, Meng J. Development of high mechanical properties and moderate thermal conductivity cast Mg alloy with multiple RE via heat treatment. J. Mater. Sci. Technol., 2018, 34(7): 1076.

[9] Yuan JW, Zhang K, Zhang XH, Li XG, Li T, Li YJ, Ma ML, Shi GL. Thermal characteristics of Mg—Zn—Mn alloys with high specific strength and high thermal conductivity. J. Alloys Compd., 2013, 578, 32.

[10] Chen CJ, Wang QD, Yin DD. Thermal properties of Mg—11Y—5Gd—2Zn—0.5Zr (wt.%) alloy. J. Alloys Compd., 2009, 487(1–2): 560.

[11] Rudajevová A, Stanĕk M, Lukáč P. Determination of thermal diffusivity and thermal conductivity of Mg-Al alloys. Mater. Sci. Eng. A, 2003, 341(1–2): 152.

[12] Yamasaki M, Kawamura Y. Thermal diffusivity and thermal conductivity of Mg—Zn-rare earth element alloys with long-period stacking ordered phase. Scripta Mater., 2009, 60(4): 264.

[13] Y.F. Liu, X.G. Qiao, Z.T. Li, Z.H. Xia, and M.Y. Zheng, Effect of nano-precipitation on thermal conductivity and mechanical properties of Mg-2Mn-xLa alloys during hot extrusion, J. Alloys Compd., 830(2020), art. No. 154570.

[14] Su CY, Li DJ, Luo AA, Ying T, Zeng XQ. Effect of solute atoms and second phases on the thermal conductivity of Mg—RE alloys: A quantitative study. J. Alloys Compd., 2018, 747, 431.

[15] Xiao WL, Easton MA, Zhu SM, Dargusch MS, Gibson MA, Jia SS, Nie JF. Casting defects and mechanical properties of high pressure die cast Mg—Zn—Al—RE alloys. Adv. Eng. Mater., 2012, 14(1–2): 68.

[16] Hou LF, Wei YH, Li YG, Liu BS, Du HY, Guo CL. Erosion process analysis of die-casting inserts for magnesium alloy components. Eng. Fail. Anal., 2013, 33, 457.

[17] Tian X, Wang LM, Wang JL, Liu YB, An J, Cao ZY. The microstructure and mechanical properties of Mg—3Alv3RE alloys. J. Alloys Compd., 2008, 465(1–2): 412.

[18] Dobrzański LA, Tański T, Čížek L, Brytan Z. Structure and properties of magnesium cast alloys. J. Mater. Process. Technol., 2007, 192–193, 567.

[19] Luo AA. Recent magnesium alloy development for automotive powertrain applications. Mater. Sci. Forum, 2003, 419–422, 57.

[20] Yuan GY, You GQ, Bai SL, Guo W. Effects of heat treatment on the thermal properties of AZ91D magnesium alloys in different casting processes. J. Alloys Compd., 2018, 766, 410.

[21] Anyanwu IA, Gokan Y, Nozawa S, Suzuki A, Kamado S, Kojima Y, Takeda S, Ishida T. Development of new diecastable Mg—Zn—Al—Ca—RE alloys for high temperature applications. Mater. Trans., 2003, 44(4): 562.

[22] Xiao WL, Jia SS, Wang LD, Wu YM, Wang LM. The microstructures and mechanical properties of cast Mg—Zn—Al—RE alloys. J. Alloys Compd., 2009, 480(2): L33.

[23] Shi F, Wang CQ, Guo XF. Microstructures and properties of as-cast Mg₉₂Zn₄Y₄ and Mg₉₂Zn₄Y₃Gd₁ alloys with LPSO phase. Rare Met. Mater. Eng., 2015, 44(7): 1617.

[24] Xiao WL, Easton MA, Dargusch MS, Zhu SM, Gibson MA. The influence of Zn additions on the microstructure and creep resistance of high pressure die cast magnesium alloy AE44. Mater. Sci. Eng. A, 2012, 539, 177.

[25] Belov VD, Koltygin AV, Belov NA, Plisetskaya IV. Innovations in cast magnesium alloys. Metallurgist, 2010, 54(5–6): 317.

[26] Zeng ZR, Zhu YM, Bian MZ, Xu SW, Davies CHJ, Birbilis N, Nie JF. Annealing strengthening in a dilute Mg—Zn—Ca sheet alloy. Scripta Mater., 2015, 107, 127.

[27] Mabuchi M, Higashi K. Strengthening mechanisms of Mg—Si alloys. Acta Mater., 1996, 44(11): 4611.

[28] Homma T, Hirawatari S, Sunohara H, Kamado S. Room and elevated temperature mechanical properties in the as-extruded Mg-Al—Ca—Mn alloys. Mater. Sci. Eng. A, 2012, 539, 163.

[29] Zhu SM, Abbott TB, Gibson MA, Nie JF, Easton MA. Age hardening in die-cast Mg-Al—RE alloys due to minor Mn additions. Mater. Sci. Eng. A, 2016, 656, 34.

[30] Wang F, Xiao WL, Liu MW, Chen J, Li X, Xi JB, Ma CL. Effects of alloying composition on the microstructures and mechanical properties of Mg-Al—Zn—Ca—RE magnesium alloy. Vacuum, 2019, 159, 400.

[31] Xiao WL, Jia SS, Wang J, Wang JL, Wang LM. Investigation on the microstructure and mechanical properties of a cast Mg—6Zn—5Al—4RE alloy. J. Alloys Compd., 2008, 458(1–2): 178.

[32] Zhang WQ, Xiao WL, Wang F, Ma CL. Development of heat resistant Mg—Zn—Al-based magnesium alloys by addition of La and Ca: Microstructure and tensile properties. J. Alloys Compd., 2016, 684, 8.

[33] Dahle AK, Lee YC, Nave MD, Schaffer PL, StJohn DH. Development of the as-cast microstructure in magnesium-aluminium alloys. J. Light. Met., 2001, 1(1): 61.

[34] Tao BR, Qiu RS, Zhao YF, Liu YS, Tan XN, Luan BF, Liu Q. Effects of alloying elements (Sn, Cr and Cu) on second phase particles in Zr—Sn—Nb—Fe—(Cr, Cu) alloys. J. Alloys Compd., 2018, 748, 745.

[35] Wang T. Research on the thermal conductivity of SiC/Al composite. J. Synth. Cryst., 2017, 46(10): 2062

[36] Wang CM, Chen YG, Xiao SF, Ding WC, Liu X. Thermal conductivity and mechanical properties of as-cast Mg—3Zn—(0.5∼3.5)Sn alloys. Rare Met. Mater. Eng., 2013, 42(10): 2019.

[37] Zheng RX, Du JP, Gao S, Somekawa H, Ogata S, Tsuji N. Transition of dominant deformation mode in bulk polycrystalline pure Mg by ultra-grain refinement down to sub-micrometer. Acta Mater., 2020, 198, 35.

[38] Zhang Z, Zhang JH, Wang J, Li ZH, Xie JS, Liu SJ, Guan K, Wu RZ. Toward the development of Mg alloys with simultaneously improved strength and ductility by refining grain size via the deformation process. Int. J. Miner. Metall. Mater., 2021, 28(1): 30.

[39] Ono N, Nowak R, Miura S. Effect of deformation temperature on Hall-Petch relationship registered for polycrystalline magnesium. Mater. Lett., 2004, 58(1–2): 39.

[40] Somekawa H, Mukai T. Hall-Petch relation for deformation twinning in solid solution magnesium alloys. Mater. Sci. Eng. A, 2013, 561, 378.

[41] Wang F, Hu T, Zhang YT, Xiao WL, Ma CL. Effects of Al and Zn contents on the microstructure and mechanical properties of Mg-Al—Zn—Ca magnesium alloys. Mater. Sci. Eng. A, 2017, 704, 57.

[42] Liu SF, Li B, Wang XH, Su W, Han H. Refinement effect of cerium, calcium and strontium in AZ91 magnesium alloy. J. Mater. Process. Technol., 2009, 209(8): 3999.

[43] Kabirian F, Mahmudi R. Effects of rare earth element additions on the impression creep behavior of AZ91 magnesium alloy. Metall. Mater. Trans. A, 2009, 40(9): 2190.

[44] Kondori B, Mahmudi R. Effect of Ca additions on the microstructure, thermal stability and mechanical properties of a cast AM60 magnesium alloy. Mater. Sci. Eng. A, 2010, 527(7–8): 2014.

[45] Luo AA, Sachdev AK. Development of a new wrought magnesium—aluminum—manganese alloy AM30. Metall. Mater. Trans. A, 2007, 38(6): 1184.

[46] Ryen Ø, Holmedal B, Nijs O, Nes E, Sjölander E, Ekström HE. Strengthening mechanisms in solid solution aluminum alloys. Metall. Mater. Trans. A, 2006, 37(6): 1999.